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1 /*
2 * A type which wraps a semaphore
3 *
4 * semaphore.c
5 *
6 * Copyright (c) 2006-2008, R Oudkerk --- see COPYING.txt
7 */
8
9 #include "multiprocessing.h"
10
11 enum { RECURSIVE_MUTEX, SEMAPHORE };
12
13 typedef struct {
14 PyObject_HEAD
15 SEM_HANDLE handle;
16 long last_tid;
17 int count;
18 int maxvalue;
19 int kind;
20 } SemLockObject;
21
22 #define ISMINE(o) (o->count > 0 && PyThread_get_thread_ident() == o->last_tid)
23
24
25 #ifdef MS_WINDOWS
26
27 /*
28 * Windows definitions
29 */
30
31 #define SEM_FAILED NULL
32
33 #define SEM_CLEAR_ERROR() SetLastError(0)
34 #define SEM_GET_LAST_ERROR() GetLastError()
35 #define SEM_CREATE(name, val, max) CreateSemaphore(NULL, val, max, NULL)
36 #define SEM_CLOSE(sem) (CloseHandle(sem) ? 0 : -1)
37 #define SEM_GETVALUE(sem, pval) _GetSemaphoreValue(sem, pval)
38 #define SEM_UNLINK(name) 0
39
40 static int
41 _GetSemaphoreValue(HANDLE handle, long *value)
42 {
43 long previous;
44
45 switch (WaitForSingleObject(handle, 0)) {
46 case WAIT_OBJECT_0:
47 if (!ReleaseSemaphore(handle, 1, &previous))
48 return MP_STANDARD_ERROR;
49 *value = previous + 1;
50 return 0;
51 case WAIT_TIMEOUT:
52 *value = 0;
53 return 0;
54 default:
55 return MP_STANDARD_ERROR;
56 }
57 }
58
59 static PyObject *
60 semlock_acquire(SemLockObject *self, PyObject *args, PyObject *kwds)
61 {
62 int blocking = 1;
63 double timeout;
64 PyObject *timeout_obj = Py_None;
65 DWORD res, full_msecs, msecs, start, ticks;
66
67 static char *kwlist[] = {"block", "timeout", NULL};
68
69 if (!PyArg_ParseTupleAndKeywords(args, kwds, "|iO", kwlist,
70 &blocking, &timeout_obj))
71 return NULL;
72
73 /* calculate timeout */
74 if (!blocking) {
75 full_msecs = 0;
76 } else if (timeout_obj == Py_None) {
77 full_msecs = INFINITE;
78 } else {
79 timeout = PyFloat_AsDouble(timeout_obj);
80 if (PyErr_Occurred())
81 return NULL;
82 timeout *= 1000.0; /* convert to millisecs */
83 if (timeout < 0.0) {
84 timeout = 0.0;
85 } else if (timeout >= 0.5 * INFINITE) { /* 25 days */
86 PyErr_SetString(PyExc_OverflowError,
87 "timeout is too large");
88 return NULL;
89 }
90 full_msecs = (DWORD)(timeout + 0.5);
91 }
92
93 /* check whether we already own the lock */
94 if (self->kind == RECURSIVE_MUTEX && ISMINE(self)) {
95 ++self->count;
96 Py_RETURN_TRUE;
97 }
98
99 /* check whether we can acquire without blocking */
100 if (WaitForSingleObject(self->handle, 0) == WAIT_OBJECT_0) {
101 self->last_tid = GetCurrentThreadId();
102 ++self->count;
103 Py_RETURN_TRUE;
104 }
105
106 msecs = full_msecs;
107 start = GetTickCount();
108
109 for ( ; ; ) {
110 HANDLE handles[2] = {self->handle, sigint_event};
111
112 /* do the wait */
113 Py_BEGIN_ALLOW_THREADS
114 ResetEvent(sigint_event);
115 res = WaitForMultipleObjects(2, handles, FALSE, msecs);
116 Py_END_ALLOW_THREADS
117
118 /* handle result */
119 if (res != WAIT_OBJECT_0 + 1)
120 break;
121
122 /* got SIGINT so give signal handler a chance to run */
123 Sleep(1);
124
125 /* if this is main thread let KeyboardInterrupt be raised */
126 if (PyErr_CheckSignals())
127 return NULL;
128
129 /* recalculate timeout */
130 if (msecs != INFINITE) {
131 ticks = GetTickCount();
132 if ((DWORD)(ticks - start) >= full_msecs)
133 Py_RETURN_FALSE;
134 msecs = full_msecs - (ticks - start);
135 }
136 }
137
138 /* handle result */
139 switch (res) {
140 case WAIT_TIMEOUT:
141 Py_RETURN_FALSE;
142 case WAIT_OBJECT_0:
143 self->last_tid = GetCurrentThreadId();
144 ++self->count;
145 Py_RETURN_TRUE;
146 case WAIT_FAILED:
147 return PyErr_SetFromWindowsErr(0);
148 default:
149 PyErr_Format(PyExc_RuntimeError, "WaitForSingleObject() or "
150 "WaitForMultipleObjects() gave unrecognized "
151 "value %d", res);
152 return NULL;
153 }
154 }
155
156 static PyObject *
157 semlock_release(SemLockObject *self, PyObject *args)
158 {
159 if (self->kind == RECURSIVE_MUTEX) {
160 if (!ISMINE(self)) {
161 PyErr_SetString(PyExc_AssertionError, "attempt to "
162 "release recursive lock not owned "
163 "by thread");
164 return NULL;
165 }
166 if (self->count > 1) {
167 --self->count;
168 Py_RETURN_NONE;
169 }
170 assert(self->count == 1);
171 }
172
173 if (!ReleaseSemaphore(self->handle, 1, NULL)) {
174 if (GetLastError() == ERROR_TOO_MANY_POSTS) {
175 PyErr_SetString(PyExc_ValueError, "semaphore or lock "
176 "released too many times");
177 return NULL;
178 } else {
179 return PyErr_SetFromWindowsErr(0);
180 }
181 }
182
183 --self->count;
184 Py_RETURN_NONE;
185 }
186
187 #else /* !MS_WINDOWS */
188
189 /*
190 * Unix definitions
191 */
192
193 #define SEM_CLEAR_ERROR()
194 #define SEM_GET_LAST_ERROR() 0
195 #define SEM_CREATE(name, val, max) sem_open(name, O_CREAT | O_EXCL, 0600, val)
196 #define SEM_CLOSE(sem) sem_close(sem)
197 #define SEM_GETVALUE(sem, pval) sem_getvalue(sem, pval)
198 #define SEM_UNLINK(name) sem_unlink(name)
199
200 #ifndef HAVE_SEM_UNLINK
201 # define sem_unlink(name) 0
202 #endif
203
204 #ifndef HAVE_SEM_TIMEDWAIT
205 # define sem_timedwait(sem,deadline) sem_timedwait_save(sem,deadline,_save)
206
207 int
208 sem_timedwait_save(sem_t *sem, struct timespec *deadline, PyThreadState *_save)
209 {
210 int res;
211 unsigned long delay, difference;
212 struct timeval now, tvdeadline, tvdelay;
213
214 errno = 0;
215 tvdeadline.tv_sec = deadline->tv_sec;
216 tvdeadline.tv_usec = deadline->tv_nsec / 1000;
217
218 for (delay = 0 ; ; delay += 1000) {
219 /* poll */
220 if (sem_trywait(sem) == 0)
221 return 0;
222 else if (errno != EAGAIN)
223 return MP_STANDARD_ERROR;
224
225 /* get current time */
226 if (gettimeofday(&now, NULL) < 0)
227 return MP_STANDARD_ERROR;
228
229 /* check for timeout */
230 if (tvdeadline.tv_sec < now.tv_sec ||
231 (tvdeadline.tv_sec == now.tv_sec &&
232 tvdeadline.tv_usec <= now.tv_usec)) {
233 errno = ETIMEDOUT;
234 return MP_STANDARD_ERROR;
235 }
236
237 /* calculate how much time is left */
238 difference = (tvdeadline.tv_sec - now.tv_sec) * 1000000 +
239 (tvdeadline.tv_usec - now.tv_usec);
240
241 /* check delay not too long -- maximum is 20 msecs */
242 if (delay > 20000)
243 delay = 20000;
244 if (delay > difference)
245 delay = difference;
246
247 /* sleep */
248 tvdelay.tv_sec = delay / 1000000;
249 tvdelay.tv_usec = delay % 1000000;
250 if (select(0, NULL, NULL, NULL, &tvdelay) < 0)
251 return MP_STANDARD_ERROR;
252
253 /* check for signals */
254 Py_BLOCK_THREADS
255 res = PyErr_CheckSignals();
256 Py_UNBLOCK_THREADS
257
258 if (res) {
259 errno = EINTR;
260 return MP_EXCEPTION_HAS_BEEN_SET;
261 }
262 }
263 }
264
265 #endif /* !HAVE_SEM_TIMEDWAIT */
266
267 static PyObject *
268 semlock_acquire(SemLockObject *self, PyObject *args, PyObject *kwds)
269 {
270 int blocking = 1, res;
271 double timeout;
272 PyObject *timeout_obj = Py_None;
273 struct timespec deadline = {0};
274 struct timeval now;
275 long sec, nsec;
276
277 static char *kwlist[] = {"block", "timeout", NULL};
278
279 if (!PyArg_ParseTupleAndKeywords(args, kwds, "|iO", kwlist,
280 &blocking, &timeout_obj))
281 return NULL;
282
283 if (self->kind == RECURSIVE_MUTEX && ISMINE(self)) {
284 ++self->count;
285 Py_RETURN_TRUE;
286 }
287
288 if (timeout_obj != Py_None) {
289 timeout = PyFloat_AsDouble(timeout_obj);
290 if (PyErr_Occurred())
291 return NULL;
292 if (timeout < 0.0)
293 timeout = 0.0;
294
295 if (gettimeofday(&now, NULL) < 0) {
296 PyErr_SetFromErrno(PyExc_OSError);
297 return NULL;
298 }
299 sec = (long) timeout;
300 nsec = (long) (1e9 * (timeout - sec) + 0.5);
301 deadline.tv_sec = now.tv_sec + sec;
302 deadline.tv_nsec = now.tv_usec * 1000 + nsec;
303 deadline.tv_sec += (deadline.tv_nsec / 1000000000);
304 deadline.tv_nsec %= 1000000000;
305 }
306
307 do {
308 Py_BEGIN_ALLOW_THREADS
309 if (blocking && timeout_obj == Py_None)
310 res = sem_wait(self->handle);
311 else if (!blocking)
312 res = sem_trywait(self->handle);
313 else
314 res = sem_timedwait(self->handle, &deadline);
315 Py_END_ALLOW_THREADS
316 if (res == MP_EXCEPTION_HAS_BEEN_SET)
317 break;
318 } while (res < 0 && errno == EINTR && !PyErr_CheckSignals());
319
320 if (res < 0) {
321 if (errno == EAGAIN || errno == ETIMEDOUT)
322 Py_RETURN_FALSE;
323 else if (errno == EINTR)
324 return NULL;
325 else
326 return PyErr_SetFromErrno(PyExc_OSError);
327 }
328
329 ++self->count;
330 self->last_tid = PyThread_get_thread_ident();
331
332 Py_RETURN_TRUE;
333 }
334
335 static PyObject *
336 semlock_release(SemLockObject *self, PyObject *args)
337 {
338 if (self->kind == RECURSIVE_MUTEX) {
339 if (!ISMINE(self)) {
340 PyErr_SetString(PyExc_AssertionError, "attempt to "
341 "release recursive lock not owned "
342 "by thread");
343 return NULL;
344 }
345 if (self->count > 1) {
346 --self->count;
347 Py_RETURN_NONE;
348 }
349 assert(self->count == 1);
350 } else {
351 #ifdef HAVE_BROKEN_SEM_GETVALUE
352 /* We will only check properly the maxvalue == 1 case */
353 if (self->maxvalue == 1) {
354 /* make sure that already locked */
355 if (sem_trywait(self->handle) < 0) {
356 if (errno != EAGAIN) {
357 PyErr_SetFromErrno(PyExc_OSError);
358 return NULL;
359 }
360 /* it is already locked as expected */
361 } else {
362 /* it was not locked so undo wait and raise */
363 if (sem_post(self->handle) < 0) {
364 PyErr_SetFromErrno(PyExc_OSError);
365 return NULL;
366 }
367 PyErr_SetString(PyExc_ValueError, "semaphore "
368 "or lock released too many "
369 "times");
370 return NULL;
371 }
372 }
373 #else
374 int sval;
375
376 /* This check is not an absolute guarantee that the semaphore
377 does not rise above maxvalue. */
378 if (sem_getvalue(self->handle, &sval) < 0) {
379 return PyErr_SetFromErrno(PyExc_OSError);
380 } else if (sval >= self->maxvalue) {
381 PyErr_SetString(PyExc_ValueError, "semaphore or lock "
382 "released too many times");
383 return NULL;
384 }
385 #endif
386 }
387
388 if (sem_post(self->handle) < 0)
389 return PyErr_SetFromErrno(PyExc_OSError);
390
391 --self->count;
392 Py_RETURN_NONE;
393 }
394
395 #endif /* !MS_WINDOWS */
396
397 /*
398 * All platforms
399 */
400
401 static PyObject *
402 newsemlockobject(PyTypeObject *type, SEM_HANDLE handle, int kind, int maxvalue)
403 {
404 SemLockObject *self;
405
406 self = PyObject_New(SemLockObject, type);
407 if (!self)
408 return NULL;
409 self->handle = handle;
410 self->kind = kind;
411 self->count = 0;
412 self->last_tid = 0;
413 self->maxvalue = maxvalue;
414 return (PyObject*)self;
415 }
416
417 static PyObject *
418 semlock_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
419 {
420 char buffer[256];
421 SEM_HANDLE handle = SEM_FAILED;
422 int kind, maxvalue, value;
423 PyObject *result;
424 static char *kwlist[] = {"kind", "value", "maxvalue", NULL};
425 static int counter = 0;
426
427 if (!PyArg_ParseTupleAndKeywords(args, kwds, "iii", kwlist,
428 &kind, &value, &maxvalue))
429 return NULL;
430
431 if (kind != RECURSIVE_MUTEX && kind != SEMAPHORE) {
432 PyErr_SetString(PyExc_ValueError, "unrecognized kind");
433 return NULL;
434 }
435
436 PyOS_snprintf(buffer, sizeof(buffer), "/mp%ld-%d", (long)getpid(), counter++);
437
438 SEM_CLEAR_ERROR();
439 handle = SEM_CREATE(buffer, value, maxvalue);
440 /* On Windows we should fail if GetLastError()==ERROR_ALREADY_EXISTS */
441 if (handle == SEM_FAILED || SEM_GET_LAST_ERROR() != 0)
442 goto failure;
443
444 if (SEM_UNLINK(buffer) < 0)
445 goto failure;
446
447 result = newsemlockobject(type, handle, kind, maxvalue);
448 if (!result)
449 goto failure;
450
451 return result;
452
453 failure:
454 if (handle != SEM_FAILED)
455 SEM_CLOSE(handle);
456 mp_SetError(NULL, MP_STANDARD_ERROR);
457 return NULL;
458 }
459
460 static PyObject *
461 semlock_rebuild(PyTypeObject *type, PyObject *args)
462 {
463 SEM_HANDLE handle;
464 int kind, maxvalue;
465
466 if (!PyArg_ParseTuple(args, F_SEM_HANDLE "ii",
467 &handle, &kind, &maxvalue))
468 return NULL;
469
470 return newsemlockobject(type, handle, kind, maxvalue);
471 }
472
473 static void
474 semlock_dealloc(SemLockObject* self)
475 {
476 if (self->handle != SEM_FAILED)
477 SEM_CLOSE(self->handle);
478 PyObject_Del(self);
479 }
480
481 static PyObject *
482 semlock_count(SemLockObject *self)
483 {
484 return PyInt_FromLong((long)self->count);
485 }
486
487 static PyObject *
488 semlock_ismine(SemLockObject *self)
489 {
490 /* only makes sense for a lock */
491 return PyBool_FromLong(ISMINE(self));
492 }
493
494 static PyObject *
495 semlock_getvalue(SemLockObject *self)
496 {
497 #ifdef HAVE_BROKEN_SEM_GETVALUE
498 PyErr_SetNone(PyExc_NotImplementedError);
499 return NULL;
500 #else
501 int sval;
502 if (SEM_GETVALUE(self->handle, &sval) < 0)
503 return mp_SetError(NULL, MP_STANDARD_ERROR);
504 /* some posix implementations use negative numbers to indicate
505 the number of waiting threads */
506 if (sval < 0)
507 sval = 0;
508 return PyInt_FromLong((long)sval);
509 #endif
510 }
511
512 static PyObject *
513 semlock_iszero(SemLockObject *self)
514 {
515 #ifdef HAVE_BROKEN_SEM_GETVALUE
516 if (sem_trywait(self->handle) < 0) {
517 if (errno == EAGAIN)
518 Py_RETURN_TRUE;
519 return mp_SetError(NULL, MP_STANDARD_ERROR);
520 } else {
521 if (sem_post(self->handle) < 0)
522 return mp_SetError(NULL, MP_STANDARD_ERROR);
523 Py_RETURN_FALSE;
524 }
525 #else
526 int sval;
527 if (SEM_GETVALUE(self->handle, &sval) < 0)
528 return mp_SetError(NULL, MP_STANDARD_ERROR);
529 return PyBool_FromLong((long)sval == 0);
530 #endif
531 }
532
533 static PyObject *
534 semlock_afterfork(SemLockObject *self)
535 {
536 self->count = 0;
537 Py_RETURN_NONE;
538 }
539
540 /*
541 * Semaphore methods
542 */
543
544 static PyMethodDef semlock_methods[] = {
545 {"acquire", (PyCFunction)semlock_acquire, METH_VARARGS | METH_KEYWORDS,
546 "acquire the semaphore/lock"},
547 {"release", (PyCFunction)semlock_release, METH_NOARGS,
548 "release the semaphore/lock"},
549 {"__enter__", (PyCFunction)semlock_acquire, METH_VARARGS | METH_KEYWORDS,
550 "enter the semaphore/lock"},
551 {"__exit__", (PyCFunction)semlock_release, METH_VARARGS,
552 "exit the semaphore/lock"},
553 {"_count", (PyCFunction)semlock_count, METH_NOARGS,
554 "num of `acquire()`s minus num of `release()`s for this process"},
555 {"_is_mine", (PyCFunction)semlock_ismine, METH_NOARGS,
556 "whether the lock is owned by this thread"},
557 {"_get_value", (PyCFunction)semlock_getvalue, METH_NOARGS,
558 "get the value of the semaphore"},
559 {"_is_zero", (PyCFunction)semlock_iszero, METH_NOARGS,
560 "returns whether semaphore has value zero"},
561 {"_rebuild", (PyCFunction)semlock_rebuild, METH_VARARGS | METH_CLASS,
562 ""},
563 {"_after_fork", (PyCFunction)semlock_afterfork, METH_NOARGS,
564 "rezero the net acquisition count after fork()"},
565 {NULL}
566 };
567
568 /*
569 * Member table
570 */
571
572 static PyMemberDef semlock_members[] = {
573 {"handle", T_SEM_HANDLE, offsetof(SemLockObject, handle), READONLY,
574 ""},
575 {"kind", T_INT, offsetof(SemLockObject, kind), READONLY,
576 ""},
577 {"maxvalue", T_INT, offsetof(SemLockObject, maxvalue), READONLY,
578 ""},
579 {NULL}
580 };
581
582 /*
583 * Semaphore type
584 */
585
586 PyTypeObject SemLockType = {
587 PyVarObject_HEAD_INIT(NULL, 0)
588 /* tp_name */ "_multiprocessing.SemLock",
589 /* tp_basicsize */ sizeof(SemLockObject),
590 /* tp_itemsize */ 0,
591 /* tp_dealloc */ (destructor)semlock_dealloc,
592 /* tp_print */ 0,
593 /* tp_getattr */ 0,
594 /* tp_setattr */ 0,
595 /* tp_compare */ 0,
596 /* tp_repr */ 0,
597 /* tp_as_number */ 0,
598 /* tp_as_sequence */ 0,
599 /* tp_as_mapping */ 0,
600 /* tp_hash */ 0,
601 /* tp_call */ 0,
602 /* tp_str */ 0,
603 /* tp_getattro */ 0,
604 /* tp_setattro */ 0,
605 /* tp_as_buffer */ 0,
606 /* tp_flags */ Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
607 /* tp_doc */ "Semaphore/Mutex type",
608 /* tp_traverse */ 0,
609 /* tp_clear */ 0,
610 /* tp_richcompare */ 0,
611 /* tp_weaklistoffset */ 0,
612 /* tp_iter */ 0,
613 /* tp_iternext */ 0,
614 /* tp_methods */ semlock_methods,
615 /* tp_members */ semlock_members,
616 /* tp_getset */ 0,
617 /* tp_base */ 0,
618 /* tp_dict */ 0,
619 /* tp_descr_get */ 0,
620 /* tp_descr_set */ 0,
621 /* tp_dictoffset */ 0,
622 /* tp_init */ 0,
623 /* tp_alloc */ 0,
624 /* tp_new */ semlock_new,
625 };