/Modules/_multiprocessing/semaphore.c

  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
 11enum { RECURSIVE_MUTEX, SEMAPHORE };
 12
 13typedef 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
 40static 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
 59static PyObject *
 60semlock_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
156static PyObject *
157semlock_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#if HAVE_BROKEN_SEM_UNLINK
201#  define sem_unlink(name) 0
202#endif
203
204#if !HAVE_SEM_TIMEDWAIT
205#  define sem_timedwait(sem,deadline) sem_timedwait_save(sem,deadline,_save)
206
207int
208sem_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
267static PyObject *
268semlock_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
335static PyObject *
336semlock_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#if 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
401static PyObject *
402newsemlockobject(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
417static PyObject *
418semlock_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%d-%d", 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
460static PyObject *
461semlock_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
473static void
474semlock_dealloc(SemLockObject* self)
475{
476	if (self->handle != SEM_FAILED)
477		SEM_CLOSE(self->handle);
478	PyObject_Del(self);
479}
480
481static PyObject *
482semlock_count(SemLockObject *self)
483{
484	return PyInt_FromLong((long)self->count);
485}
486
487static PyObject *
488semlock_ismine(SemLockObject *self)
489{
490	/* only makes sense for a lock */
491	return PyBool_FromLong(ISMINE(self));
492}
493
494static PyObject *
495semlock_getvalue(SemLockObject *self)
496{
497#if 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
512static PyObject *
513semlock_iszero(SemLockObject *self)
514{
515#if 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
533static PyObject *
534semlock_afterfork(SemLockObject *self)
535{
536	self->count = 0;
537	Py_RETURN_NONE;
538}
539
540/*
541 * Semaphore methods
542 */
543
544static 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
572static 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
586PyTypeObject 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};