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
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<HTML>
<HEAD>
<TITLE>AARM95 - Entries and Accept Statements</TITLE>
<META NAME="Author" CONTENT="JTC1/SC22/WG9/ARG, by Randall Brukardt, ARG Editor">
<META NAME="GENERATOR" CONTENT="Arm_Form.Exe, Ada Reference Manual generator">
<STYLE type="text/css">
DIV.paranum {position: absolute; font-family: Arial, Helvetica, sans-serif; left: 0.5 em; top: auto}
TT {font-family: "Courier New", monospace}
DT {display: compact}
DIV.Normal {font-family: "Times New Roman", Times, serif; margin-bottom: 0.6em}
DIV.Wide {font-family: "Times New Roman", Times, serif; margin-top: 0.6em; margin-bottom: 0.6em}
DIV.Annotations {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-bottom: 0.6em}
DIV.WideAnnotations {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-top: 0.6em; margin-bottom: 0.6em}
DIV.Index {font-family: "Times New Roman", Times, serif}
DIV.SyntaxSummary {font-family: "Times New Roman", Times, serif; margin-left: 2.0em; margin-bottom: 0.4em}
DIV.Notes {font-family: "Times New Roman", Times, serif; margin-left: 2.0em; margin-bottom: 0.6em}
DIV.NotesHeader {font-family: "Times New Roman", Times, serif; margin-left: 2.0em}
DIV.SyntaxIndented {font-family: "Times New Roman", Times, serif; margin-left: 2.0em; margin-bottom: 0.4em}
DIV.Indented {font-family: "Times New Roman", Times, serif; margin-left: 6.0em; margin-bottom: 0.6em}
DIV.CodeIndented {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-bottom: 0.6em}
DIV.SmallIndented {font-family: "Times New Roman", Times, serif; margin-left: 10.0em; margin-bottom: 0.6em}
DIV.SmallCodeIndented {font-family: "Times New Roman", Times, serif; margin-left: 8.0em; margin-bottom: 0.6em}
DIV.Examples {font-family: "Courier New", monospace; margin-left: 2.0em; margin-bottom: 0.6em}
DIV.SmallExamples {font-family: "Courier New", monospace; font-size: 80%; margin-left: 7.5em; margin-bottom: 0.6em}
DIV.IndentedExamples {font-family: "Courier New", monospace; margin-left: 8.0em; margin-bottom: 0.6em}
DIV.SmallIndentedExamples {font-family: "Courier New", monospace; font-size: 80%; margin-left: 15.0em; margin-bottom: 0.6em}
UL.Bulleted {font-family: "Times New Roman", Times, serif; margin-left: 2.0em; margin-right: 2.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.SmallBulleted {font-family: "Times New Roman", Times, serif; margin-left: 6.0em; margin-right: 6.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.NestedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-right: 4.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.SmallNestedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 8.0em; margin-right: 8.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.IndentedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 8.0em; margin-right: 8.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.CodeIndentedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 6.0em; margin-right: 6.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.CodeIndentedNestedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 8.0em; margin-right: 8.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.SyntaxIndentedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-right: 4.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.NotesBulleted {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-right: 4.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.NotesNestedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 6.0em; margin-right: 6.0em; margin-top: 0em; margin-bottom: 0.5em}
DL.Hanging {font-family: "Times New Roman", Times, serif; margin-top: 0em; margin-bottom: 0.6em}
DD.Hanging {margin-left: 6.0em}
DL.IndentedHanging {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-top: 0em; margin-bottom: 0.6em}
DD.IndentedHanging {margin-left: 2.0em}
DL.HangingInBulleted {font-family: "Times New Roman", Times, serif; margin-left: 2.0em; margin-right: 2.0em; margin-top: 0em; margin-bottom: 0.5em}
DD.HangingInBulleted {margin-left: 4.0em}
DL.SmallHanging {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-top: 0em; margin-bottom: 0.6em}
DD.SmallHanging {margin-left: 7.5em}
DL.SmallIndentedHanging {font-family: "Times New Roman", Times, serif; margin-left: 8.0em; margin-top: 0em; margin-bottom: 0.6em}
DD.SmallIndentedHanging {margin-left: 2.0em}
DL.SmallHangingInBulleted {font-family: "Times New Roman", Times, serif; margin-left: 6.0em; margin-right: 6.0em; margin-top: 0em; margin-bottom: 0.5em}
DD.SmallHangingInBulleted {margin-left: 5.0em}
DL.Enumerated {font-family: "Times New Roman", Times, serif; margin-right: 0.0em; margin-top: 0em; margin-bottom: 0.5em}
DD.Enumerated {margin-left: 2.0em}
DL.SmallEnumerated {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-right: 4.0em; margin-top: 0em; margin-bottom: 0.5em}
DD.SmallEnumerated {margin-left: 2.5em}
DL.NestedEnumerated {font-family: "Times New Roman", Times, serif; margin-left: 2.0em; margin-right: 2.0em; margin-top: 0em; margin-bottom: 0.5em}
DL.SmallNestedEnumerated {font-family: "Times New Roman", Times, serif; margin-left: 6.0em; margin-right: 6.0em; margin-top: 0em; margin-bottom: 0.5em}
</STYLE>
</HEAD>
<BODY TEXT="#000000" BGCOLOR="#FFFFF0" LINK="#0000FF" VLINK="#800080" ALINK="#FF0000">
<P><A HREF="AA-TOC.html">Contents</A> <A HREF="AA-0-29.html">Index</A> <A HREF="AA-9-5-1.html">Previous</A> <A HREF="AA-9-5-3.html">Next</A></P>
<HR>
<H1> 9.5.2 Entries and Accept Statements</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> <FONT FACE="Arial, Helvetica">Entry_declaration</FONT>s,
with the corresponding <FONT FACE="Arial, Helvetica">entry_bodies</FONT>
or <FONT FACE="Arial, Helvetica">accept_statement</FONT>s, are used to
define potentially queued operations on tasks and protected objects.
</DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">entry_declaration<A NAME="I3597"></A>
::= </FONT><BR>
<B>entry</B> <A NAME="I3598"></A><FONT FACE="Arial, Helvetica">defining_identifier</FONT> [(<A NAME="I3599"></A><FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>)] <A NAME="I3600"></A><FONT FACE="Arial, Helvetica">parameter_profile</FONT>;</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">accept_statement<A NAME="I3601"></A>
::= </FONT><BR>
<B>accept</B> <I>entry_</I><A NAME="I3602"></A><FONT FACE="Arial, Helvetica">direct_name</FONT> [(<A NAME="I3603"></A><FONT FACE="Arial, Helvetica">entry_index</FONT>)] <A NAME="I3604"></A><FONT FACE="Arial, Helvetica">parameter_profile</FONT> [<B>do</B><BR>
<A NAME="I3605"></A><FONT FACE="Arial, Helvetica">handled_sequence_of_statements</FONT><BR>
<B>end</B> [<I>entry_</I><A NAME="I3606"></A><FONT FACE="Arial, Helvetica">identifier</FONT>]];</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Reason: </B>We cannot use <FONT FACE="Arial, Helvetica">defining_identifier</FONT>
for <FONT FACE="Arial, Helvetica">accept_statement</FONT>s. Although
an <FONT FACE="Arial, Helvetica">accept_statement</FONT> is sort of like
a body, it can appear nested within a <FONT FACE="Arial, Helvetica">block_statement</FONT>,
and therefore be hidden from its own entry by an outer homograph. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">entry_index<A NAME="I3607"></A>
::= </FONT><A NAME="I3608"></A><FONT FACE="Arial, Helvetica">expression</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">entry_body<A NAME="I3609"></A>
::= </FONT><BR>
<B>entry</B> <A NAME="I3610"></A><FONT FACE="Arial, Helvetica">defining_identifier</FONT> <A NAME="I3611"></A><FONT FACE="Arial, Helvetica">entry_body_formal_part</FONT> <A NAME="I3612"></A><FONT FACE="Arial, Helvetica">entry_barrier</FONT> <B>is</B><BR>
<A NAME="I3613"></A><FONT FACE="Arial, Helvetica">declarative_part</FONT><BR>
<B>begin</B><BR>
<A NAME="I3614"></A><FONT FACE="Arial, Helvetica">handled_sequence_of_statements</FONT><BR>
<B>end</B> [<I>entry_</I><A NAME="I3615"></A><FONT FACE="Arial, Helvetica">identifier</FONT>];</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">entry_body_formal_part<A NAME="I3616"></A>
::= </FONT>[(<A NAME="I3617"></A><FONT FACE="Arial, Helvetica">entry_index_specification</FONT>)] <A NAME="I3618"></A><FONT FACE="Arial, Helvetica">parameter_profile</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">entry_barrier<A NAME="I3619"></A>
::= </FONT><B>when</B> <A NAME="I3620"></A><FONT FACE="Arial, Helvetica">condition</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">entry_index_specification<A NAME="I3621"></A>
::= </FONT><B>for</B> <A NAME="I3622"></A><FONT FACE="Arial, Helvetica">defining_identifier</FONT> <B>in</B> <A NAME="I3623"></A><FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="SyntaxIndented">If an <I>entry_</I><FONT FACE="Arial, Helvetica">identifier</FONT>
appears at the end of an <FONT FACE="Arial, Helvetica">accept_statement</FONT>,
it shall repeat the <I>entry_</I><FONT FACE="Arial, Helvetica">direct_name</FONT>.
If an <I>entry_</I><FONT FACE="Arial, Helvetica">identifier</FONT> appears
at the end of an <FONT FACE="Arial, Helvetica">entry_body</FONT>, it
shall repeat the <FONT FACE="Arial, Helvetica">defining_identifier</FONT>.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="SyntaxIndented">[An <FONT FACE="Arial, Helvetica">entry_declaration</FONT>
is allowed only in a protected or task declaration.] </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Proof: </B>This follows from
the BNF. </FONT></DIV>
<H4 ALIGN=CENTER>Name Resolution Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3624"></A>In an <FONT FACE="Arial, Helvetica">accept_statement</FONT>,
the expected profile for the <I>entry_</I><FONT FACE="Arial, Helvetica">direct_name</FONT>
is that of the <FONT FACE="Arial, Helvetica">entry_declaration</FONT>;
<A NAME="I3625"></A>the expected type for an <FONT FACE="Arial, Helvetica">entry_index</FONT>
is that of the subtype defined by the <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>
of the corresponding <FONT FACE="Arial, Helvetica">entry_declaration</FONT>.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Normal"> Within the <FONT FACE="Arial, Helvetica">handled_sequence_of_statements</FONT>
of an <FONT FACE="Arial, Helvetica">accept_statement</FONT>, if a <FONT FACE="Arial, Helvetica">selected_component</FONT>
has a <FONT FACE="Arial, Helvetica">prefix</FONT> that denotes the corresponding
<FONT FACE="Arial, Helvetica">entry_declaration</FONT>, then the entity
denoted by the <FONT FACE="Arial, Helvetica">prefix</FONT> is the <FONT FACE="Arial, Helvetica">accept_statement</FONT>,
and the <FONT FACE="Arial, Helvetica">selected_component</FONT> is interpreted
as an expanded name (see <A HREF="AA-4-1-3.html">4.1.3</A>)[; the <FONT FACE="Arial, Helvetica">selector_name</FONT>
of the <FONT FACE="Arial, Helvetica">selected_component</FONT> has to
be the <FONT FACE="Arial, Helvetica">identifier</FONT> for some formal
parameter of the <FONT FACE="Arial, Helvetica">accept_statement</FONT>].
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Proof: </B>The only declarations
that occur immediately within the declarative region of an <FONT FACE="Arial, Helvetica">accept_statement</FONT>
are those for its formal parameters. </FONT></DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Normal"> An <FONT FACE="Arial, Helvetica">entry_declaration</FONT>
in a task declaration shall not contain a specification for an access
parameter (see <A HREF="AA-3-10.html">3.10</A>). </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13.a</FONT></DIV>
<DIV Class="Annotations" Style="margin-bottom: 0.4em"><FONT SIZE=-1><B>Reason:
</B>Access parameters for task entries would require a complex implementation.
For example: </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13.b</FONT></DIV>
<DIV Class="SmallExamples"><TT><B>task</B> T <B>is</B><BR>
<B>entry</B> E(Z : <B>access</B> Integer); --<I> Illegal!</I><BR>
<B>end</B> T;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13.c</FONT></DIV>
<DIV Class="SmallExamples"><TT><B>task body</B> T <B>is</B><BR>
<B>begin</B><BR>
<B>declare</B><BR>
<B>type</B> A <B>is access all</B> Integer;<BR>
X : A;<BR>
Int : <B>aliased</B> Integer;<BR>
<B>task</B> Inner;<BR>
<B>task body</B> Inner <B>is</B><BR>
<B>begin</B><BR>
T.E(Int'Access);<BR>
<B>end</B> Inner;<BR>
<B>begin</B><BR>
<B>accept</B> E(Z : <B>access</B> Integer) <B>do</B><BR>
X := A(Z); -- Accessibility_Check<BR>
<B>end</B> E;<BR>
<B>end</B>;<BR>
<B>end</B> T;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13.d</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>Implementing the Accessibility_Check
inside the <FONT FACE="Arial, Helvetica">accept_statement</FONT> for
E is difficult, since one does not know whether the entry caller is calling
from inside the immediately enclosing declare block or from outside it.
This means that the lexical nesting level associated with the designated
object is not sufficient to determine whether the Accessibility_Check
should pass or fail.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13.e</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>Note that such problems do not
arise with protected entries, because <FONT FACE="Arial, Helvetica">entry_bodies</FONT>
are always nested immediately within the <FONT FACE="Arial, Helvetica">protected_body</FONT>;
they cannot be further nested as can <FONT FACE="Arial, Helvetica">accept_statement</FONT>s,
nor can they be called from within the <FONT FACE="Arial, Helvetica">protected_body</FONT>
(since no entry calls are permitted inside a <FONT FACE="Arial, Helvetica">protected_body</FONT>).
</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DIV Class="Normal"> For an <FONT FACE="Arial, Helvetica">accept_statement</FONT>,
the innermost enclosing body shall be a <FONT FACE="Arial, Helvetica">task_body</FONT>,
and the <I>entry_</I><FONT FACE="Arial, Helvetica">direct_name</FONT>
shall denote an <FONT FACE="Arial, Helvetica">entry_declaration</FONT>
in the corresponding task declaration; the profile of the <FONT FACE="Arial, Helvetica">accept_statement</FONT>
shall conform fully to that of the corresponding <FONT FACE="Arial, Helvetica">entry_declaration</FONT>.
<A NAME="I3626"></A>An <FONT FACE="Arial, Helvetica">accept_statement</FONT>
shall have a parenthesized <FONT FACE="Arial, Helvetica">entry_index</FONT>
if and only if the corresponding <FONT FACE="Arial, Helvetica">entry_declaration</FONT>
has a <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15</FONT></DIV>
<DIV Class="Normal"> An <FONT FACE="Arial, Helvetica">accept_statement</FONT>
shall not be within another <FONT FACE="Arial, Helvetica">accept_statement</FONT>
that corresponds to the same <FONT FACE="Arial, Helvetica">entry_declaration</FONT>,
nor within an <FONT FACE="Arial, Helvetica">asynchronous_select</FONT>
inner to the enclosing <FONT FACE="Arial, Helvetica">task_body</FONT>.
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Reason: </B><FONT FACE="Arial, Helvetica">Accept_statement</FONT>s
are required to be immediately within the enclosing <FONT FACE="Arial, Helvetica">task_body</FONT>
(as opposed to being in a nested subprogram) to ensure that a nested
task does not attempt to accept the entry of its enclosing task. We considered
relaxing this restriction, either by making the check a run-time check,
or by allowing a nested task to accept an entry of its enclosing task.
However, neither change seemed to provide sufficient benefit to justify
the additional implementation burden.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>Nested <FONT FACE="Arial, Helvetica">accept_statement</FONT>s
for the same entry (or entry family) are prohibited to ensure that there
is no ambiguity in the resolution of an expanded name for a formal parameter
of the entry. This could be relaxed by allowing the inner one to hide
the outer one from all visibility, but again the small added benefit
didn't seem to justify making the change for Ada 95.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15.c</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><FONT FACE="Arial, Helvetica">Accept_statement</FONT>s
are not permitted within <FONT FACE="Arial, Helvetica">asynchronous_select</FONT>
statements to simplify the semantics and implementation: an <FONT FACE="Arial, Helvetica">accept_statement</FONT>
in an <FONT FACE="Arial, Helvetica">abortable_part</FONT> could result
in Tasking_Error being propagated from an entry call even though the
target task was still callable; implementations that use multiple tasks
implicitly to implement an <FONT FACE="Arial, Helvetica">asynchronous_select</FONT>
might have trouble supporting "up-level" accepts. Furthermore,
if <FONT FACE="Arial, Helvetica">accept_statement</FONT>s were permitted
in the <FONT FACE="Arial, Helvetica">abortable_part</FONT>, a task could
call its own entry and then accept it in the <FONT FACE="Arial, Helvetica">abortable_part</FONT>,
leading to rather unusual and possibly difficult-to-specify semantics.
</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3627"></A>An <FONT FACE="Arial, Helvetica">entry_declaration</FONT>
of a protected unit requires a completion[, which shall be an <FONT FACE="Arial, Helvetica">entry_body</FONT>,]
<A NAME="I3628"></A>and every <FONT FACE="Arial, Helvetica">entry_body</FONT>
shall be the completion of an <FONT FACE="Arial, Helvetica">entry_declaration</FONT>
of a protected unit. <A NAME="I3629"></A>The profile of the <FONT FACE="Arial, Helvetica">entry_body</FONT>
shall conform fully to that of the corresponding declaration. <A NAME="I3630"></A></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>An <FONT FACE="Arial, Helvetica">entry_declaration</FONT>,
unlike a <FONT FACE="Arial, Helvetica">subprogram_declaration</FONT>,
cannot be completed with a <FONT FACE="Arial, Helvetica">renaming_declaration</FONT>.
</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>To be honest: </B>The completion
can be a <FONT FACE="Arial, Helvetica">pragma</FONT> Import, if the implementation
supports it. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16.c</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>The above applies
only to protected entries, which are the only ones completed with <FONT FACE="Arial, Helvetica">entry_bodies</FONT>.
Task entries have corresponding <FONT FACE="Arial, Helvetica">accept_statements</FONT>
instead of having <FONT FACE="Arial, Helvetica">entry_bodies</FONT>,
and we do not consider an <FONT FACE="Arial, Helvetica">accept_statement</FONT>
to be a ``completion,'' because a task <FONT FACE="Arial, Helvetica">entry_declaration</FONT>
is allowed to have zero, one, or more than one corresponding <FONT FACE="Arial, Helvetica">accept_statement</FONT>s.
</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>17</FONT></DIV>
<DIV Class="Normal"> An <FONT FACE="Arial, Helvetica">entry_body_formal_part</FONT>
shall have an <FONT FACE="Arial, Helvetica">entry_index_specification</FONT>
if and only if the corresponding <FONT FACE="Arial, Helvetica">entry_declaration</FONT>
has a <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>.
In this case, the <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>s
of the <FONT FACE="Arial, Helvetica">entry_declaration</FONT> and the
<FONT FACE="Arial, Helvetica">entry_index_specification</FONT> shall
fully conform to one another (see <A HREF="AA-6-3-1.html">6.3.1</A>).
<A NAME="I3631"></A></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>18</FONT></DIV>
<DIV Class="Normal"> A name that denotes a formal parameter of an
<FONT FACE="Arial, Helvetica">entry_body</FONT> is not allowed within
the <FONT FACE="Arial, Helvetica">entry_barrier</FONT> of the <FONT FACE="Arial, Helvetica">entry_body</FONT>.</DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>19</FONT></DIV>
<DIV Class="Normal"> The parameter modes defined for parameters in
the <FONT FACE="Arial, Helvetica">parameter_profile</FONT> of an <FONT FACE="Arial, Helvetica">entry_declaration</FONT>
are the same as for a <FONT FACE="Arial, Helvetica">subprogram_declaration</FONT>
and have the same meaning (see <A HREF="AA-6-2.html">6.2</A>). </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>19.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>Note that access
parameters are not allowed for task entries (see above). </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>20</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3632"></A><A NAME="I3633"></A><A NAME="I3634"></A>An
<FONT FACE="Arial, Helvetica">entry_declaration</FONT> with a <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>
(see <A HREF="AA-3-6.html">3.6</A>) declares a <I>family</I> of distinct
entries having the same profile, with one such entry for each value of
the <I>entry index subtype</I> defined by the <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>.
[A name for an entry of a family takes the form of an <FONT FACE="Arial, Helvetica">indexed_component</FONT>,
where the <FONT FACE="Arial, Helvetica">prefix</FONT> denotes the <FONT FACE="Arial, Helvetica">entry_declaration</FONT>
for the family, and the index value identifies the entry within the family.]
<A NAME="I3635"></A><A NAME="I3636"></A>The term <I>single entry</I>
is used to refer to any entry other than an entry of an entry family.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>21</FONT></DIV>
<DIV Class="Normal"> In the <FONT FACE="Arial, Helvetica">entry_body</FONT>
for an entry family, the <FONT FACE="Arial, Helvetica">entry_index_specification</FONT>
declares a named constant whose subtype is the entry index subtype defined
by the corresponding <FONT FACE="Arial, Helvetica">entry_declaration</FONT>;
<A NAME="I3637"></A>the value of the <I>named entry index</I> identifies
which entry of the family was called. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>21.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>The <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>
of the <FONT FACE="Arial, Helvetica">entry_index_specification</FONT>
is not elaborated; the subtype of the named constant declared is defined
by the <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>
of the corresponding <FONT FACE="Arial, Helvetica">entry_declaration</FONT>,
which is elaborated, either when the type is declared, or when the object
is created, if its constraint is per-object. </FONT></DIV>
<H4 ALIGN=CENTER>Dynamic Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>22/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0002">8652/0002</A></I>}
<A NAME="I3638"></A><U>The elaboration of an <FONT FACE="Arial, Helvetica">entry_declaration</FONT>
for an entry family consists of the elaboration of the <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>,
as described in <A HREF="AA-3-8.html">3.8</A>.</U><S>For the elaboration
of an <FONT FACE="Arial, Helvetica">entry_declaration</FONT> for an entry
family, if the <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>
contains no per-object expressions (see <A HREF="AA-3-8.html">3.8</A>),
then the <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>
is elaborated. Otherwise, the elaboration of the <FONT FACE="Arial, Helvetica">entry_declaration</FONT>
consists of the evaluation of any expression of the <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>
that is not a per-object expression (or part of one).</S> The elaboration
of an <FONT FACE="Arial, Helvetica">entry_declaration</FONT> for a single
entry has no effect. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>22.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>The elaboration
of the declaration of a protected subprogram has no effect, as specified
in clause <A HREF="AA-6-1.html">6.1</A>. The default initialization of
an object of a task or protected type is covered in <A HREF="AA-3-3-1.html">3.3.1</A>.
</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>23</FONT></DIV>
<DIV Class="Normal"> [The actions to be performed when an entry is
called are specified by the corresponding <FONT FACE="Arial, Helvetica">accept_statement</FONT>s
(if any) for an entry of a task unit, and by the corresponding <FONT FACE="Arial, Helvetica">entry_body</FONT>
for an entry of a protected unit.]</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>24</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3639"></A>For the execution of an <FONT FACE="Arial, Helvetica">accept_statement</FONT>,
the <FONT FACE="Arial, Helvetica">entry_index</FONT>, if any, is first
evaluated and converted to the entry index subtype; this index value
identifies which entry of the family is to be accepted. <A NAME="I3640"></A><A NAME="I3641"></A><A NAME="I3642"></A>Further
execution of the <FONT FACE="Arial, Helvetica">accept_statement</FONT>
is then blocked until a caller of the corresponding entry is selected
(see <A HREF="AA-9-5-3.html">9.5.3</A>), whereupon the <FONT FACE="Arial, Helvetica">handled_sequence_of_statements</FONT>,
if any, of the <FONT FACE="Arial, Helvetica">accept_statement</FONT>
is executed, with the formal parameters associated with the corresponding
actual parameters of the selected entry call. Upon completion of the
<FONT FACE="Arial, Helvetica">handled_sequence_of_statements</FONT>,
the <FONT FACE="Arial, Helvetica">accept_statement</FONT> completes and
is left. When an exception is propagated from the <FONT FACE="Arial, Helvetica">handled_sequence_of_statements</FONT>
of an <FONT FACE="Arial, Helvetica">accept_statement</FONT>, the same
exception is also raised by the execution of the corresponding <FONT FACE="Arial, Helvetica">entry_call_statement</FONT>.
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>24.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>This is in
addition to propagating it to the construct containing the <FONT FACE="Arial, Helvetica">accept_statement</FONT>.
In other words, for a rendezvous, the raising splits in two, and continues
concurrently in both tasks.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>24.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>The caller gets a new occurrence;
this isn't considered propagation.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>24.c</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>Note that we say ``propagated
from the <FONT FACE="Arial, Helvetica">handled_sequence_of_statements</FONT>
of an <FONT FACE="Arial, Helvetica">accept_statement</FONT>'', not ``propagated
from an <FONT FACE="Arial, Helvetica">accept_statement</FONT>.'' The
latter would be wrong -- we don't want exceptions propagated by the <FONT FACE="Arial, Helvetica">entry_index</FONT>
to be sent to the caller (there is none yet!). </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>25</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3643"></A>The above interaction between
a calling task and an accepting task is called a <I>rendezvous</I>. [After
a rendezvous, the two tasks continue their execution independently.]</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>26</FONT></DIV>
<DIV Class="Normal"> [An <FONT FACE="Arial, Helvetica">entry_body</FONT>
is executed when the <FONT FACE="Arial, Helvetica">condition</FONT> of
the <FONT FACE="Arial, Helvetica">entry_barrier</FONT> evaluates to True
and a caller of the corresponding single entry, or entry of the corresponding
entry family, has been selected (see <A HREF="AA-9-5-3.html">9.5.3</A>).]
<A NAME="I3644"></A>For the execution of the <FONT FACE="Arial, Helvetica">entry_body</FONT>,
the <FONT FACE="Arial, Helvetica">declarative_part</FONT> of the <FONT FACE="Arial, Helvetica">entry_body</FONT>
is elaborated, and the <FONT FACE="Arial, Helvetica">handled_sequence_of_statements</FONT>
of the body is executed, as for the execution of a <FONT FACE="Arial, Helvetica">subprogram_body</FONT>.
The value of the named entry index, if any, is determined by the value
of the entry index specified in the <I>entry_</I><FONT FACE="Arial, Helvetica">name</FONT>
of the selected entry call (or intermediate <FONT FACE="Arial, Helvetica">requeue_statement</FONT>
-- see <A HREF="AA-9-5-4.html">9.5.4</A>). </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>26.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>To be honest: </B>If the entry
had been renamed as a subprogram, and the call was a <FONT FACE="Arial, Helvetica">procedure_call_statement</FONT>
using the name declared by the renaming, the entry index (if any) comes
from the entry <FONT FACE="Arial, Helvetica">name</FONT> specified in
the <FONT FACE="Arial, Helvetica">subprogram_renaming_declaration</FONT>.
</FONT></DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>27</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>22 A task entry has corresponding
accept_statements (zero or more), whereas a protected entry has a corresponding
entry_body (exactly one).</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>28</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>23 A consequence of the rule
regarding the allowed placements of <FONT FACE="Arial, Helvetica">accept_statement</FONT>s
is that a task can execute <FONT FACE="Arial, Helvetica">accept_statement</FONT>s
only for its own entries.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>29</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>24 A <FONT FACE="Arial, Helvetica">return_statement</FONT>
(see <A HREF="AA-6-5.html">6.5</A>) or a <FONT FACE="Arial, Helvetica">requeue_statement</FONT>
(see <A HREF="AA-9-5-4.html">9.5.4</A>) may be used to complete the execution
of an <FONT FACE="Arial, Helvetica">accept_statement</FONT> or an <FONT FACE="Arial, Helvetica">entry_body</FONT>.
</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>29.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>An <FONT FACE="Arial, Helvetica">accept_statement</FONT>
need not have a <FONT FACE="Arial, Helvetica">handled_sequence_of_statements</FONT>
even if the corresponding entry has parameters. Equally, it can have
a <FONT FACE="Arial, Helvetica">handled_sequence_of_statements</FONT>
even if the corresponding entry has no parameters. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>29.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>A single
entry overloads a subprogram, an enumeration literal, or another single
entry if they have the same <FONT FACE="Arial, Helvetica">defining_identifier</FONT>.
Overloading is not allowed for entry family names. A single entry or
an entry of an entry family can be renamed as a procedure as explained
in <A HREF="AA-8-5-4.html">8.5.4</A>. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>30</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>25 The <FONT FACE="Arial, Helvetica">condition</FONT>
in the <FONT FACE="Arial, Helvetica">entry_barrier</FONT> may reference
anything visible except the formal parameters of the entry. This includes
the entry index (if any), the components (including discriminants) of
the protected object, the Count attribute of an entry of that protected
object, and data global to the protected unit.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>31</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>The restriction against referencing
the formal parameters within an <FONT FACE="Arial, Helvetica">entry_barrier</FONT>
ensures that all calls of the same entry see the same barrier value.
If it is necessary to look at the parameters of an entry call before
deciding whether to handle it, the <FONT FACE="Arial, Helvetica">entry_barrier</FONT>
can be ``<B>when</B> True'' and the caller can be requeued (on some private
entry) when its parameters indicate that it cannot be handled immediately.
</FONT></DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>32</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Examples of
entry declarations:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>33</FONT></DIV>
<DIV Class="Examples"><TT><B>entry</B> Read(V : <B>out</B> Item);<BR>
<B>entry</B> Seize;<BR>
<B>entry</B> Request(Level)(D : Item); <I>-- a family of entries</I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>34</FONT></DIV>
<DIV Class="Wide" Style="margin-bottom: 0.4em"> <I>Examples of accept
statements:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>35</FONT></DIV>
<DIV Class="Examples"><TT><B>accept</B> Shut_Down;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>36</FONT></DIV>
<DIV Class="Examples"><TT><B>accept</B> Read(V : <B>out</B> Item) <B>do</B><BR>
V := Local_Item;<BR>
<B>end</B> Read;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>37</FONT></DIV>
<DIV Class="Examples"><TT><B>accept</B> Request(Low)(D : Item) <B>do</B><BR>
...<BR>
<B>end</B> Request;</TT></DIV>
<H4 ALIGN=CENTER>Extensions to Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>37.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><A NAME="I3645"></A>The syntax
rule for <FONT FACE="Arial, Helvetica">entry_body</FONT> is new.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>37.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><FONT FACE="Arial, Helvetica">Accept_statement</FONT>s
can now have <FONT FACE="Arial, Helvetica">exception_handler</FONT>s.</FONT></DIV>
<HR>
<P><A HREF="AA-TOC.html">Contents</A> <A HREF="AA-0-29.html">Index</A> <A HREF="AA-9-5-1.html">Previous</A> <A HREF="AA-9-5-3.html">Next</A> <A HREF="AA-TTL.html">Legal</A></P>
</BODY>
</HTML>
|
