File: managed_memory_segments.html

package info (click to toggle)
boost1.55 1.55.0%2Bdfsg-3
  • links: PTS, VCS
  • area: main
  • in suites: jessie, jessie-kfreebsd
  • size: 487,824 kB
  • ctags: 673,349
  • sloc: cpp: 2,098,430; xml: 106,036; ansic: 46,744; python: 32,427; sh: 11,864; cs: 2,121; asm: 1,640; makefile: 984; perl: 714; yacc: 456; php: 132; fortran: 43; sql: 13; csh: 6
file content (2491 lines) | stat: -rw-r--r-- 256,295 bytes parent folder | download 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
 
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Managed Memory Segments</title>
<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset">
<link rel="up" href="../interprocess.html" title="Chapter&#160;14.&#160;Boost.Interprocess">
<link rel="prev" href="synchronization_mechanisms.html" title="Synchronization mechanisms">
<link rel="next" href="allocators_containers.html" title="Allocators, containers and memory allocation algorithms">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td>
<td align="center"><a href="../../../index.html">Home</a></td>
<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="synchronization_mechanisms.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../interprocess.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="allocators_containers.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="interprocess.managed_memory_segments"></a><a class="link" href="managed_memory_segments.html" title="Managed Memory Segments">Managed Memory Segments</a>
</h2></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.making_ipc_easy">Making
      Interprocess Data Communication Easy</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory">Managed
      Shared Memory</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_mapped_files">Managed
      Mapped File</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features">Managed
      Memory Segment Features</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features">Managed
      Memory Segment Advanced Features</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer">Managed
      Heap Memory And Managed External Buffer</a></span></dt>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="interprocess.managed_memory_segments.making_ipc_easy"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.making_ipc_easy" title="Making Interprocess Data Communication Easy">Making
      Interprocess Data Communication Easy</a>
</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.making_ipc_easy.managed_memory_segments_intro">Introduction</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.making_ipc_easy.managed_memory_segment_int">Declaration
        of managed memory segment classes</a></span></dt>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.making_ipc_easy.managed_memory_segments_intro"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.making_ipc_easy.managed_memory_segments_intro" title="Introduction">Introduction</a>
</h4></div></div></div>
<p>
          As we have seen, <span class="bold"><strong>Boost.Interprocess</strong></span> offers
          some basic classes to create shared memory objects and file mappings and
          map those mappable classes to the process' address space.
        </p>
<p>
          However, managing those memory segments is not not easy for non-trivial
          tasks. A mapped region is a fixed-length memory buffer and creating and
          destroying objects of any type dynamically, requires a lot of work, since
          it would require programming a memory management algorithm to allocate
          portions of that segment. Many times, we also want to associate names to
          objects created in shared memory, so all the processes can find the object
          using the name.
        </p>
<p>
          <span class="bold"><strong>Boost.Interprocess</strong></span> offers 4 managed memory
          segment classes:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              To manage a shared memory mapped region (<span class="bold"><strong>basic_managed_shared_memory</strong></span>
              class).
            </li>
<li class="listitem">
              To manage a memory mapped file (<span class="bold"><strong>basic_managed_mapped_file</strong></span>).
            </li>
<li class="listitem">
              To manage a heap allocated (<code class="computeroutput"><span class="keyword">operator</span>
              <span class="keyword">new</span></code>) memory buffer (<span class="bold"><strong>basic_managed_heap_memory</strong></span> class).
            </li>
<li class="listitem">
              To manage a user provided fixed size buffer (<span class="bold"><strong>basic_managed_external_buffer</strong></span>
              class).
            </li>
</ul></div>
<p>
          The first two classes manage memory segments that can be shared between
          processes. The third is useful to create complex data-bases to be sent
          though other mechanisms like message queues to other processes. The fourth
          class can manage any fixed size memory buffer. The first two classes will
          be explained in the next two sections. <span class="bold"><strong>basic_managed_heap_memory</strong></span>
          and <span class="bold"><strong>basic_managed_external_buffer</strong></span> will
          be explained later.
        </p>
<p>
          The most important services of a managed memory segment are:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              Dynamic allocation of portions of a memory the segment.
            </li>
<li class="listitem">
              Construction of C++ objects in the memory segment. These objects can
              be anonymous or we can associate a name to them.
            </li>
<li class="listitem">
              Searching capabilities for named objects.
            </li>
<li class="listitem">
              Customization of many features: memory allocation algorithm, index
              types or character types.
            </li>
<li class="listitem">
              Atomic constructions and destructions so that if the segment is shared
              between two processes it's impossible to create two objects associated
              with the same name, simplifying synchronization.
            </li>
</ul></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.making_ipc_easy.managed_memory_segment_int"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.making_ipc_easy.managed_memory_segment_int" title="Declaration of managed memory segment classes">Declaration
        of managed memory segment classes</a>
</h4></div></div></div>
<p>
          All <span class="bold"><strong>Boost.Interprocess</strong></span> managed memory
          segment classes are templatized classes that can be customized by the user:
        </p>
<pre class="programlisting"><span class="keyword">template</span>
      <span class="special">&lt;</span>
         <span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span>
         <span class="keyword">class</span> <span class="identifier">MemoryAlgorithm</span><span class="special">,</span>
         <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">IndexConfig</span><span class="special">&gt;</span> <span class="keyword">class</span> <span class="identifier">IndexType</span>
      <span class="special">&gt;</span>
<span class="keyword">class</span> <span class="identifier">basic_managed_shared_memory</span> <span class="special">/</span> <span class="identifier">basic_managed_mapped_file</span> <span class="special">/</span>
      <span class="identifier">basic_managed_heap_memory</span>   <span class="special">/</span> <span class="identifier">basic_external_buffer</span><span class="special">;</span>
</pre>
<p>
          These classes can be customized with the following template parameters:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              <span class="bold"><strong>CharType</strong></span> is the type of the character
              that will be used to identify the created named objects (for example,
              <span class="bold"><strong>char</strong></span> or <span class="bold"><strong>wchar_t</strong></span>)
            </li>
<li class="listitem">
              <span class="bold"><strong>MemoryAlgorithm</strong></span> is the memory algorithm
              used to allocate portions of the segment (for example, rbtree_best_fit
              ). The internal typedefs of the memory algorithm also define:
              <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                    The synchronization type (<code class="computeroutput"><span class="identifier">MemoryAlgorithm</span><span class="special">::</span><span class="identifier">mutex_family</span></code>)
                    to be used in all allocation operations. This allows the use
                    of user-defined mutexes or avoiding internal locking (maybe code
                    will be externally synchronized by the user).
                  </li>
<li class="listitem">
                    The Pointer type (<code class="computeroutput"><span class="identifier">MemoryAlgorithm</span><span class="special">::</span><span class="identifier">void_pointer</span></code>)
                    to be used by the memory allocation algorithm or additional helper
                    structures (like a map to maintain object/name associations).
                    All STL compatible allocators and containers to be used with
                    this managed memory segment will use this pointer type. The pointer
                    type will define if the managed memory segment can be mapped
                    between several processes. For example, if <code class="computeroutput"><span class="identifier">void_pointer</span></code>
                    is <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span></code> we will be able to map the
                    managed segment in different base addresses in each process.
                    If <code class="computeroutput"><span class="identifier">void_pointer</span></code>
                    is <code class="computeroutput"><span class="keyword">void</span><span class="special">*</span></code>
                    only fixed address mapping could be used.
                  </li>
<li class="listitem">
                    See <a class="link" href="customizing_interprocess.html#interprocess.customizing_interprocess.custom_interprocess_alloc" title="Writing a new shared memory allocation algorithm">Writing
                    a new memory allocation algorithm</a> for more details about
                    memory algorithms.
                  </li>
</ul></div>
            </li>
<li class="listitem">
              <span class="bold"><strong>IndexType</strong></span> is the type of index that
              will be used to store the name-object association (for example, a map,
              a hash-map, or an ordered vector).
            </li>
</ul></div>
<p>
          This way, we can use <code class="computeroutput"><span class="keyword">char</span></code>
          or <code class="computeroutput"><span class="keyword">wchar_t</span></code> strings to identify
          created C++ objects in the memory segment, we can plug new shared memory
          allocation algorithms, and use the index type that is best suited to our
          needs.
        </p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="interprocess.managed_memory_segments.managed_shared_memory"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory" title="Managed Shared Memory">Managed
      Shared Memory</a>
</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.managed_memory_common_shm">Common
        Managed Shared Memory Classes</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.constructing_managed_shared_memories">Constructing
        Managed Shared Memory</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.windows_managed_memory_common_shm">Using
        native windows shared memory</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.xsi_managed_memory_common_shm">Using
        XSI (system V) shared memory</a></span></dt>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_shared_memory.managed_memory_common_shm"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.managed_memory_common_shm" title="Common Managed Shared Memory Classes">Common
        Managed Shared Memory Classes</a>
</h4></div></div></div>
<p>
          As seen, <span class="bold"><strong>basic_managed_shared_memory</strong></span> offers
          a great variety of customization. But for the average user, a common, default
          shared memory named object creation is needed. Because of this, <span class="bold"><strong>Boost.Interprocess</strong></span> defines the most common managed
          shared memory specializations:
        </p>
<pre class="programlisting"><span class="comment">//!Defines a managed shared memory with c-strings as keys for named objects,</span>
<span class="comment">//!the default memory algorithm (with process-shared mutexes,</span>
<span class="comment">//!and offset_ptr as internal pointers) as memory allocation algorithm</span>
<span class="comment">//!and the default index type as the index.</span>
<span class="comment">//!This class allows the shared memory to be mapped in different base</span>
<span class="comment">//!in different processes</span>
<span class="keyword">typedef</span>
   <span class="identifier">basic_managed_shared_memory</span><span class="special">&lt;</span><span class="keyword">char</span>
                              <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">memory</span> <span class="identifier">algorithm</span> <span class="identifier">defining</span> <span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">as</span> <span class="identifier">void_pointer</span><span class="special">*/</span>
                              <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">index</span> <span class="identifier">type</span><span class="special">*/&gt;</span>
   <span class="identifier">managed_shared_memory</span><span class="special">;</span>

<span class="comment">//!Defines a managed shared memory with wide strings as keys for named objects,</span>
<span class="comment">//!the default memory algorithm (with process-shared mutexes,</span>
<span class="comment">//!and offset_ptr as internal pointers) as memory allocation algorithm</span>
<span class="comment">//!and the default index type as the index.</span>
<span class="comment">//!This class allows the shared memory to be mapped in different base</span>
<span class="comment">//!in different processes</span>
<span class="keyword">typedef</span>
   <span class="identifier">basic_managed_shared_memory</span><span class="special">&lt;</span><span class="keyword">wchar_t</span>
                              <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">memory</span> <span class="identifier">algorithm</span> <span class="identifier">defining</span> <span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">as</span> <span class="identifier">void_pointer</span><span class="special">*/</span>
                              <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">index</span> <span class="identifier">type</span><span class="special">*/&gt;</span>
   <span class="identifier">wmanaged_shared_memory</span><span class="special">;</span>
</pre>
<p>
          <code class="computeroutput"><span class="identifier">managed_shared_memory</span></code> allocates
          objects in shared memory associated with a c-string and <code class="computeroutput"><span class="identifier">wmanaged_shared_memory</span></code>
          allocates objects in shared memory associated with a wchar_t null terminated
          string. Both define the pointer type as <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span></code> so they can be used to map the shared
          memory at different base addresses in different processes.
        </p>
<p>
          If the user wants to map the shared memory in the same address in all processes
          and want to use raw pointers internally instead of offset pointers, <span class="bold"><strong>Boost.Interprocess</strong></span> defines the following types:
        </p>
<pre class="programlisting"><span class="comment">//!Defines a managed shared memory with c-strings as keys for named objects,</span>
<span class="comment">//!the default memory algorithm (with process-shared mutexes,</span>
<span class="comment">//!and offset_ptr as internal pointers) as memory allocation algorithm</span>
<span class="comment">//!and the default index type as the index.</span>
<span class="comment">//!This class allows the shared memory to be mapped in different base</span>
<span class="comment">//!in different processes*/</span>
<span class="keyword">typedef</span> <span class="identifier">basic_managed_shared_memory</span>
   <span class="special">&lt;</span><span class="keyword">char</span>
   <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">memory</span> <span class="identifier">algorithm</span> <span class="identifier">defining</span> <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">as</span> <span class="identifier">void_pointer</span><span class="special">*/</span>
   <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">index</span> <span class="identifier">type</span><span class="special">*/&gt;</span>
<span class="identifier">fixed_managed_shared_memory</span><span class="special">;</span>

<span class="comment">//!Defines a managed shared memory with wide strings as keys for named objects,</span>
<span class="comment">//!the default memory algorithm (with process-shared mutexes,</span>
<span class="comment">//!and offset_ptr as internal pointers) as memory allocation algorithm</span>
<span class="comment">//!and the default index type as the index.</span>
<span class="comment">//!This class allows the shared memory to be mapped in different base</span>
<span class="comment">//!in different processes</span>
<span class="keyword">typedef</span> <span class="identifier">basic_managed_shared_memory</span>
   <span class="special">&lt;</span><span class="keyword">wchar_t</span>
   <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">memory</span> <span class="identifier">algorithm</span> <span class="identifier">defining</span> <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">as</span> <span class="identifier">void_pointer</span><span class="special">*/</span>
   <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">index</span> <span class="identifier">type</span><span class="special">*/&gt;</span>
<span class="identifier">wfixed_managed_shared_memory</span><span class="special">;</span>
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_shared_memory.constructing_managed_shared_memories"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.constructing_managed_shared_memories" title="Constructing Managed Shared Memory">Constructing
        Managed Shared Memory</a>
</h4></div></div></div>
<p>
          Managed shared memory is an advanced class that combines a shared memory
          object and a mapped region that covers all the shared memory object. That
          means that when we <span class="bold"><strong>create</strong></span> a new managed
          shared memory:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              A new shared memory object is created.
            </li>
<li class="listitem">
              The whole shared memory object is mapped in the process' address space.
            </li>
<li class="listitem">
              Some helper objects are constructed (name-object index, internal synchronization
              objects, internal variables...) in the mapped region to implement managed
              memory segment features.
            </li>
</ul></div>
<p>
          When we <span class="bold"><strong>open</strong></span> a managed shared memory
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              A shared memory object is opened.
            </li>
<li class="listitem">
              The whole shared memory object is mapped in the process' address space.
            </li>
</ul></div>
<p>
          To use a managed shared memory, you must include the following header:
        </p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<pre class="programlisting"><span class="comment">//1.  Creates a new shared memory object</span>
<span class="comment">//    called "MySharedMemory".</span>
<span class="comment">//2.  Maps the whole object to this</span>
<span class="comment">//    process' address space.</span>
<span class="comment">//3.  Constructs some objects in shared memory</span>
<span class="comment">//    to implement managed features.</span>
<span class="comment">//!!  If anything fails, throws interprocess_exception</span>
<span class="comment">//</span>
<span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span>      <span class="special">(</span> <span class="identifier">create_only</span>
                                   <span class="special">,</span> <span class="string">"MySharedMemory"</span> <span class="comment">//Shared memory object name</span>
                                   <span class="special">,</span> <span class="number">65536</span><span class="special">);</span>          <span class="comment">//Shared memory object size in bytes</span>
</pre>
<pre class="programlisting"><span class="comment">//1.  Opens a shared memory object</span>
<span class="comment">//    called "MySharedMemory".</span>
<span class="comment">//2.  Maps the whole object to this</span>
<span class="comment">//    process' address space.</span>
<span class="comment">//3.  Obtains pointers to constructed internal objects</span>
<span class="comment">//    to implement managed features.</span>
<span class="comment">//!!  If anything fails, throws interprocess_exception</span>
<span class="comment">//</span>
<span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span>      <span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span>       <span class="string">"MySharedMemory"</span><span class="special">);//</span><span class="identifier">Shared</span> <span class="identifier">memory</span> <span class="identifier">object</span> <span class="identifier">name</span>
</pre>
<pre class="programlisting"><span class="comment">//1.  If the segment was previously created</span>
<span class="comment">//    equivalent to "open_only" (size is ignored).</span>
<span class="comment">//2.  Otherwise, equivalent to "create_only"</span>
<span class="comment">//!!  If anything fails, throws interprocess_exception</span>
<span class="comment">//</span>
<span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span>      <span class="special">(</span> <span class="identifier">open_or_create</span>
                                   <span class="special">,</span> <span class="string">"MySharedMemory"</span> <span class="comment">//Shared memory object name</span>
                                   <span class="special">,</span> <span class="number">65536</span><span class="special">);</span>          <span class="comment">//Shared memory object size in bytes</span>
</pre>
<p>
          When the <code class="computeroutput"><span class="identifier">managed_shared_memory</span></code>
          object is destroyed, the shared memory object is automatically unmapped,
          and all the resources are freed. To remove the shared memory object from
          the system you must use the <code class="computeroutput"><span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span></code>
          function. Shared memory object removing might fail if any process still
          has the shared memory object mapped.
        </p>
<p>
          The user can also map the managed shared memory in a fixed address. This
          option is essential when using using <code class="computeroutput"><span class="identifier">fixed_managed_shared_memory</span></code>.
          To do this, just add the mapping address as an extra parameter:
        </p>
<pre class="programlisting"><span class="identifier">fixed_managed_shared_memory</span> <span class="identifier">segment</span>      <span class="special">(</span><span class="identifier">open_only</span>      <span class="special">,</span><span class="string">"MyFixedAddressSharedMemory"</span> <span class="comment">//Shared memory object name</span>
   <span class="special">,(</span><span class="keyword">void</span><span class="special">*)</span><span class="number">0x30000000</span>            <span class="comment">//Mapping address</span>
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_shared_memory.windows_managed_memory_common_shm"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.windows_managed_memory_common_shm" title="Using native windows shared memory">Using
        native windows shared memory</a>
</h4></div></div></div>
<p>
          Windows users might also want to use native windows shared memory instead
          of the portable <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_memory_object.html" title="Class shared_memory_object">shared_memory_object</a></code>
          managed memory. This is achieved through the <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_managed__idp27948200.html" title="Class template basic_managed_windows_shared_memory">basic_managed_windows_shared_memory</a></code>
          class. To use it just include:
        </p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_windows_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
          This class has the same interface as <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_managed__idp27927368.html" title="Class template basic_managed_shared_memory">basic_managed_shared_memory</a></code>
          but uses native windows shared memory. Note that this managed class has
          the same lifetime issues as the windows shared memory: when the last process
          attached to the windows shared memory is detached from the memory (or ends/crashes)
          the memory is destroyed. So there is no persistence support for windows
          shared memory.
        </p>
<p>
          To communicate between system services and user applications using <code class="computeroutput"><span class="identifier">managed_windows_shared_memory</span></code>, please
          read the explanations given in chapter <a class="link" href="sharedmemorybetweenprocesses.html#interprocess.sharedmemorybetweenprocesses.sharedmemory.windows_shared_memory" title="Native windows shared memory">Native
          windows shared memory</a>.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_shared_memory.xsi_managed_memory_common_shm"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.xsi_managed_memory_common_shm" title="Using XSI (system V) shared memory">Using
        XSI (system V) shared memory</a>
</h4></div></div></div>
<p>
          Unix users might also want to use XSI (system V) instead of the portable
          <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_memory_object.html" title="Class shared_memory_object">shared_memory_object</a></code>
          managed memory. This is achieved through the <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_managed__idp27967224.html" title="Class template basic_managed_xsi_shared_memory">basic_managed_xsi_shared_memory</a></code>
          class. To use it just include:
        </p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_xsi_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
          This class has nearly the same interface as <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_managed__idp27927368.html" title="Class template basic_managed_shared_memory">basic_managed_shared_memory</a></code>
          but uses XSI shared memory as backend.
        </p>
</div>
<p>
        For more information about managed XSI shared memory capabilities, see <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_managed__idp27967224.html" title="Class template basic_managed_xsi_shared_memory">basic_managed_xsi_shared_memory</a></code>
        class reference.
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="interprocess.managed_memory_segments.managed_mapped_files"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_mapped_files" title="Managed Mapped File">Managed
      Mapped File</a>
</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_mapped_files.managed_memory_common_mfile">Common
        Managed Mapped Files</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_mapped_files.constructing_managed_mapped_files">Constructing
        Managed Mapped Files</a></span></dt>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_mapped_files.managed_memory_common_mfile"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_mapped_files.managed_memory_common_mfile" title="Common Managed Mapped Files">Common
        Managed Mapped Files</a>
</h4></div></div></div>
<p>
          As seen, <span class="bold"><strong>basic_managed_mapped_file</strong></span> offers
          a great variety of customization. But for the average user, a common, default
          shared memory named object creation is needed. Because of this, <span class="bold"><strong>Boost.Interprocess</strong></span> defines the most common managed
          mapped file specializations:
        </p>
<pre class="programlisting"><span class="comment">//Named object creation managed memory segment</span>
<span class="comment">//All objects are constructed in the memory-mapped file</span>
<span class="comment">//   Names are c-strings,</span>
<span class="comment">//   Default memory management algorithm(rbtree_best_fit with no mutexes)</span>
<span class="comment">//   Name-object mappings are stored in the default index type (flat_map)</span>
<span class="keyword">typedef</span> <span class="identifier">basic_managed_mapped_file</span> <span class="special">&lt;</span>
   <span class="keyword">char</span><span class="special">,</span>
   <span class="identifier">rbtree_best_fit</span><span class="special">&lt;</span><span class="identifier">mutex_family</span><span class="special">,</span> <span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="special">&gt;,</span>
   <span class="identifier">flat_map_index</span>
   <span class="special">&gt;</span>  <span class="identifier">managed_mapped_file</span><span class="special">;</span>

<span class="comment">//Named object creation managed memory segment</span>
<span class="comment">//All objects are constructed in the memory-mapped file</span>
<span class="comment">//   Names are wide-strings,</span>
<span class="comment">//   Default memory management algorithm(rbtree_best_fit with no mutexes)</span>
<span class="comment">//   Name-object mappings are stored in the default index type (flat_map)</span>
<span class="keyword">typedef</span> <span class="identifier">basic_managed_mapped_file</span><span class="special">&lt;</span>
   <span class="keyword">wchar_t</span><span class="special">,</span>
   <span class="identifier">rbtree_best_fit</span><span class="special">&lt;</span><span class="identifier">mutex_family</span><span class="special">,</span> <span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="special">&gt;,</span>
   <span class="identifier">flat_map_index</span>
   <span class="special">&gt;</span>  <span class="identifier">wmanaged_mapped_file</span><span class="special">;</span>
</pre>
<p>
          <code class="computeroutput"><span class="identifier">managed_mapped_file</span></code> allocates
          objects in a memory mapped files associated with a c-string and <code class="computeroutput"><span class="identifier">wmanaged_mapped_file</span></code> allocates objects
          in a memory mapped file associated with a wchar_t null terminated string.
          Both define the pointer type as <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span></code> so they can be used to map the file
          at different base addresses in different processes.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_mapped_files.constructing_managed_mapped_files"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_mapped_files.constructing_managed_mapped_files" title="Constructing Managed Mapped Files">Constructing
        Managed Mapped Files</a>
</h4></div></div></div>
<p>
          Managed mapped file is an advanced class that combines a file and a mapped
          region that covers all the file. That means that when we <span class="bold"><strong>create</strong></span>
          a new managed mapped file:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              A new file is created.
            </li>
<li class="listitem">
              The whole file is mapped in the process' address space.
            </li>
<li class="listitem">
              Some helper objects are constructed (name-object index, internal synchronization
              objects, internal variables...) in the mapped region to implement managed
              memory segment features.
            </li>
</ul></div>
<p>
          When we <span class="bold"><strong>open</strong></span> a managed mapped file
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              A file is opened.
            </li>
<li class="listitem">
              The whole file is mapped in the process' address space.
            </li>
</ul></div>
<p>
          To use a managed mapped file, you must include the following header:
        </p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_mapped_file</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<pre class="programlisting"><span class="comment">//1.  Creates a new file</span>
<span class="comment">//    called "MyMappedFile".</span>
<span class="comment">//2.  Maps the whole file to this</span>
<span class="comment">//    process' address space.</span>
<span class="comment">//3.  Constructs some objects in the memory mapped</span>
<span class="comment">//    file to implement managed features.</span>
<span class="comment">//!!  If anything fails, throws interprocess_exception</span>
<span class="comment">//</span>
<span class="identifier">managed_mapped_file</span> <span class="identifier">mfile</span>      <span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span>      <span class="string">"MyMappedFile"</span><span class="special">,</span>   <span class="comment">//Mapped file name      65536);           //Mapped file size</span>
</pre>
<pre class="programlisting"><span class="comment">//1.  Opens a file</span>
<span class="comment">//    called "MyMappedFile".</span>
<span class="comment">//2.  Maps the whole file to this</span>
<span class="comment">//    process' address space.</span>
<span class="comment">//3.  Obtains pointers to constructed internal objects</span>
<span class="comment">//    to implement managed features.</span>
<span class="comment">//!!  If anything fails, throws interprocess_exception</span>
<span class="comment">//</span>
<span class="identifier">managed_mapped_file</span> <span class="identifier">mfile</span>      <span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span>      <span class="string">"MyMappedFile"</span><span class="special">);</span>  <span class="comment">//Mapped file name[c++]</span>

<span class="comment">//1.  If the file was previously created</span>
<span class="comment">//    equivalent to "open_only".</span>
<span class="comment">//2.  Otherwise, equivalent to "open_only" (size is ignored)</span>
<span class="comment">//</span>
<span class="comment">//!!  If anything fails, throws interprocess_exception</span>
<span class="comment">//</span>
<span class="identifier">managed_mapped_file</span> <span class="identifier">mfile</span>      <span class="special">(</span><span class="identifier">open_or_create</span><span class="special">,</span>      <span class="string">"MyMappedFile"</span><span class="special">,</span>   <span class="comment">//Mapped file name      65536);           //Mapped file size</span>
</pre>
<p>
          When the <code class="computeroutput"><span class="identifier">managed_mapped_file</span></code>
          object is destroyed, the file is automatically unmapped, and all the resources
          are freed. To remove the file from the filesystem you could use standard
          C <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">remove</span></code> or <span class="bold"><strong>Boost.Filesystem</strong></span>'s
          <code class="computeroutput"><span class="identifier">remove</span><span class="special">()</span></code>
          functions, but file removing might fail if any process still has the file
          mapped in memory or the file is open by any process.
        </p>
<p>
          To obtain a more portable behaviour, use <code class="computeroutput"><span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*)</span></code>
          operation, which will remove the file even if it's being mapped. However,
          removal will fail in some OS systems if the file (eg. by C++ file streams)
          and no delete share permission was granted to the file. But in most common
          cases <code class="computeroutput"><span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span></code> is portable enough.
        </p>
</div>
<p>
        For more information about managed mapped file capabilities, see <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_managed_mapped_file.html" title="Class template basic_managed_mapped_file">basic_managed_mapped_file</a></code>
        class reference.
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_features"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features" title="Managed Memory Segment Features">Managed
      Memory Segment Features</a>
</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.allocate_deallocate">Allocating
        fragments of a managed memory segment</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.segment_offset">Obtaining
        handles to identify data</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.allocation_types">Object
        construction function family</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.anonymous">Anonymous
        instance construction</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.unique">Unique
        instance construction</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.synchronization">Synchronization
        guarantees</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.index_types">Index
        types for name/object mappings</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_segment_manager">Segment
        Manager</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_information">Obtaining
        information about a constructed object</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_atomic_func">Executing
        an object function atomically</a></span></dt>
</dl></div>
<p>
        The following features are common to all managed memory segment classes,
        but we will use managed shared memory in our examples. We can do the same
        with memory mapped files or other managed memory segment classes.
      </p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_features.allocate_deallocate"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.allocate_deallocate" title="Allocating fragments of a managed memory segment">Allocating
        fragments of a managed memory segment</a>
</h4></div></div></div>
<p>
          If a basic raw-byte allocation is needed from a managed memory segment,
          (for example, a managed shared memory), to implement top-level interprocess
          communications, this class offers <span class="bold"><strong>allocate</strong></span>
          and <span class="bold"><strong>deallocate</strong></span> functions. The allocation
          function comes with throwing and no throwing versions. Throwing version
          throws boost::interprocess::bad_alloc (which derives from <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">bad_alloc</span></code>) if there is no more memory
          and the non-throwing version returns 0 pointer.
        </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>

<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
   <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>

   <span class="comment">//Remove shared memory on construction and destruction</span>
   <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
   <span class="special">{</span>
      <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
      <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
   <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>

   <span class="comment">//Managed memory segment that allocates portions of a shared memory</span>
   <span class="comment">//segment with the default management algorithm</span>
   <span class="identifier">managed_shared_memory</span> <span class="identifier">managed_shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span><span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span>

   <span class="comment">//Allocate 100 bytes of memory from segment, throwing version</span>
   <span class="keyword">void</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">100</span><span class="special">);</span>

   <span class="comment">//Deallocate it</span>
   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span>

   <span class="comment">//Non throwing version</span>
   <span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">100</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow</span><span class="special">);</span>

   <span class="comment">//Deallocate it</span>
   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span>
   <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_features.segment_offset"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.segment_offset" title="Obtaining handles to identify data">Obtaining
        handles to identify data</a>
</h4></div></div></div>
<p>
          The class also offers conversions between absolute addresses that belong
          to a managed memory segment and a handle that can be passed using any interprocess
          mechanism. That handle can be transformed again to an absolute address
          using a managed memory segment that also contains that object. Handles
          can be used as keys between processes to identify allocated portions of
          a managed memory segment or objects constructed in the managed segment.
        </p>
<pre class="programlisting"><span class="comment">//Process A obtains the offset of the address</span>
<span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">handle</span> <span class="identifier">handle</span> <span class="special">=</span>
   <span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_handle_from_address</span><span class="special">(</span><span class="identifier">processA_address</span><span class="special">);</span>

<span class="comment">//Process A sends this address using any mechanism to process B</span>

<span class="comment">//Process B obtains the handle and transforms it again to an address</span>
<span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">handle</span> <span class="identifier">handle</span> <span class="special">=</span> <span class="special">...</span>
<span class="keyword">void</span> <span class="special">*</span> <span class="identifier">processB_address</span> <span class="special">=</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_address_from_handle</span><span class="special">(</span><span class="identifier">handle</span><span class="special">);</span>
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_features.allocation_types"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.allocation_types" title="Object construction function family">Object
        construction function family</a>
</h4></div></div></div>
<p>
          When constructing objects in a managed memory segment (managed shared memory,
          managed mapped files...) associated with a name, the user has a varied
          object construction family to "construct" or to "construct
          if not found". <span class="bold"><strong>Boost.Interprocess</strong></span>
          can construct a single object or an array of objects. The array can be
          constructed with the same parameters for all objects or we can define each
          parameter from a list of iterators:
        </p>
<pre class="programlisting"><span class="comment">//!Allocates and constructs an object of type MyType (throwing version)</span>
<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="string">"Name"</span><span class="special">)</span> <span class="special">(</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span>

<span class="comment">//!Allocates and constructs an array of objects of type MyType (throwing version)</span>
<span class="comment">//!Each object receives the same parameters (par1, par2, ...)</span>
<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="string">"Name"</span><span class="special">)[</span><span class="identifier">count</span><span class="special">](</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span>

<span class="comment">//!Tries to find a previously created object. If not present, allocates</span>
<span class="comment">//!and constructs an object of type MyType (throwing version)</span>
<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">find_or_construct</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="string">"Name"</span><span class="special">)</span> <span class="special">(</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span>

<span class="comment">//!Tries to find a previously created object. If not present, allocates and</span>
<span class="comment">//!constructs an array of objects of type MyType (throwing version). Each object</span>
<span class="comment">//!receives the same parameters (par1, par2, ...)</span>
<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">find_or_construct</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="string">"Name"</span><span class="special">)[</span><span class="identifier">count</span><span class="special">](</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span>

<span class="comment">//!Allocates and constructs an array of objects of type MyType (throwing version)</span>
<span class="comment">//!Each object receives parameters returned with the expression (*it1++, *it2++,... )</span>
<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct_it</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="string">"Name"</span><span class="special">)[</span><span class="identifier">count</span><span class="special">](</span><span class="identifier">it1</span><span class="special">,</span> <span class="identifier">it2</span><span class="special">...);</span>

<span class="comment">//!Tries to find a previously created object. If not present, allocates and constructs</span>
<span class="comment">//!an array of objects of type MyType (throwing version).  Each object receives</span>
<span class="comment">//!parameters returned with the expression (*it1++, *it2++,... )</span>
<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">find_or_construct_it</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="string">"Name"</span><span class="special">)[</span><span class="identifier">count</span><span class="special">](</span><span class="identifier">it1</span><span class="special">,</span> <span class="identifier">it2</span><span class="special">...);</span>

<span class="comment">//!Tries to find a previously created object. Returns a pointer to the object and the</span>
<span class="comment">//!count (if it is not an array, returns 1). If not present, the returned pointer is 0</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="identifier">MyType</span> <span class="special">*,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span> <span class="identifier">ret</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="string">"Name"</span><span class="special">);</span>

<span class="comment">//!Destroys the created object, returns false if not present</span>
<span class="keyword">bool</span> <span class="identifier">destroyed</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">destroy</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="string">"Name"</span><span class="special">);</span>

<span class="comment">//!Destroys the created object via pointer</span>
<span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span>
</pre>
<p>
          All these functions have a non-throwing version, that is invoked with an
          additional parameter std::nothrow. For example, for simple object construction:
        </p>
<pre class="programlisting"><span class="comment">//!Allocates and constructs an object of type MyType (no throwing version)</span>
<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="string">"Name"</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow</span><span class="special">)</span> <span class="special">(</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span>
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_features.anonymous"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.anonymous" title="Anonymous instance construction">Anonymous
        instance construction</a>
</h4></div></div></div>
<p>
          Sometimes, the user doesn't want to create class objects associated with
          a name. For this purpose, <span class="bold"><strong>Boost.Interprocess</strong></span>
          can create anonymous objects in a managed memory segment. All named object
          construction functions are available to construct anonymous objects. To
          allocate an anonymous objects, the user must use "boost::interprocess::anonymous_instance"
          name instead of a normal name:
        </p>
<pre class="programlisting"><span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="identifier">anonymous_instance</span><span class="special">)</span> <span class="special">(</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span>

<span class="comment">//Other construct variants can also be used (including non-throwing ones)</span>
<span class="special">...</span>

<span class="comment">//We can only destroy the anonymous object via pointer</span>
<span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span>
</pre>
<p>
          Find functions have no sense here, since anonymous objects have no name.
          We can only destroy the anonymous object via pointer.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_features.unique"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.unique" title="Unique instance construction">Unique
        instance construction</a>
</h4></div></div></div>
<p>
          Sometimes, the user wants to emulate a singleton in a managed memory segment.
          Obviously, as the managed memory segment is constructed at run-time, the
          user must construct and destroy this object explicitly. But how can the
          user be sure that the object is the only object of its type in the managed
          memory segment? This can be emulated using a named object and checking
          if it is present before trying to create one, but all processes must agree
          in the object's name, that can also conflict with other existing names.
        </p>
<p>
          To solve this, <span class="bold"><strong>Boost.Interprocess</strong></span> offers
          a "unique object" creation in a managed memory segment. Only
          one instance of a class can be created in a managed memory segment using
          this "unique object" service (you can create more named objects
          of this class, though) so it makes easier the emulation of singleton-like
          objects across processes, for example, to design pooled, shared memory
          allocators. The object can be searched using the type of the class as a
          key.
        </p>
<pre class="programlisting"><span class="comment">// Construct</span>
<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="identifier">unique_instance</span><span class="special">)</span> <span class="special">(</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span>

<span class="comment">// Find it</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="identifier">MyType</span> <span class="special">*,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span> <span class="identifier">ret</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="identifier">unique_instance</span><span class="special">);</span>

<span class="comment">// Destroy it</span>
<span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">destroy</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="identifier">unique_instance</span><span class="special">);</span>

<span class="comment">// Other construct and find variants can also be used (including non-throwing ones)</span>
<span class="comment">//...</span>
</pre>
<pre class="programlisting"><span class="comment">// We can also destroy the unique object via pointer</span>
<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="identifier">unique_instance</span><span class="special">)</span> <span class="special">(</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span>
<span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span>
</pre>
<p>
          The find function obtains a pointer to the only object of type T that can
          be created using this "unique instance" mechanism.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_features.synchronization"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.synchronization" title="Synchronization guarantees">Synchronization
        guarantees</a>
</h4></div></div></div>
<p>
          One of the features of named/unique allocations/searches/destructions is
          that they are <span class="bold"><strong>atomic</strong></span>. Named allocations
          use the recursive synchronization scheme defined by the internal <code class="computeroutput"><span class="identifier">mutex_family</span></code> typedef defined of the memory
          allocation algorithm template parameter (<code class="computeroutput"><span class="identifier">MemoryAlgorithm</span></code>).
          That is, the mutex type used to synchronize named/unique allocations is
          defined by the <code class="computeroutput"><span class="identifier">MemoryAlgorithm</span><span class="special">::</span><span class="identifier">mutex_family</span><span class="special">::</span><span class="identifier">recursive_mutex_type</span></code>
          type. For shared memory, and memory mapped file based managed segments
          this recursive mutex is defined as <code class="computeroutput"><a class="link" href="../boost/interprocess/interprocess_r_idp28519592.html" title="Class interprocess_recursive_mutex">interprocess_recursive_mutex</a></code>.
        </p>
<p>
          If two processes can call:
        </p>
<pre class="programlisting"><span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">find_or_construct</span><span class="special">&lt;</span><span class="identifier">MyType</span><span class="special">&gt;(</span><span class="string">"Name"</span><span class="special">)[</span><span class="identifier">count</span><span class="special">](</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span>
</pre>
<p>
          at the same time, but only one process will create the object and the other
          will obtain a pointer to the created object.
        </p>
<p>
          Raw allocation using <code class="computeroutput"><span class="identifier">allocate</span><span class="special">()</span></code> can be called also safely while executing
          named/anonymous/unique allocations, just like when programming a multithreaded
          application inserting an object in a mutex-protected map does not block
          other threads from calling new[] while the map thread is searching the
          place where it has to insert the new object. The synchronization does happen
          once the map finds the correct place and it has to allocate raw memory
          to construct the new value.
        </p>
<p>
          This means that if we are creating or searching for a lot of named objects,
          we only block creation/searches from other processes but we don't block
          another process if that process is inserting elements in a shared memory
          vector.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_features.index_types"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.index_types" title="Index types for name/object mappings">Index
        types for name/object mappings</a>
</h4></div></div></div>
<p>
          As seen, managed memory segments, when creating named objects, store the
          name/object association in an index. The index is a map with the name of
          the object as a key and a pointer to the object as the mapped type. The
          default specializations, <span class="bold"><strong>managed_shared_memory</strong></span>
          and <span class="bold"><strong>wmanaged_shared_memory</strong></span>, use <span class="bold"><strong>flat_map_index</strong></span> as the index type.
        </p>
<p>
          Each index has its own characteristics, like search-time, insertion time,
          deletion time, memory use, and memory allocation patterns. <span class="bold"><strong>Boost.Interprocess</strong></span>
          offers 3 index types right now:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              <span class="bold"><strong>boost::interprocess::flat_map_index flat_map_index</strong></span>:
              Based on boost::interprocess::flat_map, an ordered vector similar to
              Loki library's AssocVector class, offers great search time and minimum
              memory use. But the vector must be reallocated when is full, so all
              data must be copied to the new buffer. Ideal when insertions are mainly
              in initialization time and in run-time we just need searches.
            </li>
<li class="listitem">
              <span class="bold"><strong>boost::interprocess::map_index map_index</strong></span>:
              Based on boost::interprocess::map, a managed memory ready version of
              std::map. Since it's a node based container, it has no reallocations,
              the tree must be just rebalanced sometimes. Offers equilibrated insertion/deletion/search
              times with more overhead per node comparing to <span class="bold"><strong>boost::interprocess::flat_map_index</strong></span>.
              Ideal when searches/insertions/deletions are in random order.
            </li>
<li class="listitem">
              <span class="bold"><strong>boost::interprocess::null_index null_index</strong></span>:
              This index is for people using a managed memory segment just for raw
              memory buffer allocations and they don't make use of named/unique allocations.
              This class is just empty and saves some space and compilation time.
              If you try to use named object creation with a managed memory segment
              using this index, you will get a compilation error.
            </li>
</ul></div>
<p>
          As an example, if we want to define new managed shared memory class using
          <span class="bold"><strong>boost::interprocess::map</strong></span> as the index
          type we just must specify [boost::interprocess::map_index map_index] as
          a template parameter:
        </p>
<pre class="programlisting"><span class="comment">//This managed memory segment can allocate objects with:</span>
<span class="comment">// -&gt; a wchar_t string as key</span>
<span class="comment">// -&gt; boost::interprocess::rbtree_best_fit with process-shared mutexes</span>
<span class="comment">//       as memory allocation algorithm.</span>
<span class="comment">// -&gt; boost::interprocess::map&lt;...&gt; as the index to store name/object mappings</span>
<span class="comment">//</span>
<span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">basic_managed_shared_memory</span>
         <span class="special">&lt;</span>  <span class="keyword">wchar_t</span>
         <span class="special">,</span>  <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">rbtree_best_fit</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">mutex_family</span><span class="special">,</span> <span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="special">&gt;</span>
         <span class="special">,</span>  <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">map_index</span>
         <span class="special">&gt;</span>  <span class="identifier">my_managed_shared_memory</span><span class="special">;</span>
</pre>
<p>
          <span class="bold"><strong>Boost.Interprocess</strong></span> plans to offer an
          <span class="bold"><strong>unordered_map</strong></span> based index as soon as this
          container is included in Boost. If these indexes are not enough for you,
          you can define your own index type. To know how to do this, go to <a class="link" href="customizing_interprocess.html#interprocess.customizing_interprocess.custom_indexes" title="Building custom indexes">Building
          custom indexes</a> section.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_segment_manager"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_segment_manager" title="Segment Manager">Segment
        Manager</a>
</h4></div></div></div>
<p>
          All <span class="bold"><strong>Boost.Interprocess</strong></span> managed memory
          segment classes construct in their respective memory segments (shared memory,
          memory mapped files, heap memory...) some structures to implement the memory
          management algorithm, named allocations, synchronization objects... All
          these objects are encapsulated in a single object called <span class="bold"><strong>segment
          manager</strong></span>. A managed memory mapped file and a managed shared memory
          use the same <span class="bold"><strong>segment manager</strong></span> to implement
          all managed memory segment features, due to the fact that a <span class="bold"><strong>segment
          manager</strong></span> is a class that manages a fixed size memory buffer.
          Since both shared memory or memory mapped files are accessed though a mapped
          region, and a mapped region is a fixed size memory buffer, a single <span class="bold"><strong>segment manager</strong></span> class can manage several managed
          memory segment types.
        </p>
<p>
          Some <span class="bold"><strong>Boost.Interprocess</strong></span> classes require
          a pointer to the segment manager in their constructors, and the segment
          manager can be obtained from any managed memory segment using <code class="computeroutput"><span class="identifier">get_segment_manager</span></code> member:
        </p>
<pre class="programlisting"><span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span> <span class="special">*</span><span class="identifier">seg_manager</span> <span class="special">=</span>
   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">();</span>
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_information"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_information" title="Obtaining information about a constructed object">Obtaining
        information about a constructed object</a>
</h4></div></div></div>
<p>
          Once an object is constructed using <code class="computeroutput"><span class="identifier">construct</span><span class="special">&lt;&gt;</span></code> function family, the programmer
          can obtain information about the object using a pointer to the object.
          The programmer can obtain the following information:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              Name of the object: If it's a named instance, the name used in the
              construction function is returned, otherwise 0 is returned.
            </li>
<li class="listitem">
              Length of the object: Returns the number of elements of the object
              (1 if it's a single value, &gt;=1 if it's an array).
            </li>
<li class="listitem">
              The type of construction: Whether the object was constructed using
              a named, unique or anonymous construction.
            </li>
</ul></div>
<p>
          Here is an example showing this functionality:
        </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cstring</span><span class="special">&gt;</span>

<span class="keyword">class</span> <span class="identifier">my_class</span>
<span class="special">{</span>
   <span class="comment">//...</span>
<span class="special">};</span>

<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
   <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>

   <span class="comment">//Remove shared memory on construction and destruction</span>
   <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
   <span class="special">{</span>
      <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
      <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
   <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>

   <span class="identifier">managed_shared_memory</span> <span class="identifier">managed_shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">10000</span><span class="special">*</span><span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">));</span>

   <span class="comment">//Construct objects</span>
   <span class="identifier">my_class</span> <span class="special">*</span><span class="identifier">named_object</span>  <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">my_class</span><span class="special">&gt;(</span><span class="string">"Object name"</span><span class="special">)[</span><span class="number">1</span><span class="special">]();</span>
   <span class="identifier">my_class</span> <span class="special">*</span><span class="identifier">unique_object</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">my_class</span><span class="special">&gt;(</span><span class="identifier">unique_instance</span><span class="special">)[</span><span class="number">2</span><span class="special">]();</span>
   <span class="identifier">my_class</span> <span class="special">*</span><span class="identifier">anon_object</span>   <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">my_class</span><span class="special">&gt;(</span><span class="identifier">anonymous_instance</span><span class="special">)[</span><span class="number">3</span><span class="special">]();</span>

   <span class="comment">//Now test "get_instance_name" function.</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="number">0</span> <span class="special">==</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">strcmp</span><span class="special">(</span><span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_name</span><span class="special">(</span><span class="identifier">named_object</span><span class="special">),</span> <span class="string">"Object name"</span><span class="special">));</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="number">0</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_name</span><span class="special">(</span><span class="identifier">unique_object</span><span class="special">));</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="number">0</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_name</span><span class="special">(</span><span class="identifier">anon_object</span><span class="special">));</span>

   <span class="comment">//Now test "get_instance_type" function.</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">named_type</span>     <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_type</span><span class="special">(</span><span class="identifier">named_object</span><span class="special">));</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_type</span>    <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_type</span><span class="special">(</span><span class="identifier">unique_object</span><span class="special">));</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">anonymous_type</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_type</span><span class="special">(</span><span class="identifier">anon_object</span><span class="special">));</span>

   <span class="comment">//Now test "get_instance_length" function.</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="number">1</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_length</span><span class="special">(</span><span class="identifier">named_object</span><span class="special">));</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="number">2</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_length</span><span class="special">(</span><span class="identifier">unique_object</span><span class="special">));</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="number">3</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_length</span><span class="special">(</span><span class="identifier">anon_object</span><span class="special">));</span>

   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">named_object</span><span class="special">);</span>
   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">unique_object</span><span class="special">);</span>
   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">anon_object</span><span class="special">);</span>
   <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_atomic_func"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_atomic_func" title="Executing an object function atomically">Executing
        an object function atomically</a>
</h4></div></div></div>
<p>
          Sometimes the programmer must execute some code, and needs to execute it
          with the guarantee that no other process or thread will create or destroy
          any named, unique or anonymous object while executing the functor. A user
          might want to create several named objects and initialize them, but those
          objects should be available for the rest of processes at once.
        </p>
<p>
          To achieve this, the programmer can use the <code class="computeroutput"><span class="identifier">atomic_func</span><span class="special">()</span></code> function offered by managed classes:
        </p>
<pre class="programlisting"><span class="comment">//This object function will create several named objects</span>
<span class="identifier">create_several_objects_func</span> <span class="identifier">func</span><span class="special">(/**/);</span>

<span class="comment">//While executing the function, no other process will be</span>
<span class="comment">//able to create or destroy objects</span>
<span class="identifier">managed_memory</span><span class="special">.</span><span class="identifier">atomic_func</span><span class="special">(</span><span class="identifier">func</span><span class="special">);</span>
</pre>
<p>
          Note that <code class="computeroutput"><span class="identifier">atomic_func</span></code> does
          not prevent other processes from allocating raw memory or executing member
          functions for already constructed objects (e.g.: another process might
          be pushing elements into a vector placed in the segment). The atomic function
          only blocks named, unique and anonymous creation, search and destruction
          (concurrent calls to <code class="computeroutput"><span class="identifier">construct</span><span class="special">&lt;&gt;</span></code>, <code class="computeroutput"><span class="identifier">find</span><span class="special">&lt;&gt;</span></code>, <code class="computeroutput"><span class="identifier">find_or_construct</span><span class="special">&lt;&gt;</span></code>, <code class="computeroutput"><span class="identifier">destroy</span><span class="special">&lt;&gt;</span></code>...) from other processes.
        </p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features" title="Managed Memory Segment Advanced Features">Managed
      Memory Segment Advanced Features</a>
</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_information">Obtaining
        information about the managed segment</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.growing_managed_memory">Growing
        managed segments</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_advanced_index_functions">Advanced
        index functions</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.allocate_aligned">Allocating
        aligned memory portions</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_multiple_allocations">Multiple
        allocation functions</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_expand_in_place">Expand
        in place memory allocation</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.copy_on_write_read_only">Opening
        managed shared memory and mapped files with Copy On Write or Read Only modes</a></span></dt>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_information"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_information" title="Obtaining information about the managed segment">Obtaining
        information about the managed segment</a>
</h4></div></div></div>
<p>
          These functions are available to obtain information about the managed memory
          segments:
        </p>
<p>
          Obtain the size of the memory segment:
        </p>
<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">();</span>
</pre>
<p>
          Obtain the number of free bytes of the segment:
        </p>
<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_free_memory</span><span class="special">();</span>
</pre>
<p>
          Clear to zero the free memory:
        </p>
<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">zero_free_memory</span><span class="special">();</span>
</pre>
<p>
          Know if all memory has been deallocated, false otherwise:
        </p>
<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">all_memory_deallocated</span><span class="special">();</span>
</pre>
<p>
          Test internal structures of the managed segment. Returns true if no errors
          are detected:
        </p>
<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">check_sanity</span><span class="special">();</span>
</pre>
<p>
          Obtain the number of named and unique objects allocated in the segment:
        </p>
<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_num_named_objects</span><span class="special">();</span>
<span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_num_unique_objects</span><span class="special">();</span>
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.growing_managed_memory"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.growing_managed_memory" title="Growing managed segments">Growing
        managed segments</a>
</h4></div></div></div>
<p>
          Once a managed segment is created the managed segment can't be grown. The
          limitation is not easily solvable: every process attached to the managed
          segment would need to be stopped, notified of the new size, they would
          need to remap the managed segment and continue working. Nearly impossible
          to achieve with a user-level library without the help of the operating
          system kernel.
        </p>
<p>
          On the other hand, <span class="bold"><strong>Boost.Interprocess</strong></span>
          offers off-line segment growing. What does this mean? That the segment
          can be grown if no process has mapped the managed segment. If the application
          can find a moment where no process is attached it can grow or shrink to
          fit the managed segment.
        </p>
<p>
          Here we have an example showing how to grow and shrink to fit <code class="computeroutput"><a class="link" href="indexes_reference.html#boost.interprocess.managed_shared_memory">managed_shared_memory</a></code>:
        </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_mapped_file</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>

<span class="keyword">class</span> <span class="identifier">MyClass</span>
<span class="special">{</span>
   <span class="comment">//...</span>
<span class="special">};</span>

<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
   <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
   <span class="comment">//Remove shared memory on construction and destruction</span>
   <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
   <span class="special">{</span>
      <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
      <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
   <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>

   <span class="special">{</span>
      <span class="comment">//Create a managed shared memory</span>
      <span class="identifier">managed_shared_memory</span> <span class="identifier">shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">1000</span><span class="special">);</span>

      <span class="comment">//Check size</span>
      <span class="identifier">assert</span><span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">()</span> <span class="special">==</span> <span class="number">1000</span><span class="special">);</span>
      <span class="comment">//Construct a named object</span>
      <span class="identifier">MyClass</span> <span class="special">*</span><span class="identifier">myclass</span> <span class="special">=</span> <span class="identifier">shm</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">&gt;(</span><span class="string">"MyClass"</span><span class="special">)();</span>
      <span class="comment">//The managed segment is unmapped here</span>
   <span class="special">}</span>
   <span class="special">{</span>
      <span class="comment">//Now that the segment is not mapped grow it adding extra 500 bytes</span>
      <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">grow</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">500</span><span class="special">);</span>

      <span class="comment">//Map it again</span>
      <span class="identifier">managed_shared_memory</span> <span class="identifier">shm</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">);</span>
      <span class="comment">//Check size</span>
      <span class="identifier">assert</span><span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">()</span> <span class="special">==</span> <span class="number">1500</span><span class="special">);</span>
      <span class="comment">//Check "MyClass" is still there</span>
      <span class="identifier">MyClass</span> <span class="special">*</span><span class="identifier">myclass</span> <span class="special">=</span> <span class="identifier">shm</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">&gt;(</span><span class="string">"MyClass"</span><span class="special">).</span><span class="identifier">first</span><span class="special">;</span>
      <span class="identifier">assert</span><span class="special">(</span><span class="identifier">myclass</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span>
      <span class="comment">//The managed segment is unmapped here</span>
   <span class="special">}</span>
   <span class="special">{</span>
      <span class="comment">//Now minimize the size of the segment</span>
      <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">shrink_to_fit</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span>

      <span class="comment">//Map it again</span>
      <span class="identifier">managed_shared_memory</span> <span class="identifier">shm</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">);</span>
      <span class="comment">//Check size</span>
      <span class="identifier">assert</span><span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">()</span> <span class="special">&lt;</span> <span class="number">1000</span><span class="special">);</span>
      <span class="comment">//Check "MyClass" is still there</span>
      <span class="identifier">MyClass</span> <span class="special">*</span><span class="identifier">myclass</span> <span class="special">=</span> <span class="identifier">shm</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">&gt;(</span><span class="string">"MyClass"</span><span class="special">).</span><span class="identifier">first</span><span class="special">;</span>
      <span class="identifier">assert</span><span class="special">(</span><span class="identifier">myclass</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span>
      <span class="comment">//The managed segment is unmapped here</span>
   <span class="special">}</span>
   <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
        </p>
<p>
          <code class="computeroutput"><a class="link" href="indexes_reference.html#boost.interprocess.managed_mapped_file">managed_mapped_file</a></code>
          also offers a similar function to grow or shrink_to_fit the managed file.
          Please, remember that <span class="bold"><strong>no process should be modifying
          the file/shared memory while the growing/shrinking process is performed</strong></span>.
          Otherwise, the managed segment will be corrupted.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_advanced_index_functions"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_advanced_index_functions" title="Advanced index functions">Advanced
        index functions</a>
</h4></div></div></div>
<p>
          As mentioned, the managed segment stores the information about named and
          unique objects in two indexes. Depending on the type of those indexes,
          the index must reallocate some auxiliary structures when new named or unique
          allocations are made. For some indexes, if the user knows how many named
          or unique objects are going to be created it's possible to preallocate
          some structures to obtain much better performance. (If the index is an
          ordered vector it can preallocate memory to avoid reallocations. If the
          index is a hash structure it can preallocate the bucket array).
        </p>
<p>
          The following functions reserve memory to make the subsequent allocation
          of named or unique objects more efficient. These functions are only useful
          for pseudo-intrusive or non-node indexes (like <code class="computeroutput"><span class="identifier">flat_map_index</span></code>,
          <code class="computeroutput"><span class="identifier">iunordered_set_index</span></code>).
          These functions have no effect with the default index (<code class="computeroutput"><span class="identifier">iset_index</span></code>)
          or other indexes (<code class="computeroutput"><span class="identifier">map_index</span></code>):
        </p>
<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">reserve_named_objects</span><span class="special">(</span><span class="number">1000</span><span class="special">);</span>
<span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">reserve_unique_objects</span><span class="special">(</span><span class="number">1000</span><span class="special">);</span>
</pre>
<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">reserve_named_objects</span><span class="special">(</span><span class="number">1000</span><span class="special">);</span>
<span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">reserve_unique_objects</span><span class="special">(</span><span class="number">1000</span><span class="special">);</span>
</pre>
<p>
          Managed memory segments also offer the possibility to iterate through constructed
          named and unique objects for debugging purposes. <span class="bold"><strong>Caution:
          this iteration is not thread-safe</strong></span> so the user should make sure
          that no other thread is manipulating named or unique indexes (creating,
          erasing, reserving...) in the segment. Other operations not involving indexes
          can be concurrently executed (raw memory allocation/deallocations, for
          example).
        </p>
<p>
          The following functions return constant iterators to the range of named
          and unique objects stored in the managed segment. Depending on the index
          type, iterators might be invalidated after a named or unique creation/erasure/reserve
          operation:
        </p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">const_named_iterator</span> <span class="identifier">const_named_it</span><span class="special">;</span>
<span class="identifier">const_named_it</span> <span class="identifier">named_beg</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">named_begin</span><span class="special">();</span>
<span class="identifier">const_named_it</span> <span class="identifier">named_end</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">named_end</span><span class="special">();</span>

<span class="keyword">typedef</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">const_unique_iterator</span> <span class="identifier">const_unique_it</span><span class="special">;</span>
<span class="identifier">const_unique_it</span> <span class="identifier">unique_beg</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">unique_begin</span><span class="special">();</span>
<span class="identifier">const_unique_it</span> <span class="identifier">unique_end</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">unique_end</span><span class="special">();</span>

<span class="keyword">for</span><span class="special">(;</span> <span class="identifier">named_beg</span> <span class="special">!=</span> <span class="identifier">named_end</span><span class="special">;</span> <span class="special">++</span><span class="identifier">named_beg</span><span class="special">){</span>
   <span class="comment">//A pointer to the name of the named object</span>
   <span class="keyword">const</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">char_type</span> <span class="special">*</span><span class="identifier">name</span> <span class="special">=</span> <span class="identifier">named_beg</span><span class="special">-&gt;</span><span class="identifier">name</span><span class="special">();</span>
   <span class="comment">//The length of the name</span>
   <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">name_len</span> <span class="special">=</span> <span class="identifier">named_beg</span><span class="special">-&gt;</span><span class="identifier">name_length</span><span class="special">();</span>
   <span class="comment">//A constant void pointer to the named object</span>
   <span class="keyword">const</span> <span class="keyword">void</span> <span class="special">*</span><span class="identifier">value</span> <span class="special">=</span> <span class="identifier">named_beg</span><span class="special">-&gt;</span><span class="identifier">value</span><span class="special">();</span>
<span class="special">}</span>

<span class="keyword">for</span><span class="special">(;</span> <span class="identifier">unique_beg</span> <span class="special">!=</span> <span class="identifier">unique_end</span><span class="special">;</span> <span class="special">++</span><span class="identifier">unique_beg</span><span class="special">){</span>
   <span class="comment">//The typeid(T).name() of the unique object</span>
   <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">typeid_name</span> <span class="special">=</span> <span class="identifier">unique_beg</span><span class="special">-&gt;</span><span class="identifier">name</span><span class="special">();</span>
   <span class="comment">//The length of the name</span>
   <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">name_len</span> <span class="special">=</span> <span class="identifier">unique_beg</span><span class="special">-&gt;</span><span class="identifier">name_length</span><span class="special">();</span>
   <span class="comment">//A constant void pointer to the unique object</span>
   <span class="keyword">const</span> <span class="keyword">void</span> <span class="special">*</span><span class="identifier">value</span> <span class="special">=</span> <span class="identifier">unique_beg</span><span class="special">-&gt;</span><span class="identifier">value</span><span class="special">();</span>
<span class="special">}</span>
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.allocate_aligned"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.allocate_aligned" title="Allocating aligned memory portions">Allocating
        aligned memory portions</a>
</h4></div></div></div>
<p>
          Sometimes it's interesting to be able to allocate aligned fragments of
          memory because of some hardware or software restrictions. Sometimes, having
          aligned memory is a feature that can be used to improve several memory
          algorithms.
        </p>
<p>
          This allocation is similar to the previously shown raw memory allocation
          but it takes an additional parameter specifying the alignment. There is
          a restriction for the alignment: <span class="bold"><strong>the alignment must
          be power of two</strong></span>.
        </p>
<p>
          If a user wants to allocate many aligned blocks (for example aligned to
          128 bytes), the size that minimizes the memory waste is a value that's
          is nearly a multiple of that alignment (for example 2*128 - some bytes).
          The reason for this is that every memory allocation usually needs some
          additional metadata in the first bytes of the allocated buffer. If the
          user can know the value of "some bytes" and if the first bytes
          of a free block of memory are used to fulfill the aligned allocation, the
          rest of the block can be left also aligned and ready for the next aligned
          allocation. Note that requesting <span class="bold"><strong>a size multiple
          of the alignment is not optimal</strong></span> because lefts the next block
          of memory unaligned due to the needed metadata.
        </p>
<p>
          Once the programmer knows the size of the payload of every memory allocation,
          he can request a size that will be optimal to allocate aligned chunks of
          memory maximizing both the size of the request <span class="bold"><strong>and</strong></span>
          the possibilities of future aligned allocations. This information is stored
          in the PayloadPerAllocation constant of managed memory segments.
        </p>
<p>
          Here is a small example showing how aligned allocation is used:
        </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>

<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
   <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>

   <span class="comment">//Remove shared memory on construction and destruction</span>
   <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
   <span class="special">{</span>
      <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
      <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
   <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>

   <span class="comment">//Managed memory segment that allocates portions of a shared memory</span>
   <span class="comment">//segment with the default management algorithm</span>
   <span class="identifier">managed_shared_memory</span> <span class="identifier">managed_shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span>

   <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">Alignment</span> <span class="special">=</span> <span class="number">128</span><span class="special">;</span>

   <span class="comment">//Allocate 100 bytes aligned to Alignment from segment, throwing version</span>
   <span class="keyword">void</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate_aligned</span><span class="special">(</span><span class="number">100</span><span class="special">,</span> <span class="identifier">Alignment</span><span class="special">);</span>

   <span class="comment">//Check alignment</span>
   <span class="identifier">assert</span><span class="special">((</span><span class="keyword">static_cast</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">*&gt;(</span><span class="identifier">ptr</span><span class="special">)-</span><span class="keyword">static_cast</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">*&gt;(</span><span class="number">0</span><span class="special">))</span> <span class="special">%</span> <span class="identifier">Alignment</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>

   <span class="comment">//Deallocate it</span>
   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span>

   <span class="comment">//Non throwing version</span>
   <span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate_aligned</span><span class="special">(</span><span class="number">100</span><span class="special">,</span> <span class="identifier">Alignment</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow</span><span class="special">);</span>

   <span class="comment">//Check alignment</span>
   <span class="identifier">assert</span><span class="special">((</span><span class="keyword">static_cast</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">*&gt;(</span><span class="identifier">ptr</span><span class="special">)-</span><span class="keyword">static_cast</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">*&gt;(</span><span class="number">0</span><span class="special">))</span> <span class="special">%</span> <span class="identifier">Alignment</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>

   <span class="comment">//Deallocate it</span>
   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span>

   <span class="comment">//If we want to efficiently allocate aligned blocks of memory</span>
   <span class="comment">//use managed_shared_memory::PayloadPerAllocation value</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">Alignment</span> <span class="special">&gt;</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">PayloadPerAllocation</span><span class="special">);</span>

   <span class="comment">//This allocation will maximize the size of the aligned memory</span>
   <span class="comment">//and will increase the possibility of finding more aligned memory</span>
   <span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate_aligned</span>
      <span class="special">(</span><span class="number">3</span><span class="special">*</span><span class="identifier">Alignment</span> <span class="special">-</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">PayloadPerAllocation</span><span class="special">,</span> <span class="identifier">Alignment</span><span class="special">);</span>

   <span class="comment">//Check alignment</span>
   <span class="identifier">assert</span><span class="special">((</span><span class="keyword">static_cast</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">*&gt;(</span><span class="identifier">ptr</span><span class="special">)-</span><span class="keyword">static_cast</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">*&gt;(</span><span class="number">0</span><span class="special">))</span> <span class="special">%</span> <span class="identifier">Alignment</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>

   <span class="comment">//Deallocate it</span>
   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span>

   <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_multiple_allocations"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_multiple_allocations" title="Multiple allocation functions">Multiple
        allocation functions</a>
</h4></div></div></div>
<div class="caution"><table border="0" summary="Caution">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../doc/src/images/caution.png"></td>
<th align="left">Caution</th>
</tr>
<tr><td align="left" valign="top"><p>
            This feature is experimental, interface and ABI are unstable
          </p></td></tr>
</table></div>
<p>
          If an application needs to allocate a lot of memory buffers but it needs
          to deallocate them independently, the application is normally forced to
          loop calling <code class="computeroutput"><span class="identifier">allocate</span><span class="special">()</span></code>.
          Managed memory segments offer an alternative function to pack several allocations
          in a single call obtaining memory buffers that:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              are packed contiguously in memory (which improves locality)
            </li>
<li class="listitem">
              can be independently deallocated.
            </li>
</ul></div>
<p>
          This allocation method is much faster than calling <code class="computeroutput"><span class="identifier">allocate</span><span class="special">()</span></code> in a loop. The downside is that the segment
          must provide a contiguous memory segment big enough to hold all the allocations.
          Managed memory segments offer this functionality through <code class="computeroutput"><span class="identifier">allocate_many</span><span class="special">()</span></code>
          functions. There are 2 types of <code class="computeroutput"><span class="identifier">allocate_many</span></code>
          functions:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              Allocation of N buffers of memory with the same size.
            </li>
<li class="listitem">
              Allocation ot N buffers of memory, each one of different size.
            </li>
</ul></div>
<pre class="programlisting"><span class="comment">//!Allocates n_elements of elem_bytes bytes. </span>
<span class="comment">//!Throws bad_alloc on failure. chain.size() is not increased on failure.</span>
<span class="keyword">void</span> <span class="identifier">allocate_many</span><span class="special">(</span><span class="identifier">size_type</span> <span class="identifier">elem_bytes</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">n_elements</span><span class="special">,</span> <span class="identifier">multiallocation_chain</span> <span class="special">&amp;</span><span class="identifier">chain</span><span class="special">);</span>

<span class="comment">//!Allocates n_elements, each one of element_lengths[i]*sizeof_element bytes.</span>
<span class="comment">//!Throws bad_alloc on failure. chain.size() is not increased on failure.</span>
<span class="keyword">void</span> <span class="identifier">allocate_many</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">size_type</span> <span class="special">*</span><span class="identifier">element_lengths</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">n_elements</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">sizeof_element</span><span class="special">,</span> <span class="identifier">multiallocation_chain</span> <span class="special">&amp;</span><span class="identifier">chain</span><span class="special">);</span>

<span class="comment">//!Allocates n_elements of elem_bytes bytes. </span>
<span class="comment">//!Non-throwing version. chain.size() is not increased on failure.</span>
<span class="keyword">void</span> <span class="identifier">allocate_many</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow_t</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">elem_bytes</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">n_elements</span><span class="special">,</span> <span class="identifier">multiallocation_chain</span> <span class="special">&amp;</span><span class="identifier">chain</span><span class="special">);</span>

<span class="comment">//!Allocates n_elements, each one of</span>
<span class="comment">//!element_lengths[i]*sizeof_element bytes.</span>
<span class="comment">//!Non-throwing version. chain.size() is not increased on failure.</span>
<span class="keyword">void</span> <span class="identifier">allocate_many</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow_t</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">size_type</span> <span class="special">*</span><span class="identifier">elem_sizes</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">n_elements</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">sizeof_element</span><span class="special">,</span> <span class="identifier">multiallocation_chain</span> <span class="special">&amp;</span><span class="identifier">chain</span><span class="special">);</span>

<span class="comment">//!Deallocates all elements contained in chain.</span>
<span class="comment">//!Never throws.</span>
<span class="keyword">void</span> <span class="identifier">deallocate_many</span><span class="special">(</span><span class="identifier">multiallocation_chain</span> <span class="special">&amp;</span><span class="identifier">chain</span><span class="special">);</span>
</pre>
<p>
          Here is a small example showing all this functionality:
        </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">detail</span><span class="special">/</span><span class="identifier">move</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span> <span class="comment">//boost::move</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;//</span><span class="identifier">assert</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cstring</span><span class="special">&gt;//</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">memset</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="keyword">new</span><span class="special">&gt;</span>    <span class="comment">//std::nothrow</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">vector</span><span class="special">&gt;</span> <span class="comment">//std::vector</span>

<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
   <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">multiallocation_chain</span> <span class="identifier">multiallocation_chain</span><span class="special">;</span>

   <span class="comment">//Remove shared memory on construction and destruction</span>
   <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
   <span class="special">{</span>
      <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
      <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
   <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>

   <span class="identifier">managed_shared_memory</span> <span class="identifier">managed_shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span><span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span>

   <span class="comment">//Allocate 16 elements of 100 bytes in a single call. Non-throwing version.</span>
   <span class="identifier">multiallocation_chain</span> <span class="identifier">chain</span><span class="special">;</span>
   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate_many</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow</span><span class="special">,</span> <span class="number">100</span><span class="special">,</span> <span class="number">16</span><span class="special">,</span> <span class="identifier">chain</span><span class="special">);</span>

   <span class="comment">//Check if the memory allocation was successful</span>
   <span class="keyword">if</span><span class="special">(</span><span class="identifier">chain</span><span class="special">.</span><span class="identifier">empty</span><span class="special">())</span> <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>

   <span class="comment">//Allocated buffers</span>
   <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">*&gt;</span> <span class="identifier">allocated_buffers</span><span class="special">;</span>

   <span class="comment">//Initialize our data</span>
   <span class="keyword">while</span><span class="special">(!</span><span class="identifier">chain</span><span class="special">.</span><span class="identifier">empty</span><span class="special">()){</span>
      <span class="keyword">void</span> <span class="special">*</span><span class="identifier">buf</span> <span class="special">=</span> <span class="identifier">chain</span><span class="special">.</span><span class="identifier">pop_front</span><span class="special">();</span>
      <span class="identifier">allocated_buffers</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">buf</span><span class="special">);</span>
      <span class="comment">//The iterator must be incremented before overwriting memory</span>
      <span class="comment">//because otherwise, the iterator is invalidated.</span>
      <span class="identifier">std</span><span class="special">::</span><span class="identifier">memset</span><span class="special">(</span><span class="identifier">buf</span><span class="special">,</span> <span class="number">0</span><span class="special">,</span> <span class="number">100</span><span class="special">);</span>
   <span class="special">}</span>

   <span class="comment">//Now deallocate</span>
   <span class="keyword">while</span><span class="special">(!</span><span class="identifier">allocated_buffers</span><span class="special">.</span><span class="identifier">empty</span><span class="special">()){</span>
      <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocated_buffers</span><span class="special">.</span><span class="identifier">back</span><span class="special">());</span>
      <span class="identifier">allocated_buffers</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span>
   <span class="special">}</span>

   <span class="comment">//Allocate 10 buffers of different sizes in a single call. Throwing version</span>
   <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">sizes</span><span class="special">[</span><span class="number">10</span><span class="special">];</span>
   <span class="keyword">for</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">&lt;</span> <span class="number">10</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span>
      <span class="identifier">sizes</span><span class="special">[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">*</span><span class="number">3</span><span class="special">;</span>

   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate_many</span><span class="special">(</span><span class="identifier">sizes</span><span class="special">,</span> <span class="number">10</span><span class="special">,</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">chain</span><span class="special">);</span>
   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate_many</span><span class="special">(</span><span class="identifier">chain</span><span class="special">);</span>
   <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
        </p>
<p>
          Allocating N buffers of the same size improves the performance of pools
          and node containers (for example STL-like lists): when inserting a range
          of forward iterators in a STL-like list, the insertion function can detect
          the number of needed elements and allocate in a single call. The nodes
          still can be deallocated.
        </p>
<p>
          Allocating N buffers of different sizes can be used to speed up allocation
          in cases where several objects must always be allocated at the same time
          but deallocated at different times. For example, a class might perform
          several initial allocations (some header data for a network packet, for
          example) in its constructor but also allocations of buffers that might
          be reallocated in the future (the data to be sent through the network).
          Instead of allocating all the data independently, the constructor might
          use <code class="computeroutput"><span class="identifier">allocate_many</span><span class="special">()</span></code>
          to speed up the initialization, but it still can deallocate and expand
          the memory of the variable size element.
        </p>
<p>
          In general, <code class="computeroutput"><span class="identifier">allocate_many</span></code>
          is useful with large values of N. Overuse of <code class="computeroutput"><span class="identifier">allocate_many</span></code>
          can increase the effective memory usage, because it can't reuse existing
          non-contiguous memory fragments that might be available for some of the
          elements.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_expand_in_place"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_expand_in_place" title="Expand in place memory allocation">Expand
        in place memory allocation</a>
</h4></div></div></div>
<p>
          When programming some data structures such as vectors, memory reallocation
          becomes an important tool to improve performance. Managed memory segments
          offer an advanced reallocation function that offers:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              Forward expansion: An allocated buffer can be expanded so that the
              end of the buffer is moved further. New data can be written between
              the old end and the new end.
            </li>
<li class="listitem">
              Backwards expansion: An allocated buffer can be expanded so that the
              beginning of the buffer is moved backwards. New data can be written
              between the new beginning and the old beginning.
            </li>
<li class="listitem">
              Shrinking: An allocated buffer can be shrunk so that the end of the
              buffer is moved backwards. The memory between the new end and the old
              end can be reused for future allocations.
            </li>
</ul></div>
<p>
          The expansion can be combined with the allocation of a new buffer if the
          expansion fails obtaining a function with "expand, if fails allocate
          a new buffer" semantics.
        </p>
<p>
          Apart from this features, the function always returns the real size of
          the allocated buffer, because many times, due to alignment issues the allocated
          buffer a bit bigger than the requested size. Thus, the programmer can maximize
          the memory use using <code class="computeroutput"><span class="identifier">allocation_command</span></code>.
        </p>
<p>
          Here is the declaration of the function:
        </p>
<pre class="programlisting"><span class="keyword">enum</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocation_type</span>
<span class="special">{</span>
   <span class="comment">//Bitwise OR (|) combinable values</span>
   <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocate_new</span>        <span class="special">=</span> <span class="special">...,</span>
   <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span>          <span class="special">=</span> <span class="special">...,</span>
   <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span>          <span class="special">=</span> <span class="special">...,</span>
   <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">shrink_in_place</span>     <span class="special">=</span> <span class="special">...,</span>
   <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span>  <span class="special">=</span> <span class="special">...</span>
<span class="special">};</span>


<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="identifier">T</span> <span class="special">*,</span> <span class="keyword">bool</span><span class="special">&gt;</span>
   <span class="identifier">allocation_command</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocation_type</span> <span class="identifier">command</span>
                     <span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">limit_size</span>
                     <span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">preferred_size</span>
                     <span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="special">&amp;</span><span class="identifier">received_size</span>
                     <span class="special">,</span> <span class="identifier">T</span> <span class="special">*</span><span class="identifier">reuse_ptr</span> <span class="special">=</span> <span class="number">0</span><span class="special">);</span>
</pre>
<p>
          <span class="bold"><strong>Preconditions for the function</strong></span>:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              If the parameter command contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">shrink_in_place</span></code>
              it can't contain any of these values: <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code>,
              <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code>.
            </li>
<li class="listitem">
              If the parameter command contains <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code>
              or <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code>, the parameter <code class="computeroutput"><span class="identifier">reuse_ptr</span></code> must be non-null and returned
              by a previous allocation function.
            </li>
<li class="listitem">
              If the parameter command contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">shrink_in_place</span></code>,
              the parameter <code class="computeroutput"><span class="identifier">limit_size</span></code>
              must be equal or greater than the parameter <code class="computeroutput"><span class="identifier">preferred_size</span></code>.
            </li>
<li class="listitem">
              If the parameter <code class="computeroutput"><span class="identifier">command</span></code>
              contains any of these values: <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code>
              or <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code>, the parameter <code class="computeroutput"><span class="identifier">limit_size</span></code> must be equal or less
              than the parameter <code class="computeroutput"><span class="identifier">preferred_size</span></code>.
            </li>
</ul></div>
<p>
          <span class="bold"><strong>Which are the effects of this function:</strong></span>
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              If the parameter command contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">shrink_in_place</span></code>,
              the function will try to reduce the size of the memory block referenced
              by pointer <code class="computeroutput"><span class="identifier">reuse_ptr</span></code>
              to the value <code class="computeroutput"><span class="identifier">preferred_size</span></code>
              moving only the end of the block. If it's not possible, it will try
              to reduce the size of the memory block as much as possible as long
              as this results in <code class="computeroutput"><span class="identifier">size</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="special">&lt;=</span> <span class="identifier">limit_size</span></code>. Success is reported only
              if this results in <code class="computeroutput"><span class="identifier">preferred_size</span>
              <span class="special">&lt;=</span> <span class="identifier">size</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span></code> and <code class="computeroutput"><span class="identifier">size</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="special">&lt;=</span> <span class="identifier">limit_size</span></code>.
            </li>
<li class="listitem">
              If the parameter <code class="computeroutput"><span class="identifier">command</span></code>
              only contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code>
              (with optional additional <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>),
              the allocator will try to increase the size of the memory block referenced
              by pointer reuse moving only the end of the block to the value <code class="computeroutput"><span class="identifier">preferred_size</span></code>. If it's not possible,
              it will try to increase the size of the memory block as much as possible
              as long as this results in <code class="computeroutput"><span class="identifier">size</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="special">&gt;=</span> <span class="identifier">limit_size</span></code>. Success is reported only
              if this results in <code class="computeroutput"><span class="identifier">limit_size</span>
              <span class="special">&lt;=</span> <span class="identifier">size</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span></code>.
            </li>
<li class="listitem">
              If the parameter <code class="computeroutput"><span class="identifier">command</span></code>
              only contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code>
              (with optional additional <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>),
              the allocator will try to increase the size of the memory block referenced
              by pointer <code class="computeroutput"><span class="identifier">reuse_ptr</span></code>
              only moving the start of the block to a returned new position <code class="computeroutput"><span class="identifier">new_ptr</span></code>. If it's not possible, it
              will try to move the start of the block as much as possible as long
              as this results in <code class="computeroutput"><span class="identifier">size</span><span class="special">(</span><span class="identifier">new_ptr</span><span class="special">)</span> <span class="special">&gt;=</span> <span class="identifier">limit_size</span></code>. Success is reported only
              if this results in <code class="computeroutput"><span class="identifier">limit_size</span>
              <span class="special">&lt;=</span> <span class="identifier">size</span><span class="special">(</span><span class="identifier">new_ptr</span><span class="special">)</span></code>.
            </li>
<li class="listitem">
              If the parameter <code class="computeroutput"><span class="identifier">command</span></code>
              only contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocate_new</span></code>
              (with optional additional <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>),
              the allocator will try to allocate memory for <code class="computeroutput"><span class="identifier">preferred_size</span></code>
              objects. If it's not possible it will try to allocate memory for at
              least <code class="computeroutput"><span class="identifier">limit_size</span></code> objects.
            </li>
<li class="listitem">
              If the parameter <code class="computeroutput"><span class="identifier">command</span></code>
              only contains a combination of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code>
              and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocate_new</span></code>, (with optional additional
              <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>) the allocator
              will try first the forward expansion. If this fails, it would try a
              new allocation.
            </li>
<li class="listitem">
              If the parameter <code class="computeroutput"><span class="identifier">command</span></code>
              only contains a combination of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code>
              and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocate_new</span></code> (with optional additional
              <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>), the allocator
              will try first to obtain <code class="computeroutput"><span class="identifier">preferred_size</span></code>
              objects using both methods if necessary. If this fails, it will try
              to obtain <code class="computeroutput"><span class="identifier">limit_size</span></code>
              objects using both methods if necessary.
            </li>
<li class="listitem">
              If the parameter <code class="computeroutput"><span class="identifier">command</span></code>
              only contains a combination of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code>
              and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code> (with optional additional
              <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>), the allocator
              will try first forward expansion. If this fails it will try to obtain
              preferred_size objects using backwards expansion or a combination of
              forward and backwards expansion. If this fails, it will try to obtain
              <code class="computeroutput"><span class="identifier">limit_size</span></code> objects
              using both methods if necessary.
            </li>
<li class="listitem">
              If the parameter <code class="computeroutput"><span class="identifier">command</span></code>
              only contains a combination of allocation_new, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code>
              and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code>, (with optional additional
              <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>) the allocator
              will try first forward expansion. If this fails it will try to obtain
              preferred_size objects using new allocation, backwards expansion or
              a combination of forward and backwards expansion. If this fails, it
              will try to obtain <code class="computeroutput"><span class="identifier">limit_size</span></code>
              objects using the same methods.
            </li>
<li class="listitem">
              The allocator always writes the size or the expanded/allocated/shrunk
              memory block in <code class="computeroutput"><span class="identifier">received_size</span></code>.
              On failure the allocator writes in <code class="computeroutput"><span class="identifier">received_size</span></code>
              a possibly successful <code class="computeroutput"><span class="identifier">limit_size</span></code>
              parameter for a new call.
            </li>
</ul></div>
<p>
          <span class="bold"><strong>Throws an exception if two conditions are met:</strong></span>
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              The allocator is unable to allocate/expand/shrink the memory or there
              is an error in preconditions
            </li>
<li class="listitem">
              The parameter command does not contain <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>.
            </li>
</ul></div>
<p>
          <span class="bold"><strong>This function returns:</strong></span>
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              The address of the allocated memory or the new address of the expanded
              memory as the first member of the pair. If the parameter command contains
              <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code> the first member
              will be 0 if the allocation/expansion fails or there is an error in
              preconditions.
            </li>
<li class="listitem">
              The second member of the pair will be false if the memory has been
              allocated, true if the memory has been expanded. If the first member
              is 0, the second member has an undefined value.
            </li>
</ul></div>
<p>
          <span class="bold"><strong>Notes:</strong></span>
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              If the user chooses <code class="computeroutput"><span class="keyword">char</span></code>
              as template argument the returned buffer will be suitably aligned to
              hold any type.
            </li>
<li class="listitem">
              If the user chooses <code class="computeroutput"><span class="keyword">char</span></code>
              as template argument and a backwards expansion is performed, although
              properly aligned, the returned buffer might not be suitable because
              the distance between the new beginning and the old beginning might
              not multiple of the type the user wants to construct, since due to
              internal restrictions the expansion can be slightly bigger than the
              requested bytes. <span class="bold"><strong>When performing backwards expansion,
              if you have already constructed objects in the old buffer, make sure
              to specify correctly the type.</strong></span>
            </li>
</ul></div>
<p>
          Here is a small example that shows the use of <code class="computeroutput"><span class="identifier">allocation_command</span></code>:
        </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>

<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
   <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>

   <span class="comment">//Remove shared memory on construction and destruction</span>
   <span class="keyword">struct</span> <span class="identifier">shm_remove</span>
   <span class="special">{</span>
      <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
      <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span>
   <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span>

   <span class="comment">//Managed memory segment that allocates portions of a shared memory</span>
   <span class="comment">//segment with the default management algorithm</span>
   <span class="identifier">managed_shared_memory</span> <span class="identifier">managed_shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">10000</span><span class="special">*</span><span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">));</span>

   <span class="comment">//Allocate at least 100 bytes, 1000 bytes if possible</span>
   <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">min_size</span> <span class="special">=</span> <span class="number">100</span><span class="special">,</span> <span class="identifier">preferred_size</span> <span class="special">=</span> <span class="number">1000</span><span class="special">;</span>
   <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">received_size</span><span class="special">;</span>
   <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocation_command</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span>
      <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocate_new</span><span class="special">,</span> <span class="identifier">min_size</span><span class="special">,</span> <span class="identifier">preferred_size</span><span class="special">,</span> <span class="identifier">received_size</span><span class="special">).</span><span class="identifier">first</span><span class="special">;</span>

   <span class="comment">//Received size must be bigger than min_size</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">received_size</span> <span class="special">&gt;=</span> <span class="identifier">min_size</span><span class="special">);</span>

   <span class="comment">//Get free memory</span>
   <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">free_memory_after_allocation</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_free_memory</span><span class="special">();</span>

   <span class="comment">//Now write the data</span>
   <span class="keyword">for</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">&lt;</span> <span class="identifier">received_size</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">ptr</span><span class="special">[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>

   <span class="comment">//Now try to triplicate the buffer. We won't admit an expansion</span>
   <span class="comment">//lower to the double of the original buffer.</span>
   <span class="comment">//This "should" be successful since no other class is allocating</span>
   <span class="comment">//memory from the segment</span>
   <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">expanded_size</span><span class="special">;</span>
   <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="special">*,</span> <span class="keyword">bool</span><span class="special">&gt;</span> <span class="identifier">ret</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocation_command</span>
      <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span><span class="special">,</span> <span class="identifier">received_size</span><span class="special">*</span><span class="number">2</span><span class="special">,</span> <span class="identifier">received_size</span><span class="special">*</span><span class="number">3</span><span class="special">,</span> <span class="identifier">expanded_size</span><span class="special">,</span> <span class="identifier">ptr</span><span class="special">);</span>

   <span class="comment">//Check invariants</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">ret</span><span class="special">.</span><span class="identifier">second</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">ret</span><span class="special">.</span><span class="identifier">first</span> <span class="special">==</span> <span class="identifier">ptr</span><span class="special">);</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">expanded_size</span> <span class="special">&gt;=</span> <span class="identifier">received_size</span><span class="special">*</span><span class="number">2</span><span class="special">);</span>

   <span class="comment">//Get free memory and compare</span>
   <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">free_memory_after_expansion</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_free_memory</span><span class="special">();</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">free_memory_after_expansion</span> <span class="special">&lt;</span> <span class="identifier">free_memory_after_allocation</span><span class="special">);</span>

   <span class="comment">//Write new values</span>
   <span class="keyword">for</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">received_size</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">&lt;</span> <span class="identifier">expanded_size</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span>  <span class="identifier">ptr</span><span class="special">[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>

   <span class="comment">//Try to shrink approximately to min_size, but the new size</span>
   <span class="comment">//should be smaller than min_size*2.</span>
   <span class="comment">//This "should" be successful since no other class is allocating</span>
   <span class="comment">//memory from the segment</span>
   <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">shrunk_size</span><span class="special">;</span>
   <span class="identifier">ret</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocation_command</span>
      <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">shrink_in_place</span><span class="special">,</span> <span class="identifier">min_size</span><span class="special">*</span><span class="number">2</span><span class="special">,</span> <span class="identifier">min_size</span><span class="special">,</span> <span class="identifier">shrunk_size</span><span class="special">,</span> <span class="identifier">ptr</span><span class="special">);</span>

   <span class="comment">//Check invariants</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">ret</span><span class="special">.</span><span class="identifier">second</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">ret</span><span class="special">.</span><span class="identifier">first</span> <span class="special">==</span> <span class="identifier">ptr</span><span class="special">);</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">shrunk_size</span> <span class="special">&lt;=</span> <span class="identifier">min_size</span><span class="special">*</span><span class="number">2</span><span class="special">);</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">shrunk_size</span> <span class="special">&gt;=</span> <span class="identifier">min_size</span><span class="special">);</span>

   <span class="comment">//Get free memory and compare</span>
   <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">free_memory_after_shrinking</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_free_memory</span><span class="special">();</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">free_memory_after_shrinking</span> <span class="special">&gt;</span> <span class="identifier">free_memory_after_expansion</span><span class="special">);</span>

   <span class="comment">//Deallocate the buffer</span>
   <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span>
   <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
        </p>
<p>
          <code class="computeroutput"><span class="identifier">allocation_command</span></code> is a
          very powerful function that can lead to important performance gains. It's
          specially useful when programming vector-like data structures where the
          programmer can minimize both the number of allocation requests and the
          memory waste.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.copy_on_write_read_only"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.copy_on_write_read_only" title="Opening managed shared memory and mapped files with Copy On Write or Read Only modes">Opening
        managed shared memory and mapped files with Copy On Write or Read Only modes</a>
</h4></div></div></div>
<p>
          When mapping a memory segment based on shared memory or files, there is
          an option to open them using <span class="bold"><strong>open_copy_on_write</strong></span>
          option. This option is similar to <code class="computeroutput"><span class="identifier">open_only</span></code>
          but every change the programmer does with this managed segment is kept
          private to this process and is not translated to the underlying device
          (shared memory or file).
        </p>
<p>
          The underlying shared memory or file is opened as read-only so several
          processes can share an initial managed segment and make private changes
          to it. If many processes open a managed segment in copy on write mode and
          not modified pages from the managed segment will be shared between all
          those processes, with considerable memory savings.
        </p>
<p>
          Opening managed shared memory and mapped files with <span class="bold"><strong>open_read_only</strong></span>
          maps the underlying device in memory with <span class="bold"><strong>read-only</strong></span>
          attributes. This means that any attempt to write that memory, either creating
          objects or locking any mutex might result in an page-fault error (and thus,
          program termination) from the OS. Read-only mode opens the underlying device
          (shared memory, file...) in read-only mode and can result in considerable
          memory savings if several processes just want to process a managed memory
          segment without modifying it. Read-only mode operations are limited:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              Read-only mode must be used only from managed classes. If the programmer
              obtains the segment manager and tries to use it directly it might result
              in an access violation. The reason for this is that the segment manager
              is placed in the underlying device and does not nothing about the mode
              it's been mapped in memory.
            </li>
<li class="listitem">
              Only const member functions from managed segments should be used.
            </li>
<li class="listitem">
              Additionally, the <code class="computeroutput"><span class="identifier">find</span><span class="special">&lt;&gt;</span></code> member function avoids using
              internal locks and can be used to look for named and unique objects.
            </li>
</ul></div>
<p>
          Here is an example that shows the use of these two open modes:
        </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_mapped_file</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">fstream</span><span class="special">&gt;</span> <span class="comment">//std::fstream</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iterator</span><span class="special">&gt;//</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">distance</span>


<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
   <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>

   <span class="comment">//Define file names</span>
   <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">ManagedFile</span>  <span class="special">=</span> <span class="string">"MyManagedFile"</span><span class="special">;</span>
   <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">ManagedFile2</span> <span class="special">=</span> <span class="string">"MyManagedFile2"</span><span class="special">;</span>

   <span class="comment">//Try to erase any previous managed segment with the same name</span>
   <span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">ManagedFile</span><span class="special">);</span>
   <span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">ManagedFile2</span><span class="special">);</span>
   <span class="identifier">remove_file_on_destroy</span> <span class="identifier">destroyer1</span><span class="special">(</span><span class="identifier">ManagedFile</span><span class="special">);</span>
   <span class="identifier">remove_file_on_destroy</span> <span class="identifier">destroyer2</span><span class="special">(</span><span class="identifier">ManagedFile2</span><span class="special">);</span>

   <span class="special">{</span>
      <span class="comment">//Create an named integer in a managed mapped file</span>
      <span class="identifier">managed_mapped_file</span> <span class="identifier">managed_file</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="identifier">ManagedFile</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span>
      <span class="identifier">managed_file</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="string">"MyInt"</span><span class="special">)(</span><span class="number">0u</span><span class="special">);</span>

      <span class="comment">//Now create a copy on write version</span>
      <span class="identifier">managed_mapped_file</span> <span class="identifier">managed_file_cow</span><span class="special">(</span><span class="identifier">open_copy_on_write</span><span class="special">,</span> <span class="identifier">ManagedFile</span><span class="special">);</span>

      <span class="comment">//Erase the int and create a new one</span>
      <span class="keyword">if</span><span class="special">(!</span><span class="identifier">managed_file_cow</span><span class="special">.</span><span class="identifier">destroy</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="string">"MyInt"</span><span class="special">))</span>
         <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span>
      <span class="identifier">managed_file_cow</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="string">"MyInt2"</span><span class="special">);</span>

      <span class="comment">//Check changes</span>
      <span class="keyword">if</span><span class="special">(</span><span class="identifier">managed_file_cow</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="string">"MyInt"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">&amp;&amp;</span> <span class="special">!</span><span class="identifier">managed_file_cow</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="string">"MyInt2"</span><span class="special">).</span><span class="identifier">first</span><span class="special">)</span>
         <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span>

      <span class="comment">//Check the original is intact</span>
      <span class="keyword">if</span><span class="special">(!</span><span class="identifier">managed_file</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="string">"MyInt"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">&amp;&amp;</span> <span class="identifier">managed_file</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="string">"MyInt2"</span><span class="special">).</span><span class="identifier">first</span><span class="special">)</span>
         <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span>

      <span class="special">{</span>  <span class="comment">//Dump the modified copy on write segment to a file</span>
         <span class="identifier">std</span><span class="special">::</span><span class="identifier">fstream</span> <span class="identifier">file</span><span class="special">(</span><span class="identifier">ManagedFile2</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">out</span> <span class="special">|</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">binary</span><span class="special">);</span>
         <span class="keyword">if</span><span class="special">(!</span><span class="identifier">file</span><span class="special">)</span>
            <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span>
		 <span class="identifier">file</span><span class="special">.</span><span class="identifier">write</span><span class="special">(</span><span class="keyword">static_cast</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*&gt;(</span><span class="identifier">managed_file_cow</span><span class="special">.</span><span class="identifier">get_address</span><span class="special">()),</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">streamsize</span><span class="special">)</span><span class="identifier">managed_file_cow</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">());</span>
      <span class="special">}</span>

      <span class="comment">//Now open the modified file and test changes</span>
      <span class="identifier">managed_mapped_file</span> <span class="identifier">managed_file_cow2</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="identifier">ManagedFile2</span><span class="special">);</span>
      <span class="keyword">if</span><span class="special">(</span><span class="identifier">managed_file_cow2</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="string">"MyInt"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">&amp;&amp;</span> <span class="special">!</span><span class="identifier">managed_file_cow2</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="string">"MyInt2"</span><span class="special">).</span><span class="identifier">first</span><span class="special">)</span>
         <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span>
   <span class="special">}</span>
   <span class="special">{</span>
      <span class="comment">//Now create a read-only version</span>
      <span class="identifier">managed_mapped_file</span> <span class="identifier">managed_file_ro</span><span class="special">(</span><span class="identifier">open_read_only</span><span class="special">,</span> <span class="identifier">ManagedFile</span><span class="special">);</span>

      <span class="comment">//Check the original is intact</span>
      <span class="keyword">if</span><span class="special">(!</span><span class="identifier">managed_file_ro</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="string">"MyInt"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">&amp;&amp;</span> <span class="identifier">managed_file_ro</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;(</span><span class="string">"MyInt2"</span><span class="special">).</span><span class="identifier">first</span><span class="special">)</span>
         <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span>

      <span class="comment">//Check the number of named objects using the iterators</span>
      <span class="keyword">if</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">distance</span><span class="special">(</span><span class="identifier">managed_file_ro</span><span class="special">.</span><span class="identifier">named_begin</span><span class="special">(),</span>  <span class="identifier">managed_file_ro</span><span class="special">.</span><span class="identifier">named_end</span><span class="special">())</span>  <span class="special">!=</span> <span class="number">1</span> <span class="special">&amp;&amp;</span>
         <span class="identifier">std</span><span class="special">::</span><span class="identifier">distance</span><span class="special">(</span><span class="identifier">managed_file_ro</span><span class="special">.</span><span class="identifier">unique_begin</span><span class="special">(),</span> <span class="identifier">managed_file_ro</span><span class="special">.</span><span class="identifier">unique_end</span><span class="special">())</span> <span class="special">!=</span> <span class="number">0</span> <span class="special">)</span>
         <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span>
   <span class="special">}</span>
   <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
        </p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="interprocess.managed_memory_segments.managed_heap_memory_external_buffer"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer" title="Managed Heap Memory And Managed External Buffer">Managed
      Heap Memory And Managed External Buffer</a>
</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_external_buffer">Managed
        External Buffer: Constructing all Boost.Interprocess objects in a user provided
        buffer</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_heap_memory">Managed
        Heap Memory: Boost.Interprocess machinery in heap memory</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_heap_memory_external_buffer_diff">Differences
        between managed memory segments</a></span></dt>
<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.shared_message_queue_ex">Example:
        Serializing a database through the message queue</a></span></dt>
</dl></div>
<p>
        <span class="bold"><strong>Boost.Interprocess</strong></span> offers managed shared
        memory between processes using <code class="computeroutput"><span class="identifier">managed_shared_memory</span></code>
        or <code class="computeroutput"><span class="identifier">managed_mapped_file</span></code>. Two
        processes just map the same the memory mappable resource and read from and
        write to that object.
      </p>
<p>
        Many times, we don't want to use that shared memory approach and we prefer
        to send serialized data through network, local socket or message queues.
        Serialization can be done through <span class="bold"><strong>Boost.Serialization</strong></span>
        or similar library. However, if two processes share the same ABI (application
        binary interface), we could use the same object and container construction
        capabilities of <code class="computeroutput"><span class="identifier">managed_shared_memory</span></code>
        or <code class="computeroutput"><span class="identifier">managed_heap_memory</span></code> to
        build all the information in a single buffer that will be sent, for example,
        though message queues. The receiver would just copy the data to a local buffer,
        and it could read or modify it directly without deserializing the data .
        This approach can be much more efficient that a complex serialization mechanism.
      </p>
<p>
        Applications for <span class="bold"><strong>Boost.Interprocess</strong></span> services
        using non-shared memory buffers:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            Create and use STL compatible containers and allocators, in systems where
            dynamic memory is not recommendable.
          </li>
<li class="listitem">
            Build complex, easily serializable databases in a single buffer:
            <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                  To share data between threads
                </li>
<li class="listitem">
                  To save and load information from/to files.
                </li>
</ul></div>
          </li>
<li class="listitem">
            Duplicate information (containers, allocators, etc...) just copying the
            contents of one buffer to another one.
          </li>
<li class="listitem">
            Send complex information and objects/databases using serial/inter-process/network
            communications.
          </li>
</ul></div>
<p>
        To help with this management, <span class="bold"><strong>Boost.Interprocess</strong></span>
        provides two useful classes, <code class="computeroutput"><span class="identifier">basic_managed_heap_memory</span></code>
        and <code class="computeroutput"><span class="identifier">basic_managed_external_buffer</span></code>:
      </p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_external_buffer"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_external_buffer" title="Managed External Buffer: Constructing all Boost.Interprocess objects in a user provided buffer">Managed
        External Buffer: Constructing all Boost.Interprocess objects in a user provided
        buffer</a>
</h4></div></div></div>
<p>
          Sometimes, the user wants to create simple objects, STL compatible containers,
          STL compatible strings and more, all in a single buffer. This buffer could
          be a big static buffer, a memory-mapped auxiliary device or any other user
          buffer.
        </p>
<p>
          This would allow an easy serialization and we-ll just need to copy the
          buffer to duplicate all the objects created in the original buffer, including
          complex objects like maps, lists.... <span class="bold"><strong>Boost.Interprocess</strong></span>
          offers managed memory segment classes to handle user provided buffers that
          allow the same functionality as shared memory classes:
        </p>
<pre class="programlisting"><span class="comment">//Named object creation managed memory segment</span>
<span class="comment">//All objects are constructed in a user provided buffer</span>
<span class="keyword">template</span> <span class="special">&lt;</span>
            <span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span>
            <span class="keyword">class</span> <span class="identifier">MemoryAlgorithm</span><span class="special">,</span>
            <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">IndexConfig</span><span class="special">&gt;</span> <span class="keyword">class</span> <span class="identifier">IndexType</span>
         <span class="special">&gt;</span>
<span class="keyword">class</span> <span class="identifier">basic_managed_external_buffer</span><span class="special">;</span>

<span class="comment">//Named object creation managed memory segment</span>
<span class="comment">//All objects are constructed in a user provided buffer</span>
<span class="comment">//   Names are c-strings,</span>
<span class="comment">//   Default memory management algorithm</span>
<span class="comment">//    (rbtree_best_fit with no mutexes and relative pointers)</span>
<span class="comment">//   Name-object mappings are stored in the default index type (flat_map)</span>
<span class="keyword">typedef</span> <span class="identifier">basic_managed_external_buffer</span> <span class="special">&lt;</span>
   <span class="keyword">char</span><span class="special">,</span>
   <span class="identifier">rbtree_best_fit</span><span class="special">&lt;</span><span class="identifier">null_mutex_family</span><span class="special">,</span> <span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="special">&gt;,</span>
   <span class="identifier">flat_map_index</span>
   <span class="special">&gt;</span>  <span class="identifier">managed_external_buffer</span><span class="special">;</span>

<span class="comment">//Named object creation managed memory segment</span>
<span class="comment">//All objects are constructed in a user provided buffer</span>
<span class="comment">//   Names are wide-strings,</span>
<span class="comment">//   Default memory management algorithm</span>
<span class="comment">//    (rbtree_best_fit with no mutexes and relative pointers)</span>
<span class="comment">//   Name-object mappings are stored in the default index type (flat_map)</span>
<span class="keyword">typedef</span> <span class="identifier">basic_managed_external_buffer</span><span class="special">&lt;</span>
   <span class="keyword">wchar_t</span><span class="special">,</span>
   <span class="identifier">rbtree_best_fit</span><span class="special">&lt;</span><span class="identifier">null_mutex_family</span><span class="special">,</span> <span class="identifier">offset_ptr</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="special">&gt;,</span>
   <span class="identifier">flat_map_index</span>
   <span class="special">&gt;</span>  <span class="identifier">wmanaged_external_buffer</span><span class="special">;</span>
</pre>
<p>
          To use a managed external buffer, you must include the following header:
        </p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_external_buffer</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
          Let's see an example of the use of managed_external_buffer:
        </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_external_buffer</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cstring</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">aligned_storage</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>

<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
   <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>

   <span class="comment">//Create the static memory who will store all objects</span>
   <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">memsize</span> <span class="special">=</span> <span class="number">65536</span><span class="special">;</span>

   <span class="keyword">static</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">aligned_storage</span><span class="special">&lt;</span><span class="identifier">memsize</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">static_buffer</span><span class="special">;</span>

   <span class="comment">//This managed memory will construct objects associated with</span>
   <span class="comment">//a wide string in the static buffer</span>
   <span class="identifier">wmanaged_external_buffer</span> <span class="identifier">objects_in_static_memory</span>
      <span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">static_buffer</span><span class="special">,</span> <span class="identifier">memsize</span><span class="special">);</span>

   <span class="comment">//We optimize resources to create 100 named objects in the static buffer</span>
   <span class="identifier">objects_in_static_memory</span><span class="special">.</span><span class="identifier">reserve_named_objects</span><span class="special">(</span><span class="number">100</span><span class="special">);</span>

   <span class="comment">//Alias an integer node allocator type</span>
   <span class="comment">//This allocator will allocate memory inside the static buffer</span>
   <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">wmanaged_external_buffer</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
      <span class="identifier">allocator_t</span><span class="special">;</span>

   <span class="comment">//Alias a STL compatible list to be constructed in the static buffer</span>
   <span class="keyword">typedef</span> <span class="identifier">list</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">allocator_t</span><span class="special">&gt;</span>    <span class="identifier">MyBufferList</span><span class="special">;</span>

   <span class="comment">//The list must be initialized with the allocator</span>
   <span class="comment">//All objects created with objects_in_static_memory will</span>
   <span class="comment">//be stored in the static_buffer!</span>
   <span class="identifier">MyBufferList</span> <span class="special">*</span><span class="identifier">list</span> <span class="special">=</span> <span class="identifier">objects_in_static_memory</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyBufferList</span><span class="special">&gt;(</span><span class="identifier">L</span><span class="string">"MyList"</span><span class="special">)</span>
                           <span class="special">(</span><span class="identifier">objects_in_static_memory</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
   <span class="comment">//Since the allocation algorithm from wmanaged_external_buffer uses relative</span>
   <span class="comment">//pointers and all the pointers constructed int the static memory point</span>
   <span class="comment">//to objects in the same segment,  we can create another static buffer</span>
   <span class="comment">//from the first one and duplicate all the data.</span>
   <span class="keyword">static</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">aligned_storage</span><span class="special">&lt;</span><span class="identifier">memsize</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">static_buffer2</span><span class="special">;</span>
   <span class="identifier">std</span><span class="special">::</span><span class="identifier">memcpy</span><span class="special">(&amp;</span><span class="identifier">static_buffer2</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">static_buffer</span><span class="special">,</span> <span class="identifier">memsize</span><span class="special">);</span>

   <span class="comment">//Now open the duplicated managed memory passing the memory as argument</span>
   <span class="identifier">wmanaged_external_buffer</span> <span class="identifier">objects_in_static_memory2</span>
      <span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">static_buffer2</span><span class="special">,</span> <span class="identifier">memsize</span><span class="special">);</span>

   <span class="comment">//Check that "MyList" has been duplicated in the second buffer</span>
   <span class="keyword">if</span><span class="special">(!</span><span class="identifier">objects_in_static_memory2</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">MyBufferList</span><span class="special">&gt;(</span><span class="identifier">L</span><span class="string">"MyList"</span><span class="special">).</span><span class="identifier">first</span><span class="special">)</span>
      <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>

   <span class="comment">//Destroy the lists from the static buffers</span>
   <span class="identifier">objects_in_static_memory</span><span class="special">.</span><span class="identifier">destroy</span><span class="special">&lt;</span><span class="identifier">MyBufferList</span><span class="special">&gt;(</span><span class="identifier">L</span><span class="string">"MyList"</span><span class="special">);</span>
   <span class="identifier">objects_in_static_memory2</span><span class="special">.</span><span class="identifier">destroy</span><span class="special">&lt;</span><span class="identifier">MyBufferList</span><span class="special">&gt;(</span><span class="identifier">L</span><span class="string">"MyList"</span><span class="special">);</span>
   <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
        </p>
<p>
          <span class="bold"><strong>Boost.Interprocess</strong></span> STL compatible allocators
          can also be used to place STL compatible containers in the user segment.
        </p>
<p>
          <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_managed__idp27919256.html" title="Class template basic_managed_external_buffer">basic_managed_external_buffer</a></code>
          can be also useful to build small databases for embedded systems limiting
          the size of the used memory to a predefined memory chunk, instead of letting
          the database fragment the heap memory.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_heap_memory"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_heap_memory" title="Managed Heap Memory: Boost.Interprocess machinery in heap memory">Managed
        Heap Memory: Boost.Interprocess machinery in heap memory</a>
</h4></div></div></div>
<p>
          The use of heap memory (new/delete) to obtain a buffer where the user wants
          to store all his data is very common, so <span class="bold"><strong>Boost.Interprocess</strong></span>
          provides some specialized classes that work exclusively with heap memory.
        </p>
<p>
          These are the classes:
        </p>
<pre class="programlisting"><span class="comment">//Named object creation managed memory segment</span>
<span class="comment">//All objects are constructed in a single buffer allocated via new[]</span>
<span class="keyword">template</span> <span class="special">&lt;</span>
            <span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span>
            <span class="keyword">class</span> <span class="identifier">MemoryAlgorithm</span><span class="special">,</span>
            <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">IndexConfig</span><span class="special">&gt;</span> <span class="keyword">class</span> <span class="identifier">IndexType</span>
         <span class="special">&gt;</span>
<span class="keyword">class</span> <span class="identifier">basic_managed_heap_memory</span><span class="special">;</span>

<span class="comment">//Named object creation managed memory segment</span>
<span class="comment">//All objects are constructed in a single buffer allocated via new[]</span>
<span class="comment">//   Names are c-strings,</span>
<span class="comment">//   Default memory management algorithm</span>
<span class="comment">//    (rbtree_best_fit with no mutexes and relative pointers)</span>
<span class="comment">//   Name-object mappings are stored in the default index type (flat_map)</span>
<span class="keyword">typedef</span> <span class="identifier">basic_managed_heap_memory</span> <span class="special">&lt;</span>
   <span class="keyword">char</span><span class="special">,</span>
   <span class="identifier">rbtree_best_fit</span><span class="special">&lt;</span><span class="identifier">null_mutex_family</span><span class="special">&gt;,</span>
   <span class="identifier">flat_map_index</span>
   <span class="special">&gt;</span>  <span class="identifier">managed_heap_memory</span><span class="special">;</span>

<span class="comment">//Named object creation managed memory segment</span>
<span class="comment">//All objects are constructed in a single buffer allocated via new[]</span>
<span class="comment">//   Names are wide-strings,</span>
<span class="comment">//   Default memory management algorithm</span>
<span class="comment">//    (rbtree_best_fit with no mutexes and relative pointers)</span>
<span class="comment">//   Name-object mappings are stored in the default index type (flat_map)</span>
<span class="keyword">typedef</span> <span class="identifier">basic_managed_heap_memory</span><span class="special">&lt;</span>
   <span class="keyword">wchar_t</span><span class="special">,</span>
   <span class="identifier">rbtree_best_fit</span><span class="special">&lt;</span><span class="identifier">null_mutex_family</span><span class="special">&gt;,</span>
   <span class="identifier">flat_map_index</span>
   <span class="special">&gt;</span>  <span class="identifier">wmanaged_heap_memory</span><span class="special">;</span>
</pre>
<p>
          To use a managed heap memory, you must include the following header:
        </p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_heap_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
          The use is exactly the same as <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_managed__idp27919256.html" title="Class template basic_managed_external_buffer">basic_managed_external_buffer</a></code>,
          except that memory is created by the managed memory segment itself using
          dynamic (new/delete) memory.
        </p>
<p>
          <span class="bold"><strong>basic_managed_heap_memory</strong></span> also offers
          a <code class="computeroutput"><span class="identifier">grow</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">extra_bytes</span><span class="special">)</span></code> function that tries to resize internal
          heap memory so that we have room for more objects. But <span class="bold"><strong>be
          careful</strong></span>, if memory is reallocated, the old buffer will be copied
          into the new one so all the objects will be binary-copied to the new buffer.
          To be able to use this function, all pointers constructed in the heap buffer
          that point to objects in the heap buffer must be relative pointers (for
          example <code class="computeroutput"><span class="identifier">offset_ptr</span></code>). Otherwise,
          the result is undefined. Here is an example:
        </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_heap_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cstddef</span><span class="special">&gt;</span>

<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">list</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">allocator</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_heap_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span> <span class="special">&gt;</span>
   <span class="identifier">MyList</span><span class="special">;</span>

<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
<span class="special">{</span>
   <span class="comment">//We will create a buffer of 1000 bytes to store a list</span>
   <span class="identifier">managed_heap_memory</span> <span class="identifier">heap_memory</span><span class="special">(</span><span class="number">1000</span><span class="special">);</span>

   <span class="identifier">MyList</span> <span class="special">*</span> <span class="identifier">mylist</span> <span class="special">=</span> <span class="identifier">heap_memory</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyList</span><span class="special">&gt;(</span><span class="string">"MyList"</span><span class="special">)</span>
                        <span class="special">(</span><span class="identifier">heap_memory</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>

   <span class="comment">//Obtain handle, that identifies the list in the buffer</span>
   <span class="identifier">managed_heap_memory</span><span class="special">::</span><span class="identifier">handle_t</span> <span class="identifier">list_handle</span> <span class="special">=</span> <span class="identifier">heap_memory</span><span class="special">.</span><span class="identifier">get_handle_from_address</span><span class="special">(</span><span class="identifier">mylist</span><span class="special">);</span>

   <span class="comment">//Fill list until there is no more memory in the buffer</span>
   <span class="keyword">try</span><span class="special">{</span>
      <span class="keyword">while</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special">{</span>
         <span class="identifier">mylist</span><span class="special">-&gt;</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">mylist</span><span class="special">-&gt;</span><span class="identifier">begin</span><span class="special">(),</span> <span class="number">0</span><span class="special">);</span>
      <span class="special">}</span>
   <span class="special">}</span>
   <span class="keyword">catch</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bad_alloc</span> <span class="special">&amp;){</span>
      <span class="comment">//memory is full</span>
   <span class="special">}</span>
   <span class="comment">//Let's obtain the size of the list</span>
   <span class="identifier">MyList</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">old_size</span> <span class="special">=</span> <span class="identifier">mylist</span><span class="special">-&gt;</span><span class="identifier">size</span><span class="special">();</span>

   <span class="comment">//To make the list bigger, let's increase the heap buffer</span>
   <span class="comment">//in 1000 bytes more.</span>
   <span class="identifier">heap_memory</span><span class="special">.</span><span class="identifier">grow</span><span class="special">(</span><span class="number">1000</span><span class="special">);</span>

   <span class="comment">//If memory has been reallocated, the old pointer is invalid, so</span>
   <span class="comment">//use previously obtained handle to find the new pointer.</span>
   <span class="identifier">mylist</span> <span class="special">=</span> <span class="keyword">static_cast</span><span class="special">&lt;</span><span class="identifier">MyList</span> <span class="special">*&gt;</span>
               <span class="special">(</span><span class="identifier">heap_memory</span><span class="special">.</span><span class="identifier">get_address_from_handle</span><span class="special">(</span><span class="identifier">list_handle</span><span class="special">));</span>

   <span class="comment">//Fill list until there is no more memory in the buffer</span>
   <span class="keyword">try</span><span class="special">{</span>
      <span class="keyword">while</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special">{</span>
         <span class="identifier">mylist</span><span class="special">-&gt;</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">mylist</span><span class="special">-&gt;</span><span class="identifier">begin</span><span class="special">(),</span> <span class="number">0</span><span class="special">);</span>
      <span class="special">}</span>
   <span class="special">}</span>
   <span class="keyword">catch</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bad_alloc</span> <span class="special">&amp;){</span>
      <span class="comment">//memory is full</span>
   <span class="special">}</span>

   <span class="comment">//Let's obtain the new size of the list</span>
   <span class="identifier">MyList</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">new_size</span> <span class="special">=</span> <span class="identifier">mylist</span><span class="special">-&gt;</span><span class="identifier">size</span><span class="special">();</span>

   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">new_size</span> <span class="special">&gt;</span> <span class="identifier">old_size</span><span class="special">);</span>

   <span class="comment">//Destroy list</span>
   <span class="identifier">heap_memory</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">mylist</span><span class="special">);</span>

   <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_heap_memory_external_buffer_diff"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_heap_memory_external_buffer_diff" title="Differences between managed memory segments">Differences
        between managed memory segments</a>
</h4></div></div></div>
<p>
          All managed memory segments have similar capabilities (memory allocation
          inside the memory segment, named object construction...), but there are
          some remarkable differences between <span class="bold"><strong>managed_shared_memory</strong></span>,
          <span class="bold"><strong>managed_mapped_file</strong></span> and <span class="bold"><strong>managed_heap_memory</strong></span>,
          <span class="bold"><strong>managed_external_file</strong></span>.
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              Default specializations of managed shared memory and mapped file use
              process-shared mutexes. Heap memory and external buffer have no internal
              synchronization by default. The cause is that the first two are thought
              to be shared between processes (although memory mapped files could
              be used just to obtain a persistent object data-base for a process)
              whereas the last two are thought to be used inside one process to construct
              a serialized named object data-base that can be sent though serial
              interprocess communications (like message queues, localhost network...).
            </li>
<li class="listitem">
              The first two create a system-global object (a shared memory object
              or a file) shared by several processes, whereas the last two are objects
              that don't create system-wide resources.
            </li>
</ul></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interprocess.managed_memory_segments.managed_heap_memory_external_buffer.shared_message_queue_ex"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.shared_message_queue_ex" title="Example: Serializing a database through the message queue">Example:
        Serializing a database through the message queue</a>
</h4></div></div></div>
<p>
          To see the utility of managed heap memory and managed external buffer classes,
          the following example shows how a message queue can be used to serialize
          a whole database constructed in a memory buffer using <span class="bold"><strong>Boost.Interprocess</strong></span>,
          send the database through a message queue and duplicated in another buffer:
        </p>
<p>
</p>
<pre class="programlisting"><span class="comment">//This test creates a in memory data-base using Interprocess machinery and</span>
<span class="comment">//serializes it through a message queue. Then rebuilds the data-base in</span>
<span class="comment">//another buffer and checks it against the original data-base</span>
<span class="keyword">bool</span> <span class="identifier">test_serialize_db</span><span class="special">()</span>
<span class="special">{</span>
   <span class="comment">//Typedef data to create a Interprocess map</span>
   <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span> <span class="identifier">MyPair</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">less</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span>   <span class="identifier">MyLess</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="identifier">node_allocator</span><span class="special">&lt;</span><span class="identifier">MyPair</span><span class="special">,</span> <span class="identifier">managed_external_buffer</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">&gt;</span>
      <span class="identifier">node_allocator_t</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="identifier">map</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">,</span>
               <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">,</span>
               <span class="identifier">std</span><span class="special">::</span><span class="identifier">less</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;,</span>
               <span class="identifier">node_allocator_t</span><span class="special">&gt;</span>
               <span class="identifier">MyMap</span><span class="special">;</span>

   <span class="comment">//Some constants</span>
   <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">BufferSize</span>  <span class="special">=</span> <span class="number">65536</span><span class="special">;</span>
   <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">MaxMsgSize</span>  <span class="special">=</span> <span class="number">100</span><span class="special">;</span>

   <span class="comment">//Allocate a memory buffer to hold the destiny database using vector&lt;char&gt;</span>
   <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;</span> <span class="identifier">buffer_destiny</span><span class="special">(</span><span class="identifier">BufferSize</span><span class="special">,</span> <span class="number">0</span><span class="special">);</span>

   <span class="identifier">message_queue</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">test</span><span class="special">::</span><span class="identifier">get_process_id_name</span><span class="special">());</span>
   <span class="special">{</span>
      <span class="comment">//Create the message-queues</span>
      <span class="identifier">message_queue</span> <span class="identifier">mq1</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="identifier">test</span><span class="special">::</span><span class="identifier">get_process_id_name</span><span class="special">(),</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">MaxMsgSize</span><span class="special">);</span>

      <span class="comment">//Open previously created message-queue simulating other process</span>
      <span class="identifier">message_queue</span> <span class="identifier">mq2</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="identifier">test</span><span class="special">::</span><span class="identifier">get_process_id_name</span><span class="special">());</span>

      <span class="comment">//A managed heap memory to create the origin database</span>
      <span class="identifier">managed_heap_memory</span> <span class="identifier">db_origin</span><span class="special">(</span><span class="identifier">buffer_destiny</span><span class="special">.</span><span class="identifier">size</span><span class="special">());</span>

      <span class="comment">//Construct the map in the first buffer</span>
      <span class="identifier">MyMap</span> <span class="special">*</span><span class="identifier">map1</span> <span class="special">=</span> <span class="identifier">db_origin</span><span class="special">.</span><span class="identifier">construct</span><span class="special">&lt;</span><span class="identifier">MyMap</span><span class="special">&gt;(</span><span class="string">"MyMap"</span><span class="special">)</span>
                                       <span class="special">(</span><span class="identifier">MyLess</span><span class="special">(),</span>
                                       <span class="identifier">db_origin</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span>
      <span class="keyword">if</span><span class="special">(!</span><span class="identifier">map1</span><span class="special">)</span>
         <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span>

      <span class="comment">//Fill map1 until is full</span>
      <span class="keyword">try</span><span class="special">{</span>
         <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
         <span class="keyword">while</span><span class="special">(</span><span class="number">1</span><span class="special">){</span>
            <span class="special">(*</span><span class="identifier">map1</span><span class="special">)[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>
            <span class="special">++</span><span class="identifier">i</span><span class="special">;</span>
         <span class="special">}</span>
      <span class="special">}</span>
      <span class="keyword">catch</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">bad_alloc</span> <span class="special">&amp;){}</span>

      <span class="comment">//Data control data sending through the message queue</span>
      <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">sent</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
      <span class="identifier">message_queue</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">recvd</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
      <span class="identifier">message_queue</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">total_recvd</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
      <span class="keyword">unsigned</span> <span class="keyword">int</span> <span class="identifier">priority</span><span class="special">;</span>

      <span class="comment">//Send whole first buffer through the mq1, read it</span>
      <span class="comment">//through mq2 to the second buffer</span>
      <span class="keyword">while</span><span class="special">(</span><span class="number">1</span><span class="special">){</span>
         <span class="comment">//Send a fragment of buffer1 through mq1</span>
		 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_to_send</span> <span class="special">=</span> <span class="identifier">MaxMsgSize</span> <span class="special">&lt;</span> <span class="special">(</span><span class="identifier">db_origin</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">()</span> <span class="special">-</span> <span class="identifier">sent</span><span class="special">)</span> <span class="special">?</span>
                                       <span class="identifier">MaxMsgSize</span> <span class="special">:</span> <span class="special">(</span><span class="identifier">db_origin</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">()</span> <span class="special">-</span> <span class="identifier">sent</span><span class="special">);</span>
         <span class="identifier">mq1</span><span class="special">.</span><span class="identifier">send</span><span class="special">(</span> <span class="special">&amp;</span><span class="keyword">static_cast</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">*&gt;(</span><span class="identifier">db_origin</span><span class="special">.</span><span class="identifier">get_address</span><span class="special">())[</span><span class="identifier">sent</span><span class="special">]</span>
               <span class="special">,</span> <span class="identifier">bytes_to_send</span>
               <span class="special">,</span> <span class="number">0</span><span class="special">);</span>
         <span class="identifier">sent</span> <span class="special">+=</span> <span class="identifier">bytes_to_send</span><span class="special">;</span>
         <span class="comment">//Receive the fragment through mq2 to buffer_destiny</span>
		 <span class="identifier">mq2</span><span class="special">.</span><span class="identifier">receive</span><span class="special">(</span> <span class="special">&amp;</span><span class="identifier">buffer_destiny</span><span class="special">[</span><span class="identifier">total_recvd</span><span class="special">]</span>
		          <span class="special">,</span> <span class="identifier">BufferSize</span> <span class="special">-</span> <span class="identifier">recvd</span>
                  <span class="special">,</span> <span class="identifier">recvd</span>
                  <span class="special">,</span> <span class="identifier">priority</span><span class="special">);</span>
         <span class="identifier">total_recvd</span> <span class="special">+=</span> <span class="identifier">recvd</span><span class="special">;</span>

         <span class="comment">//Check if we have received all the buffer</span>
         <span class="keyword">if</span><span class="special">(</span><span class="identifier">total_recvd</span> <span class="special">==</span> <span class="identifier">BufferSize</span><span class="special">){</span>
            <span class="keyword">break</span><span class="special">;</span>
         <span class="special">}</span>
      <span class="special">}</span>

      <span class="comment">//The buffer will contain a copy of the original database</span>
      <span class="comment">//so let's interpret the buffer with managed_external_buffer</span>
      <span class="identifier">managed_external_buffer</span> <span class="identifier">db_destiny</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">buffer_destiny</span><span class="special">[</span><span class="number">0</span><span class="special">],</span> <span class="identifier">BufferSize</span><span class="special">);</span>

      <span class="comment">//Let's find the map</span>
      <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="identifier">MyMap</span> <span class="special">*,</span> <span class="identifier">managed_external_buffer</span><span class="special">::</span><span class="identifier">size_type</span><span class="special">&gt;</span> <span class="identifier">ret</span> <span class="special">=</span> <span class="identifier">db_destiny</span><span class="special">.</span><span class="identifier">find</span><span class="special">&lt;</span><span class="identifier">MyMap</span><span class="special">&gt;(</span><span class="string">"MyMap"</span><span class="special">);</span>
      <span class="identifier">MyMap</span> <span class="special">*</span><span class="identifier">map2</span> <span class="special">=</span> <span class="identifier">ret</span><span class="special">.</span><span class="identifier">first</span><span class="special">;</span>

      <span class="comment">//Check if we have found it</span>
      <span class="keyword">if</span><span class="special">(!</span><span class="identifier">map2</span><span class="special">){</span>
         <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span>
      <span class="special">}</span>

      <span class="comment">//Check if it is a single variable (not an array)</span>
      <span class="keyword">if</span><span class="special">(</span><span class="identifier">ret</span><span class="special">.</span><span class="identifier">second</span> <span class="special">!=</span> <span class="number">1</span><span class="special">){</span>
         <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span>
      <span class="special">}</span>

      <span class="comment">//Now let's compare size</span>
      <span class="keyword">if</span><span class="special">(</span><span class="identifier">map1</span><span class="special">-&gt;</span><span class="identifier">size</span><span class="special">()</span> <span class="special">!=</span> <span class="identifier">map2</span><span class="special">-&gt;</span><span class="identifier">size</span><span class="special">()){</span>
         <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span>
      <span class="special">}</span>

      <span class="comment">//Now let's compare all db values</span>
	  <span class="identifier">MyMap</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">num_elements</span> <span class="special">=</span> <span class="identifier">map1</span><span class="special">-&gt;</span><span class="identifier">size</span><span class="special">();</span>
	  <span class="keyword">for</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">&lt;</span> <span class="identifier">num_elements</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span>
         <span class="keyword">if</span><span class="special">((*</span><span class="identifier">map1</span><span class="special">)[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">!=</span> <span class="special">(*</span><span class="identifier">map2</span><span class="special">)[</span><span class="identifier">i</span><span class="special">]){</span>
            <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span>
         <span class="special">}</span>
      <span class="special">}</span>

      <span class="comment">//Destroy maps from db-s</span>
      <span class="identifier">db_origin</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">map1</span><span class="special">);</span>
      <span class="identifier">db_destiny</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">map2</span><span class="special">);</span>
   <span class="special">}</span>
   <span class="identifier">message_queue</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">test</span><span class="special">::</span><span class="identifier">get_process_id_name</span><span class="special">());</span>
   <span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
        </p>
</div>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright &#169; 2005-2012 Ion Gaztanaga<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="synchronization_mechanisms.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../interprocess.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="allocators_containers.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>