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
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<link rel="stylesheet" href="style.css" type="text/css">
<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="Start" href="index.html">
<link rel="previous" href="Intro.html">
<link rel="next" href="Foreword.html">
<link rel="Up" href="index.html">
<link title="Index of types" rel=Appendix href="index_types.html">
<link title="Index of extensions" rel=Appendix href="index_extensions.html">
<link title="Index of exceptions" rel=Appendix href="index_exceptions.html">
<link title="Index of values" rel=Appendix href="index_values.html">
<link title="Index of class attributes" rel=Appendix href="index_attributes.html">
<link title="Index of class methods" rel=Appendix href="index_methods.html">
<link title="Index of classes" rel=Appendix href="index_classes.html">
<link title="Index of class types" rel=Appendix href="index_class_types.html">
<link title="Index of modules" rel=Appendix href="index_modules.html">
<link title="Index of module types" rel=Appendix href="index_module_types.html">
<link title="Uq_gtk" rel="Chapter" href="Uq_gtk.html">
<link title="Uq_tcl" rel="Chapter" href="Uq_tcl.html">
<link title="Equeue" rel="Chapter" href="Equeue.html">
<link title="Unixqueue" rel="Chapter" href="Unixqueue.html">
<link title="Unixqueue_pollset" rel="Chapter" href="Unixqueue_pollset.html">
<link title="Unixqueue_select" rel="Chapter" href="Unixqueue_select.html">
<link title="Uq_resolver" rel="Chapter" href="Uq_resolver.html">
<link title="Uq_engines" rel="Chapter" href="Uq_engines.html">
<link title="Uq_multiplex" rel="Chapter" href="Uq_multiplex.html">
<link title="Uq_transfer" rel="Chapter" href="Uq_transfer.html">
<link title="Uq_socks5" rel="Chapter" href="Uq_socks5.html">
<link title="Uq_io" rel="Chapter" href="Uq_io.html">
<link title="Uq_lwt" rel="Chapter" href="Uq_lwt.html">
<link title="Uq_libevent" rel="Chapter" href="Uq_libevent.html">
<link title="Uq_mt" rel="Chapter" href="Uq_mt.html">
<link title="Uq_client" rel="Chapter" href="Uq_client.html">
<link title="Uq_server" rel="Chapter" href="Uq_server.html">
<link title="Uq_datagram" rel="Chapter" href="Uq_datagram.html">
<link title="Uq_engines_compat" rel="Chapter" href="Uq_engines_compat.html">
<link title="Equeue_intro" rel="Chapter" href="Equeue_intro.html">
<link title="Equeue_howto" rel="Chapter" href="Equeue_howto.html">
<link title="Netcamlbox" rel="Chapter" href="Netcamlbox.html">
<link title="Netcgi_apache" rel="Chapter" href="Netcgi_apache.html">
<link title="Netcgi_modtpl" rel="Chapter" href="Netcgi_modtpl.html">
<link title="Netcgi_plex" rel="Chapter" href="Netcgi_plex.html">
<link title="Netcgi_common" rel="Chapter" href="Netcgi_common.html">
<link title="Netcgi" rel="Chapter" href="Netcgi.html">
<link title="Netcgi_ajp" rel="Chapter" href="Netcgi_ajp.html">
<link title="Netcgi_scgi" rel="Chapter" href="Netcgi_scgi.html">
<link title="Netcgi_cgi" rel="Chapter" href="Netcgi_cgi.html">
<link title="Netcgi_fcgi" rel="Chapter" href="Netcgi_fcgi.html">
<link title="Netcgi_dbi" rel="Chapter" href="Netcgi_dbi.html">
<link title="Netcgi1_compat" rel="Chapter" href="Netcgi1_compat.html">
<link title="Netcgi_test" rel="Chapter" href="Netcgi_test.html">
<link title="Netcgi_porting" rel="Chapter" href="Netcgi_porting.html">
<link title="Nethttp_client_conncache" rel="Chapter" href="Nethttp_client_conncache.html">
<link title="Nethttp_client" rel="Chapter" href="Nethttp_client.html">
<link title="Nettelnet_client" rel="Chapter" href="Nettelnet_client.html">
<link title="Netftp_data_endpoint" rel="Chapter" href="Netftp_data_endpoint.html">
<link title="Netftp_client" rel="Chapter" href="Netftp_client.html">
<link title="Nethttp_fs" rel="Chapter" href="Nethttp_fs.html">
<link title="Netftp_fs" rel="Chapter" href="Netftp_fs.html">
<link title="Netsmtp" rel="Chapter" href="Netsmtp.html">
<link title="Netpop" rel="Chapter" href="Netpop.html">
<link title="Netldap" rel="Chapter" href="Netldap.html">
<link title="Netclient_tut" rel="Chapter" href="Netclient_tut.html">
<link title="Netgss_bindings" rel="Chapter" href="Netgss_bindings.html">
<link title="Netgss" rel="Chapter" href="Netgss.html">
<link title="Nethttpd_types" rel="Chapter" href="Nethttpd_types.html">
<link title="Nethttpd_kernel" rel="Chapter" href="Nethttpd_kernel.html">
<link title="Nethttpd_reactor" rel="Chapter" href="Nethttpd_reactor.html">
<link title="Nethttpd_engine" rel="Chapter" href="Nethttpd_engine.html">
<link title="Nethttpd_services" rel="Chapter" href="Nethttpd_services.html">
<link title="Nethttpd_plex" rel="Chapter" href="Nethttpd_plex.html">
<link title="Nethttpd_util" rel="Chapter" href="Nethttpd_util.html">
<link title="Nethttpd_intro" rel="Chapter" href="Nethttpd_intro.html">
<link title="Netmcore" rel="Chapter" href="Netmcore.html">
<link title="Netmcore_camlbox" rel="Chapter" href="Netmcore_camlbox.html">
<link title="Netmcore_mempool" rel="Chapter" href="Netmcore_mempool.html">
<link title="Netmcore_heap" rel="Chapter" href="Netmcore_heap.html">
<link title="Netmcore_ref" rel="Chapter" href="Netmcore_ref.html">
<link title="Netmcore_array" rel="Chapter" href="Netmcore_array.html">
<link title="Netmcore_sem" rel="Chapter" href="Netmcore_sem.html">
<link title="Netmcore_mutex" rel="Chapter" href="Netmcore_mutex.html">
<link title="Netmcore_condition" rel="Chapter" href="Netmcore_condition.html">
<link title="Netmcore_queue" rel="Chapter" href="Netmcore_queue.html">
<link title="Netmcore_buffer" rel="Chapter" href="Netmcore_buffer.html">
<link title="Netmcore_matrix" rel="Chapter" href="Netmcore_matrix.html">
<link title="Netmcore_hashtbl" rel="Chapter" href="Netmcore_hashtbl.html">
<link title="Netmcore_process" rel="Chapter" href="Netmcore_process.html">
<link title="Netmcore_tut" rel="Chapter" href="Netmcore_tut.html">
<link title="Netmcore_basics" rel="Chapter" href="Netmcore_basics.html">
<link title="Netplex_types" rel="Chapter" href="Netplex_types.html">
<link title="Netplex_mp" rel="Chapter" href="Netplex_mp.html">
<link title="Netplex_mt" rel="Chapter" href="Netplex_mt.html">
<link title="Netplex_log" rel="Chapter" href="Netplex_log.html">
<link title="Netplex_controller" rel="Chapter" href="Netplex_controller.html">
<link title="Netplex_container" rel="Chapter" href="Netplex_container.html">
<link title="Netplex_sockserv" rel="Chapter" href="Netplex_sockserv.html">
<link title="Netplex_workload" rel="Chapter" href="Netplex_workload.html">
<link title="Netplex_main" rel="Chapter" href="Netplex_main.html">
<link title="Netplex_config" rel="Chapter" href="Netplex_config.html">
<link title="Netplex_kit" rel="Chapter" href="Netplex_kit.html">
<link title="Rpc_netplex" rel="Chapter" href="Rpc_netplex.html">
<link title="Netplex_cenv" rel="Chapter" href="Netplex_cenv.html">
<link title="Netplex_semaphore" rel="Chapter" href="Netplex_semaphore.html">
<link title="Netplex_sharedvar" rel="Chapter" href="Netplex_sharedvar.html">
<link title="Netplex_mutex" rel="Chapter" href="Netplex_mutex.html">
<link title="Netplex_encap" rel="Chapter" href="Netplex_encap.html">
<link title="Netplex_mbox" rel="Chapter" href="Netplex_mbox.html">
<link title="Netplex_internal" rel="Chapter" href="Netplex_internal.html">
<link title="Netplex_intro" rel="Chapter" href="Netplex_intro.html">
<link title="Netplex_advanced" rel="Chapter" href="Netplex_advanced.html">
<link title="Netplex_admin" rel="Chapter" href="Netplex_admin.html">
<link title="Netshm" rel="Chapter" href="Netshm.html">
<link title="Netshm_data" rel="Chapter" href="Netshm_data.html">
<link title="Netshm_hashtbl" rel="Chapter" href="Netshm_hashtbl.html">
<link title="Netshm_array" rel="Chapter" href="Netshm_array.html">
<link title="Netshm_intro" rel="Chapter" href="Netshm_intro.html">
<link title="Netstring_pcre" rel="Chapter" href="Netstring_pcre.html">
<link title="Netconversion" rel="Chapter" href="Netconversion.html">
<link title="Netchannels" rel="Chapter" href="Netchannels.html">
<link title="Netstream" rel="Chapter" href="Netstream.html">
<link title="Netmime_string" rel="Chapter" href="Netmime_string.html">
<link title="Netmime" rel="Chapter" href="Netmime.html">
<link title="Netsendmail" rel="Chapter" href="Netsendmail.html">
<link title="Neturl" rel="Chapter" href="Neturl.html">
<link title="Netaddress" rel="Chapter" href="Netaddress.html">
<link title="Netbuffer" rel="Chapter" href="Netbuffer.html">
<link title="Netmime_header" rel="Chapter" href="Netmime_header.html">
<link title="Netmime_channels" rel="Chapter" href="Netmime_channels.html">
<link title="Neturl_ldap" rel="Chapter" href="Neturl_ldap.html">
<link title="Netdate" rel="Chapter" href="Netdate.html">
<link title="Netencoding" rel="Chapter" href="Netencoding.html">
<link title="Netulex" rel="Chapter" href="Netulex.html">
<link title="Netaccel" rel="Chapter" href="Netaccel.html">
<link title="Netaccel_link" rel="Chapter" href="Netaccel_link.html">
<link title="Nethtml" rel="Chapter" href="Nethtml.html">
<link title="Netstring_str" rel="Chapter" href="Netstring_str.html">
<link title="Netmappings" rel="Chapter" href="Netmappings.html">
<link title="Netaux" rel="Chapter" href="Netaux.html">
<link title="Nethttp" rel="Chapter" href="Nethttp.html">
<link title="Netpagebuffer" rel="Chapter" href="Netpagebuffer.html">
<link title="Netfs" rel="Chapter" href="Netfs.html">
<link title="Netglob" rel="Chapter" href="Netglob.html">
<link title="Netauth" rel="Chapter" href="Netauth.html">
<link title="Netsockaddr" rel="Chapter" href="Netsockaddr.html">
<link title="Netnumber" rel="Chapter" href="Netnumber.html">
<link title="Netxdr_mstring" rel="Chapter" href="Netxdr_mstring.html">
<link title="Netxdr" rel="Chapter" href="Netxdr.html">
<link title="Netcompression" rel="Chapter" href="Netcompression.html">
<link title="Netunichar" rel="Chapter" href="Netunichar.html">
<link title="Netasn1" rel="Chapter" href="Netasn1.html">
<link title="Netasn1_encode" rel="Chapter" href="Netasn1_encode.html">
<link title="Netoid" rel="Chapter" href="Netoid.html">
<link title="Netstring_tstring" rel="Chapter" href="Netstring_tstring.html">
<link title="Netdn" rel="Chapter" href="Netdn.html">
<link title="Netx509" rel="Chapter" href="Netx509.html">
<link title="Netascii_armor" rel="Chapter" href="Netascii_armor.html">
<link title="Nettls_support" rel="Chapter" href="Nettls_support.html">
<link title="Netmech_scram" rel="Chapter" href="Netmech_scram.html">
<link title="Netmech_scram_gssapi" rel="Chapter" href="Netmech_scram_gssapi.html">
<link title="Netmech_scram_sasl" rel="Chapter" href="Netmech_scram_sasl.html">
<link title="Netmech_scram_http" rel="Chapter" href="Netmech_scram_http.html">
<link title="Netgssapi_support" rel="Chapter" href="Netgssapi_support.html">
<link title="Netgssapi_auth" rel="Chapter" href="Netgssapi_auth.html">
<link title="Netchannels_crypto" rel="Chapter" href="Netchannels_crypto.html">
<link title="Netx509_pubkey" rel="Chapter" href="Netx509_pubkey.html">
<link title="Netx509_pubkey_crypto" rel="Chapter" href="Netx509_pubkey_crypto.html">
<link title="Netsaslprep" rel="Chapter" href="Netsaslprep.html">
<link title="Netmech_plain_sasl" rel="Chapter" href="Netmech_plain_sasl.html">
<link title="Netmech_crammd5_sasl" rel="Chapter" href="Netmech_crammd5_sasl.html">
<link title="Netmech_digest_sasl" rel="Chapter" href="Netmech_digest_sasl.html">
<link title="Netmech_digest_http" rel="Chapter" href="Netmech_digest_http.html">
<link title="Netmech_krb5_sasl" rel="Chapter" href="Netmech_krb5_sasl.html">
<link title="Netmech_gs2_sasl" rel="Chapter" href="Netmech_gs2_sasl.html">
<link title="Netmech_spnego_http" rel="Chapter" href="Netmech_spnego_http.html">
<link title="Netchannels_tut" rel="Chapter" href="Netchannels_tut.html">
<link title="Netmime_tut" rel="Chapter" href="Netmime_tut.html">
<link title="Netsendmail_tut" rel="Chapter" href="Netsendmail_tut.html">
<link title="Netulex_tut" rel="Chapter" href="Netulex_tut.html">
<link title="Neturl_tut" rel="Chapter" href="Neturl_tut.html">
<link title="Netsys" rel="Chapter" href="Netsys.html">
<link title="Netsys_posix" rel="Chapter" href="Netsys_posix.html">
<link title="Netsys_pollset" rel="Chapter" href="Netsys_pollset.html">
<link title="Netlog" rel="Chapter" href="Netlog.html">
<link title="Netexn" rel="Chapter" href="Netexn.html">
<link title="Netsys_win32" rel="Chapter" href="Netsys_win32.html">
<link title="Netsys_pollset_posix" rel="Chapter" href="Netsys_pollset_posix.html">
<link title="Netsys_pollset_win32" rel="Chapter" href="Netsys_pollset_win32.html">
<link title="Netsys_pollset_generic" rel="Chapter" href="Netsys_pollset_generic.html">
<link title="Netsys_signal" rel="Chapter" href="Netsys_signal.html">
<link title="Netsys_oothr" rel="Chapter" href="Netsys_oothr.html">
<link title="Netsys_xdr" rel="Chapter" href="Netsys_xdr.html">
<link title="Netsys_rng" rel="Chapter" href="Netsys_rng.html">
<link title="Netsys_crypto_types" rel="Chapter" href="Netsys_crypto_types.html">
<link title="Netsys_types" rel="Chapter" href="Netsys_types.html">
<link title="Netsys_mem" rel="Chapter" href="Netsys_mem.html">
<link title="Netsys_tmp" rel="Chapter" href="Netsys_tmp.html">
<link title="Netsys_sem" rel="Chapter" href="Netsys_sem.html">
<link title="Netsys_pmanage" rel="Chapter" href="Netsys_pmanage.html">
<link title="Netsys_crypto" rel="Chapter" href="Netsys_crypto.html">
<link title="Netsys_tls" rel="Chapter" href="Netsys_tls.html">
<link title="Netsys_ciphers" rel="Chapter" href="Netsys_ciphers.html">
<link title="Netsys_digests" rel="Chapter" href="Netsys_digests.html">
<link title="Netsys_crypto_modes" rel="Chapter" href="Netsys_crypto_modes.html">
<link title="Netsys_gssapi" rel="Chapter" href="Netsys_gssapi.html">
<link title="Netsys_sasl_types" rel="Chapter" href="Netsys_sasl_types.html">
<link title="Netsys_sasl" rel="Chapter" href="Netsys_sasl.html">
<link title="Netsys_polypipe" rel="Chapter" href="Netsys_polypipe.html">
<link title="Netsys_polysocket" rel="Chapter" href="Netsys_polysocket.html">
<link title="Netsys_global" rel="Chapter" href="Netsys_global.html">
<link title="Nettls_gnutls_bindings" rel="Chapter" href="Nettls_gnutls_bindings.html">
<link title="Nettls_nettle_bindings" rel="Chapter" href="Nettls_nettle_bindings.html">
<link title="Nettls_gnutls" rel="Chapter" href="Nettls_gnutls.html">
<link title="Netunidata" rel="Chapter" href="Netunidata.html">
<link title="Netgzip" rel="Chapter" href="Netgzip.html">
<link title="Rpc_auth_local" rel="Chapter" href="Rpc_auth_local.html">
<link title="Rpc_xti_client" rel="Chapter" href="Rpc_xti_client.html">
<link title="Rpc" rel="Chapter" href="Rpc.html">
<link title="Rpc_program" rel="Chapter" href="Rpc_program.html">
<link title="Rpc_util" rel="Chapter" href="Rpc_util.html">
<link title="Rpc_portmapper_aux" rel="Chapter" href="Rpc_portmapper_aux.html">
<link title="Rpc_packer" rel="Chapter" href="Rpc_packer.html">
<link title="Rpc_transport" rel="Chapter" href="Rpc_transport.html">
<link title="Rpc_client" rel="Chapter" href="Rpc_client.html">
<link title="Rpc_simple_client" rel="Chapter" href="Rpc_simple_client.html">
<link title="Rpc_portmapper_clnt" rel="Chapter" href="Rpc_portmapper_clnt.html">
<link title="Rpc_portmapper" rel="Chapter" href="Rpc_portmapper.html">
<link title="Rpc_server" rel="Chapter" href="Rpc_server.html">
<link title="Rpc_auth_sys" rel="Chapter" href="Rpc_auth_sys.html">
<link title="Rpc_auth_gssapi" rel="Chapter" href="Rpc_auth_gssapi.html">
<link title="Rpc_proxy" rel="Chapter" href="Rpc_proxy.html">
<link title="Rpc_intro" rel="Chapter" href="Rpc_intro.html">
<link title="Rpc_mapping_ref" rel="Chapter" href="Rpc_mapping_ref.html">
<link title="Rpc_intro_gss" rel="Chapter" href="Rpc_intro_gss.html">
<link title="Shell_sys" rel="Chapter" href="Shell_sys.html">
<link title="Shell" rel="Chapter" href="Shell.html">
<link title="Shell_uq" rel="Chapter" href="Shell_uq.html">
<link title="Shell_fs" rel="Chapter" href="Shell_fs.html">
<link title="Shell_intro" rel="Chapter" href="Shell_intro.html">
<link title="Intro" rel="Chapter" href="Intro.html">
<link title="Platform" rel="Chapter" href="Platform.html">
<link title="Foreword" rel="Chapter" href="Foreword.html">
<link title="Ipv6" rel="Chapter" href="Ipv6.html">
<link title="Regexp" rel="Chapter" href="Regexp.html">
<link title="Tls" rel="Chapter" href="Tls.html">
<link title="Crypto" rel="Chapter" href="Crypto.html">
<link title="Authentication" rel="Chapter" href="Authentication.html">
<link title="Credentials" rel="Chapter" href="Credentials.html">
<link title="Gssapi" rel="Chapter" href="Gssapi.html">
<link title="Ocamlnet4" rel="Chapter" href="Ocamlnet4.html">
<link title="Get" rel="Chapter" href="Get.html"><title>Ocamlnet 4 Reference Manual : Platform</title>
</head>
<body>
<div class="navbar"><a class="pre" href="Intro.html" title="Intro">Previous</a>
<a class="up" href="index.html" title="Index">Up</a>
<a class="post" href="Foreword.html" title="Foreword">Next</a>
</div>
<h1>Platform</h1>
<div class="info-desc">
<h2 id="1_PlatformSupport">Platform Support</h2>
<p>Not everything works in the same way for all operating systems. This
documents describes the different levels of support for the various
platforms.</p>
<h3 id="2_POSIX">POSIX</h3>
<p>Ocamlnet has been primarily developed for POSIX systems. Most libraries
should work on all systems, but there are also some more special features
that are designed for certain systems only.</p>
<h4 id="3_Banningselect">Banning <code class="code">select()</code></h4>
<p>On POSIX systems, the <code class="code">select()</code> system call is not used anymore. As
a general-purpose replacement Ocamlnet favors <code class="code">poll()</code>. In future
versions of Ocamlnet, there will also be support for the improved
versions of <code class="code">poll()</code> some systems provide, such as <code class="code">epoll</code> on Linux,
<code class="code">kqueue</code> on BSD, and <code class="code">/dev/poll</code> on Solaris. Ocamlnet is already
prepared for this change.</p>
<p>The reason for banning <code class="code">select()</code> are the limited capabilities of this
API. Especially, it cannot handle file descriptors whose numeric
values exceed a system-dependent limit. Although this limit is quite
high (usually 1024) there are applications that need more descriptors.
(Note that it is not sufficient to simply increase the maximum number
of descriptors a process can have - the <code class="code">select()</code> call is still
restricted in the mentioned sense, and this seems to be unfixable.)
The <code class="code">poll()</code> interface does not have this problem.</p>
<p>The <code class="code">poll()</code> interface is made accessible from Ocaml in
<a href="Netsys_posix.html"><code class="code">Netsys_posix</code></a>.</p>
<h4 id="3_Multiprocessingandfork">Multi-processing and <code class="code">fork()</code></h4>
<p>One of the main difference of the POSIX platforms compared with
Windows is that there is the <code class="code">fork()</code> system call. Ocamlnet provides
multi-processing support in the <code class="code">netplex</code> library (see <a href="Netplex_mp.html"><code class="code">Netplex_mp</code></a>).
This makes it easy to manage a set of child processes that are used
as parallel running "workers" (e.g. for accepting network connections).</p>
<p>There is a registry of user functions to be run after a new child
process has been forked off (see
<a href="Netsys_posix.html#VALregister_post_fork_handler"><code class="code">Netsys_posix.register_post_fork_handler</code></a>). The intention is that the
child can close descriptors it would otherwise share with the parent.</p>
<p>One should note that there is a basic incompatibility between code
that uses <code class="code">fork()</code> to achieve parallelism and multi-threading. The
problem is that the state of synchronization objects like mutexes is
undefined after <code class="code">fork()</code>. In the C language, one can try to define
special handlers that run before/after the <code class="code">fork()</code> to fix up such
objects. There is no such possibility in Ocaml (the mentioned
registry cannot be used for this purpose). One simply should not call
<code class="code">fork()</code> while there is more than one thread. It is of course allowed
to start threads in the sub processes.</p>
<p>For the multi-processing capability of <code class="code">netplex</code> this means that one
must not create threads in the master process (from which the worker
processes are forked off). There is no such restriction for the
children.</p>
<h4 id="3_Startingprogramsassubprocesses">Starting programs as sub processes</h4>
<p>There is now extended support for starting subprograms. First, there
is <a href="Netsys_posix.html#VALspawn"><code class="code">Netsys_posix.spawn</code></a> which provides a comfortable way for starting
programs. The interface is patterned after the <code class="code">posix_spawn()</code> system
call although the implemention is not using <code class="code">posix_spawn()</code> yet, but
a traditional <code class="code">fork/exec</code> combination.
(In a later version of Ocamlnet it is planned to give the user the
choice of using <code class="code">posix_spawn()</code> as the underlying system interface.
On some OS, <code class="code">posix_spawn()</code> is highly optimized and significantly
faster than <code class="code">fork/exec</code>.)</p>
<p>Second, it is now possible to let Ocamlnet watch for the termination
of child processes: <a href="Netsys_posix.html#VALwatch_subprocess"><code class="code">Netsys_posix.watch_subprocess</code></a>. This function
arranges that the <code class="code">SIGCHLD</code> signal is caught, and that the process
termination is reported as a file descriptor event. By means of
careful programming this even works for multi-threaded applications
(where signal handling is notoriously difficult).</p>
<h4 id="3_RPCintegration">RPC integration</h4>
<p>POSIX systems usually already provide RPC functionality, as some
deeply-integrated networking protocols like NFS are based on it.
Traditionally, there is a program called <code class="code">portmapper</code> that acts as
registry of RPC services running on a machine. Ocamlnet can register
servers in <code class="code">portmapper</code>, and it can also look up services there.</p>
<p>On some systems, there is a newer version of <code class="code">portmapper</code> called
<code class="code">rpcbind</code>. Fortunately, <code class="code">rpcbind</code> is backward-compatible, and also
provides a <code class="code">portmapper</code>-style interface.</p>
<p>There is some problem, though, on systems that also provide the XTI
networking API which is a replacement for the socket API. Whereas
TCP/IP can be used with both XTI and sockets, the local network
connections the API's provide are incompatible: A local XTI endpoint
cannot be contacted over the socket API, and a local socket endpoint
(i.e. a Unix domain socket) cannot be contacted over XTI. There is
the helper library <a href="Rpc_xti_client.html"><code class="code">Rpc_xti_client</code></a> that allows to connect to a local
XTI server.</p>
<h3 id="2_Windows">Windows</h3>
<h4 id="3_Cygwin">Cygwin</h4>
<p>On Cygwin Ocamlnet should behave like on a POSIX machine.</p>
<h4 id="3_Win32">Win32</h4>
<p><b>General remark:</b> The Win32 port is still very experimental, and
far from being bug-free! Development progresses very slowly. Please
don't expect wonders.</p>
<p>There is now a lot of support for Win32, even for asynchronous network
programming. The minimum Windows version is Windows XP SP2. One should
also mention that some functions are only supported when the Ocaml
program is compiled as multi-threaded program, as sometimes helper
threads are needed to emulate a certain behavior. For example, Win32
limits the number of file handles to 64 per thread when one watches
them for events. Ocamlnet includes support to overcome this limit by
creating helper threads as needed.</p>
<p>As a substitute for Unix Domain sockets, Ocamlnet provides access to
Win32 named pipes. These are, for security reasons, restricted to
local connection (within the same machine). As named pipes exist in a
special file system, one cannot create named pipes in arbitrary
directories (unlike Unix Domain sockets). As a workaround, it is also
supported to create named pipes with random names, and to write these
names into text files. A number of functions that used to expect Unix
Domain socket files as input can now also deal with these text files,
and will automatically map these files to the referenced named pipes
(see <a href="Netplex_sockserv.html#VALany_file_client_connector"><code class="code">Netplex_sockserv.any_file_client_connector</code></a>).</p>
<p>The <b>RPC</b> implementation supports TCP/IP sockets and named pipes,
both for clients and for servers. As for POSIX, the clients and servers
can be programmed in an asynchronous way.</p>
<p><b>Netplex</b> is supported, but only for multi-threaded containers. The
multi-processing containers are not available. Netplex can manage both
TCP connections and named pipes.</p>
<p>The <b>Shell</b> library works, too. As for POSIX, it is possible to
create complex pipelines between the started shell commands, and it is
possible to read the output of and to provide input to the commands at
the same time. All asynchronous command execution features are
available! The only limitation is that one can redirect only
stdin/stdout/stderr of the started commands, and not arbitrary
descriptors as for POSIX (this is a restriction of Win32).</p>
<p>The <b>Equeue</b> library is supported. The GTK- and TclTk-specific
extensions do not work, however. The SSL add-on is untested.</p>
<p>The <b>Netshm</b> library is only partially supported: The managed memory
object must be file-backed and cannot (yet) live in RAM-only shared
memory.</p>
<p>The <b>Nethttpd</b> library is fully supported.</p>
<p>XXX: Netcgi2</p>
<h4 id="3_Win32lowlevel">Win32 low-level</h4>
<p>The missing Win32 calls are made available via <a href="Netsys_win32.html"><code class="code">Netsys_win32</code></a>. The
accessible objects are:</p>
<ul>
<li>Events: Win32 event objects can signal a condition (and look like
condition variables)</li>
<li>Named pipes: Win32 named pipes are network connections between
a client endpoint and a server endpoint. Ocamlnet only supports
local connections, however.</li>
<li>Pipe servers: The notion
of "pipe servers" does not exist in Win32 as kernel objects. Win32
sees a pipe server as a set of endpoints one can connect to, and the
user code has to manage this set. In <a href="Netsys_win32.html"><code class="code">Netsys_win32</code></a>, pipe server
objects are emulated to simplify this for user code, so that pipe
servers look very much like socket servers.</li>
<li>Input threads: <a href="Netsys_win32.html"><code class="code">Netsys_win32</code></a> provides helper threads allowing one to
read from an arbitrary file handle in an asynchronous way, even if Win32
does not support that for the type of handle. This is intended for
reading from anonymous pipes (as returned by <code class="code">Unix.pipe</code>).</li>
<li>Output threads: a similar kind of object writing to file handles</li>
<li>Processes</li>
<li>Consoles</li>
</ul>
<p>As you can see, we are trying to make the Win32 calls a bit more user
friendly. One of the goals of this wrapper is to make them even usable
in programs that are mainly written for POSIX.</p>
<p>A central idea here is the concept of "proxy descriptors". Many of the
mentioned objects have a complex inner structure - e.g. a pipe server
can mean an open number of Win32 file handles. However, it is intended
to make these objects look like in POSIX, and that means that there is
only a single descriptor referencing the object. The proxy descriptors
are additional file descriptors Ocamlnet allocates only for the purpose
of referencing these objects. For example, a pipe server is mainly
represented by the type <a href="Netsys_win32.html#TYPEw32_pipe_server"><code class="code">Netsys_win32.w32_pipe_server</code></a>, and there are
a lot of functions dealing with such values, e.g.
<a href="Netsys_win32.html#VALpipe_shutdown_server"><code class="code">Netsys_win32.pipe_shutdown_server</code></a> for shutting a server down.
Of course, a <a href="Netsys_win32.html#TYPEw32_pipe_server"><code class="code">Netsys_win32.w32_pipe_server</code></a> is not a file descriptor,
but a complex Ocaml record. The question is now how to pass such an
object to functions that only accept file descriptors as input? The
solution looks simple although the implementation causes a lot of
headache: A special file descriptor is allocated, and there is a global
table mapping these descriptors to the real objects. For instance, you
can get the proxy descriptor of a pipe server by calling</p>
<pre class="codepre"><code class="code"> let (fd : Unix.file_descr) =
Netsys_win32.pipe_server_descr psrv
</code></pre>
<p>for a pipe server object <code class="code">psrv</code>. You can pass <code class="code">fd</code> around, and when
a called function requires the pipe server object again, one can
map <code class="code">fd</code> back by:</p>
<pre class="codepre"><code class="code"> let (psrv : Netsys_win32.w32_pipe_server) =
Netsys_win32.lookup_pipe_server fd
</code></pre>
<p>Like other descriptors, <code class="code">fd</code> must be closed after use. The tricky part
of the implementation is that unreferenced proxy descriptors are
detected, and that the entry of the global mapping table is deleted
then.</p>
<p>As mentioned, Ocamlnet supports asynchronous I/O for the supported
Win32 objects. For some objects, Win32 has built-in support in the
form of so-called overlapped I/O. This kind of I/O is, unfortunately,
different than what POSIX provides (<code class="code">poll</code>-style I/O). The analysis
shows that the main difference is that in Win32 one has to start an
I/O operation in order to asynchronously check whether and when it is
finally possible, whereas POSIX allows one to check the possibility of
I/O before one starts the operation. Ocamlnet hides this difference in
the <a href="Netsys_win32.html"><code class="code">Netsys_win32</code></a> wrapper by providing additional buffering. The
price is, however, that the generic <code class="code">read</code> and <code class="code">write</code> calls (or
better, <code class="code">ReadFile</code> and <code class="code">WriteFile</code> in Win32) can no longer be used.
As a substitute, Ocamlnet provides for each kind of object a special
set of read and write operations, e.g. <a href="Netsys_win32.html#VALpipe_read"><code class="code">Netsys_win32.pipe_read</code></a>
for named pipes.</p>
<p>For simplicity of user code, there are also generalized read/write
operations: <a href="Netsys.html#VALgread"><code class="code">Netsys.gread</code></a> and <a href="Netsys.html#VALgwrite"><code class="code">Netsys.gwrite</code></a>. These work for
all descriptors supported by <code class="code">Unix.read</code> and <code class="code">Unix.write</code>, plus for
sockets, plus for all of the mentioned Win32-specific objects for
which reading and writing are reasonable I/O operations.</p>
<p>If overlapping I/O is unavailable for a kind of file handle, it is
still possible to use the input and output threads in order to do
asynchronous I/O for these handles. An example of such a handle type
are anonymous pipes. The threads are automatically started and
initiate synchronous I/O operations when needed. The completion of the
operations is signalled via condition variables to the caller, so that
it is possible to provide an asynchronous API to the file handle.</p>
<h3 id="2_Hintsforportableprogramming">Hints for portable programming</h3>
<p>Generally, the functions in <a href="Netsys.html"><code class="code">Netsys</code></a> are available on all platforms
(but not necessarily in all variants), whereas <a href="Netsys_posix.html"><code class="code">Netsys_posix</code></a> and
<a href="Netsys_win32.html"><code class="code">Netsys_win32</code></a> contain the platform-specific stuff.</p>
<p>In order to read and write file descriptors, one should first get
the kind of descriptor <code class="code">fd</code>:</p>
<pre class="codepre"><code class="code"> let st = Netsys.get_fd_style fd </code></pre>
<p>Now, one can read and write to the file descriptor by calling
<a href="Netsys.html#VALgread"><code class="code">Netsys.gread</code></a> and <a href="Netsys.html#VALgwrite"><code class="code">Netsys.gwrite</code></a> (or by some of the provided
variants of these functions). These functions need <code class="code">st</code> as input,
and internally call the right system function to do the requested
I/O operation.</p>
<p>There is also <a href="Netsys.html#VALgshutdown"><code class="code">Netsys.gshutdown</code></a> for shutting a descriptor down
(possibly only half-way), and <a href="Netsys.html#VALgclose"><code class="code">Netsys.gclose</code></a> for closing a
descriptor.</p>
<p>In order to wait for a <b>single</b> descriptor, one can call one of the
<a href="Netsys.html"><code class="code">Netsys</code></a> functions doing so, e.g. <a href="Netsys.html#VALwait_until_readable"><code class="code">Netsys.wait_until_readable</code></a>.
These functions block execution until the requested I/O operation
is possible, or until a timeout elapses.</p>
<p>If <b>several</b> descriptors need to be waited for, there is the
portable class type <a href="Netsys_pollset.pollset-c.html"><code class="code">Netsys_pollset.pollset</code></a>. One can add several
descriptors to pollsets and wait until I/O operations for one of the
descriptors become possible. There are implementations for both POSIX
and Win32. <a href="Netsys_pollset_generic.html#VALstandard_pollset"><code class="code">Netsys_pollset_generic.standard_pollset</code></a> automatically
selects the best pollset implementation for "normal use".</p>
<p>For porting programs that are still written around <code class="code">Unix.select</code>,
there is an emulation of <code class="code">select</code> on top of pollsets:
<a href="Netsys_pollset_generic.html#VALselect_emulation"><code class="code">Netsys_pollset_generic.select_emulation</code></a>.</p>
</div>
</body></html>
|
