[d17546]: mutex.c Maximize Restore History

Download this file

mutex.c    559 lines (481 with data), 12.9 kB

  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
/*
* mutex.c
*
* Description:
* This translation unit implements mutual exclusion (mutex) primitives.
*/
#include <errno.h>
#include "pthread.h"
#include "implement.h"
static int
_mutex_check_need_init(pthread_mutex_t *mutex)
{
int result = 0;
/*
* The following guarded test is specifically for statically
* initialised mutexes (via PTHREAD_MUTEX_INITIALIZER).
*
* Note that by not providing this synchronisation we risk
* introducing race conditions into applications which are
* correctly written.
*
* Approach
* --------
* We know that static mutexes will not be PROCESS_SHARED
* so we can serialise access to internal state using
* Win32 Critical Sections rather than Win32 Mutexes.
*
* We still have a problem in that we would like a per-mutex
* lock, but attempting to create one will again lead
* to a race condition. We are forced to use a global
* lock in this instance.
*
* If using a single global lock slows applications down too much,
* multiple global locks could be created and hashed on some random
* value associated with each mutex, the pointer perhaps. At a guess,
* a good value for the optimal number of global locks might be
* the number of processors + 1.
*
* We need to maintain the following per-mutex state independently:
* - mutex staticinit (true iff mutex is static and still
* needs to be initialised)
* - mutex valid (false iff mutex has been destroyed)
*
* For example, in this implementation a mutex initialised by
* PTHREAD_MUTEX_INITIALIZER will be 'valid' but uninitialised until
* the thread attempts to lock it. It can also be destroyed (made invalid)
* before ever being locked.
*/
EnterCriticalSection(&_pthread_mutex_test_init_lock);
/*
* We got here because staticinit tested true, possibly under race
* conditions. Check staticinit again inside the critical section
* and only initialise if the mutex is valid (not been destroyed).
* If a static mutex has been destroyed, the application can
* re-initialise it only by calling pthread_mutex_init()
* explicitly.
*/
if (mutex->staticinit && mutex->valid)
{
result = pthread_mutex_init(mutex, NULL);
}
LeaveCriticalSection(&_pthread_mutex_test_init_lock);
return(result);
}
int
pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *attr)
{
int result = 0;
if (mutex == NULL)
{
return EINVAL;
}
mutex->mutex = 0;
/*
* Assuming any race condition here is harmless.
*/
if (mutex->valid && !mutex->staticinit)
{
return EBUSY;
}
if (attr != NULL
&& *attr != NULL
&& (*attr)->pshared == PTHREAD_PROCESS_SHARED
)
{
/*
* Creating mutex that can be shared between
* processes.
*/
#if _POSIX_THREAD_PROCESS_SHARED
/*
* Not implemented yet.
*/
#error ERROR [__FILE__, line __LINE__]: Process shared mutexes are not supported yet.
mutex->mutex = CreateMutex (
NULL,
FALSE,
????);
result = (mutex->mutex == 0) ? EAGAIN : 0;
#else
result = ENOSYS;
#endif /* _POSIX_THREAD_PROCESS_SHARED */
}
else
{
if (_pthread_try_enter_critical_section != NULL
|| (attr != NULL
&& *attr != NULL
&& (*attr)->forcecs == 1)
)
{
/*
* Create a critical section.
*/
InitializeCriticalSection(&mutex->cs);
}
else
{
/*
* Create a mutex that can only be used within the
* current process
*/
mutex->mutex = CreateMutex (NULL,
FALSE,
NULL);
result = (mutex->mutex == 0) ? EAGAIN : 0;
}
}
if (result == 0)
{
mutex->staticinit = 0;
/* Mark as valid. */
mutex->valid = 1;
}
return(result);
}
int
pthread_mutex_destroy(pthread_mutex_t *mutex)
{
int result = 0;
if (mutex == NULL)
{
return EINVAL;
}
/*
* Check to see if we have something to delete.
*/
if (!mutex->staticinit)
{
if (mutex->mutex == 0)
{
DeleteCriticalSection(&mutex->cs);
}
else
{
result = (CloseHandle (mutex->mutex) ? 0 : EINVAL);
}
}
if (result == 0)
{
mutex->mutex = 0;
/* Mark as invalid. */
mutex->valid = 0;
}
return(result);
}
int
pthread_mutexattr_init (pthread_mutexattr_t * attr)
/*
* ------------------------------------------------------
* DOCPUBLIC
* Initializes a mutex attributes object with default
* attributes.
*
* PARAMETERS
* attr
* pointer to an instance of pthread_mutexattr_t
*
*
* DESCRIPTION
* Initializes a mutex attributes object with default
* attributes.
*
* NOTES:
* 1) Used to define mutex types
*
* RESULTS
* 0 successfully initialized attr,
* ENOMEM insufficient memory for attr.
*
* ------------------------------------------------------
*/
{
pthread_mutexattr_t attr_result;
int result = 0;
attr_result = (pthread_mutexattr_t) calloc (1, sizeof (*attr_result));
result = (attr_result == NULL)
? ENOMEM
: 0;
*attr = attr_result;
return (result);
} /* pthread_mutexattr_init */
int
pthread_mutexattr_destroy (pthread_mutexattr_t * attr)
/*
* ------------------------------------------------------
* DOCPUBLIC
* Destroys a mutex attributes object. The object can
* no longer be used.
*
* PARAMETERS
* attr
* pointer to an instance of pthread_mutexattr_t
*
*
* DESCRIPTION
* Destroys a mutex attributes object. The object can
* no longer be used.
*
* NOTES:
* 1) Does not affect mutexes created using 'attr'
*
* RESULTS
* 0 successfully released attr,
* EINVAL 'attr' is invalid.
*
* ------------------------------------------------------
*/
{
int result = 0;
if (attr == NULL || *attr == NULL)
{
result = EINVAL;
}
else
{
free (*attr);
*attr = NULL;
result = 0;
}
return (result);
} /* pthread_mutexattr_destroy */
int
pthread_mutexattr_setforcecs_np(pthread_mutexattr_t *attr,
int forcecs)
{
if (attr == NULL || *attr == NULL)
{
/* This is disallowed. */
return EINVAL;
}
(*attr)->forcecs = forcecs;
return 0;
}
int
pthread_mutexattr_getpshared (const pthread_mutexattr_t * attr,
int *pshared)
/*
* ------------------------------------------------------
* DOCPUBLIC
* Determine whether mutexes created with 'attr' can be
* shared between processes.
*
* PARAMETERS
* attr
* pointer to an instance of pthread_mutexattr_t
*
* pshared
* will be set to one of:
*
* PTHREAD_PROCESS_SHARED
* May be shared if in shared memory
*
* PTHREAD_PROCESS_PRIVATE
* Cannot be shared.
*
*
* DESCRIPTION
* Mutexes creatd with 'attr' can be shared between
* processes if pthread_mutex_t variable is allocated
* in memory shared by these processes.
* NOTES:
* 1) pshared mutexes MUST be allocated in shared
* memory.
* 2) The following macro is defined if shared mutexes
* are supported:
* _POSIX_THREAD_PROCESS_SHARED
*
* RESULTS
* 0 successfully retrieved attribute,
* EINVAL 'attr' is invalid,
*
* ------------------------------------------------------
*/
{
int result;
if ((attr != NULL && *attr != NULL) &&
(pshared != NULL))
{
*pshared = (*attr)->pshared;
result = 0;
}
else
{
*pshared = PTHREAD_PROCESS_PRIVATE;
result = EINVAL;
}
return (result);
} /* pthread_mutexattr_getpshared */
int
pthread_mutexattr_setpshared (pthread_mutexattr_t * attr,
int pshared)
/*
* ------------------------------------------------------
* DOCPUBLIC
* Mutexes created with 'attr' can be shared between
* processes if pthread_mutex_t variable is allocated
* in memory shared by these processes.
*
* PARAMETERS
* attr
* pointer to an instance of pthread_mutexattr_t
*
* pshared
* must be one of:
*
* PTHREAD_PROCESS_SHARED
* May be shared if in shared memory
*
* PTHREAD_PROCESS_PRIVATE
* Cannot be shared.
*
* DESCRIPTION
* Mutexes creatd with 'attr' can be shared between
* processes if pthread_mutex_t variable is allocated
* in memory shared by these processes.
*
* NOTES:
* 1) pshared mutexes MUST be allocated in shared
* memory.
*
* 2) The following macro is defined if shared mutexes
* are supported:
* _POSIX_THREAD_PROCESS_SHARED
*
* RESULTS
* 0 successfully set attribute,
* EINVAL 'attr' or pshared is invalid,
* ENOSYS PTHREAD_PROCESS_SHARED not supported,
*
* ------------------------------------------------------
*/
{
int result;
if ((attr != NULL && *attr != NULL) &&
((pshared == PTHREAD_PROCESS_SHARED) ||
(pshared == PTHREAD_PROCESS_PRIVATE)))
{
if (pshared == PTHREAD_PROCESS_SHARED)
{
#if !defined( _POSIX_THREAD_PROCESS_SHARED )
result = ENOSYS;
pshared = PTHREAD_PROCESS_PRIVATE;
#else
result = 0;
#endif /* _POSIX_THREAD_PROCESS_SHARED */
}
else
{
result = 0;
}
(*attr)->pshared = pshared;
}
else
{
result = EINVAL;
}
return (result);
} /* pthread_mutexattr_setpshared */
int
pthread_mutex_lock(pthread_mutex_t *mutex)
{
int result = 0;
/*
* We do a quick check to see if we need to do more work
* to initialise a static mutex. We check 'staticinit'
* again inside the guarded section of _mutex_check_need_init()
* to avoid race conditions.
*/
if (mutex->staticinit)
{
result = _mutex_check_need_init(mutex);
}
if (result == 0)
{
if (mutex->mutex == 0)
{
EnterCriticalSection(&mutex->cs);
}
else
{
result = (WaitForSingleObject(mutex->mutex, INFINITE)
== WAIT_OBJECT_0)
? 0
: EINVAL;
}
}
return(result);
}
int
pthread_mutex_unlock(pthread_mutex_t *mutex)
{
int result = 0;
/*
* If the thread calling us holds the mutex then there is no
* race condition. If another thread holds the
* lock then we shouldn't be in here.
*/
if (!mutex->staticinit && mutex->valid)
{
if (mutex->mutex == 0)
{
LeaveCriticalSection(&mutex->cs);
}
else
{
result = (ReleaseMutex (mutex->mutex) ? 0 : EINVAL);
}
}
else
{
result = EINVAL;
}
return(result);
}
int
pthread_mutex_trylock(pthread_mutex_t *mutex)
{
int result = 0;
if (mutex->mutex == 0 && _pthread_try_enter_critical_section == NULL)
{
/* TryEnterCriticalSection does not exist in the OS; return ENOSYS. */
return ENOSYS;
}
if (mutex == NULL)
{
return EINVAL;
}
/*
* We do a quick check to see if we need to do more work
* to initialise a static mutex. We check 'staticinit'
* again inside the guarded section of _mutex_check_need_init()
* to avoid race conditions.
*/
if (mutex->staticinit)
{
result = _mutex_check_need_init(mutex);
}
if (result == 0)
{
if (mutex->mutex == 0)
{
if ((*_pthread_try_enter_critical_section)(&mutex->cs) != TRUE)
{
result = EBUSY;
}
}
else
{
DWORD status;
status = WaitForSingleObject (mutex->mutex, 0);
if (status != WAIT_OBJECT_0)
{
result = ((status == WAIT_TIMEOUT)
? EBUSY
: EINVAL);
}
}
}
return(result);
}