path: root/Modules/_multiprocessing/semaphore.c

/*
 * A type which wraps a semaphore
 *
 * semaphore.c
 *
 * Copyright (c) 2006-2008, R Oudkerk --- see COPYING.txt
 */

#include "multiprocessing.h"

enum { RECURSIVE_MUTEX, SEMAPHORE };

typedef struct {
	PyObject_HEAD
	SEM_HANDLE handle;
	long last_tid;
	int count;
	int maxvalue;
	int kind;
} SemLockObject;

#define ISMINE(o) (o->count > 0 && PyThread_get_thread_ident() == o->last_tid)


#ifdef MS_WINDOWS

/*
 * Windows definitions
 */

#define SEM_FAILED NULL

#define SEM_CLEAR_ERROR() SetLastError(0)
#define SEM_GET_LAST_ERROR() GetLastError()
#define SEM_CREATE(name, val, max) CreateSemaphore(NULL, val, max, NULL)
#define SEM_CLOSE(sem) (CloseHandle(sem) ? 0 : -1)
#define SEM_GETVALUE(sem, pval) _GetSemaphoreValue(sem, pval)
#define SEM_UNLINK(name) 0

static int
_GetSemaphoreValue(HANDLE handle, long *value)
{
	long previous;

	switch (WaitForSingleObject(handle, 0)) {
	case WAIT_OBJECT_0:
		if (!ReleaseSemaphore(handle, 1, &previous))
			return MP_STANDARD_ERROR;
		*value = previous + 1;
		return 0;
	case WAIT_TIMEOUT:
		*value = 0;
		return 0;
	default:
		return MP_STANDARD_ERROR;
	}
}

static PyObject *
semlock_acquire(SemLockObject *self, PyObject *args, PyObject *kwds)
{
	int blocking = 1;
	double timeout;
	PyObject *timeout_obj = Py_None;
	DWORD res, full_msecs, msecs, start, ticks;

	static char *kwlist[] = {"block", "timeout", NULL};

	if (!PyArg_ParseTupleAndKeywords(args, kwds, "|iO", kwlist,
					 &blocking, &timeout_obj))
		return NULL;

	/* calculate timeout */
	if (!blocking) {
		full_msecs = 0;
	} else if (timeout_obj == Py_None) {
		full_msecs = INFINITE;
	} else {
		timeout = PyFloat_AsDouble(timeout_obj);
		if (PyErr_Occurred())
			return NULL;
		timeout *= 1000.0;      /* convert to millisecs */
		if (timeout < 0.0) {
			timeout = 0.0;
		} else if (timeout >= 0.5 * INFINITE) { /* 25 days */
			PyErr_SetString(PyExc_OverflowError,
					"timeout is too large");
			return NULL;
		}
		full_msecs = (DWORD)(timeout + 0.5);
	}
	
	/* check whether we already own the lock */
	if (self->kind == RECURSIVE_MUTEX && ISMINE(self)) {
		++self->count;
		Py_RETURN_TRUE;
	}

	/* check whether we can acquire without blocking */
	if (WaitForSingleObject(self->handle, 0) == WAIT_OBJECT_0) {
		self->last_tid = GetCurrentThreadId();
		++self->count;
		Py_RETURN_TRUE;
	}
	
	msecs = full_msecs;
	start = GetTickCount();

	for ( ; ; ) {
		HANDLE handles[2] = {self->handle, sigint_event};
		
		/* do the wait */
		Py_BEGIN_ALLOW_THREADS
		ResetEvent(sigint_event);
		res = WaitForMultipleObjects(2, handles, FALSE, msecs);
		Py_END_ALLOW_THREADS
		
		/* handle result */
		if (res != WAIT_OBJECT_0 + 1)
			break;
		
		/* got SIGINT so give signal handler a chance to run */
		Sleep(1);
		
		/* if this is main thread let KeyboardInterrupt be raised */
		if (PyErr_CheckSignals())
			return NULL;
		
		/* recalculate timeout */
		if (msecs != INFINITE) {
			ticks = GetTickCount();
			if ((DWORD)(ticks - start) >= full_msecs)
				Py_RETURN_FALSE;
			msecs = full_msecs - (ticks - start);
		}
	}
	
	/* handle result */
	switch (res) {
	case WAIT_TIMEOUT:
		Py_RETURN_FALSE;
	case WAIT_OBJECT_0:
		self->last_tid = GetCurrentThreadId();
		++self->count;
		Py_RETURN_TRUE;
	case WAIT_FAILED:
		return PyErr_SetFromWindowsErr(0);
	default:
		PyErr_Format(PyExc_RuntimeError, "WaitForSingleObject() or "
			     "WaitForMultipleObjects() gave unrecognized "
			     "value %d", res);
		return NULL;
	}
}

static PyObject *
semlock_release(SemLockObject *self, PyObject *args)
{
	if (self->kind == RECURSIVE_MUTEX) {
		if (!ISMINE(self)) {
			PyErr_SetString(PyExc_AssertionError, "attempt to "
					"release recursive lock not owned "
					"by thread");
			return NULL;
		}
		if (self->count > 1) {
			--self->count;
			Py_RETURN_NONE;
		}
		assert(self->count == 1);
	}

	if (!ReleaseSemaphore(self->handle, 1, NULL)) {
		if (GetLastError() == ERROR_TOO_MANY_POSTS) {
			PyErr_SetString(PyExc_ValueError, "semaphore or lock "
					"released too many times");
			return NULL;
		} else {
			return PyErr_SetFromWindowsErr(0);
		}
	}

	--self->count;
	Py_RETURN_NONE;
}

#else /* !MS_WINDOWS */

/*
 * Unix definitions
 */

#define SEM_CLEAR_ERROR()
#define SEM_GET_LAST_ERROR() 0
#define SEM_CREATE(name, val, max) sem_open(name, O_CREAT | O_EXCL, 0600, val)
#define SEM_CLOSE(sem) sem_close(sem)
#define SEM_GETVALUE(sem, pval) sem_getvalue(sem, pval)
#define SEM_UNLINK(name) sem_unlink(name)

#if HAVE_BROKEN_SEM_UNLINK
#  define sem_unlink(name) 0
#endif

#if !HAVE_SEM_TIMEDWAIT
#  define sem_timedwait(sem,deadline) sem_timedwait_save(sem,deadline,_save)

int
sem_timedwait_save(sem_t *sem, struct timespec *deadline, PyThreadState *_save)
{
	int res;
	unsigned long delay, difference;
	struct timeval now, tvdeadline, tvdelay;

	errno = 0;
	tvdeadline.tv_sec = deadline->tv_sec;
	tvdeadline.tv_usec = deadline->tv_nsec / 1000;

	for (delay = 0 ; ; delay += 1000) {
		/* poll */
		if (sem_trywait(sem) == 0)
			return 0;
		else if (errno != EAGAIN)
			return MP_STANDARD_ERROR;

		/* get current time */
		if (gettimeofday(&now, NULL) < 0)
			return MP_STANDARD_ERROR;

		/* check for timeout */
		if (tvdeadline.tv_sec < now.tv_sec || 
		    (tvdeadline.tv_sec == now.tv_sec && 
		     tvdeadline.tv_usec <= now.tv_usec)) {
			errno = ETIMEDOUT;
			return MP_STANDARD_ERROR;
		}

		/* calculate how much time is left */
		difference = (tvdeadline.tv_sec - now.tv_sec) * 1000000 + 
			(tvdeadline.tv_usec - now.tv_usec);

		/* check delay not too long -- maximum is 20 msecs */
		if (delay > 20000)
			delay = 20000;
		if (delay > difference)
			delay = difference;

		/* sleep */
		tvdelay.tv_sec = delay / 1000000;
		tvdelay.tv_usec = delay % 1000000;
		if (select(0, NULL, NULL, NULL, &tvdelay) < 0)
			return MP_STANDARD_ERROR;

		/* check for signals */
		Py_BLOCK_THREADS 
		res = PyErr_CheckSignals();
		Py_UNBLOCK_THREADS

		if (res) {
			errno = EINTR;
			return MP_EXCEPTION_HAS_BEEN_SET;
		}
	}
}

#endif /* !HAVE_SEM_TIMEDWAIT */

static PyObject *
semlock_acquire(SemLockObject *self, PyObject *args, PyObject *kwds)
{
	int blocking = 1, res;
	double timeout;
	PyObject *timeout_obj = Py_None;
	struct timespec deadline = {0};
	struct timeval now;
	long sec, nsec;

	static char *kwlist[] = {"block", "timeout", NULL};

	if (!PyArg_ParseTupleAndKeywords(args, kwds, "|iO", kwlist,
					 &blocking, &timeout_obj))
		return NULL;

	if (self->kind == RECURSIVE_MUTEX && ISMINE(self)) {
		++self->count;
		Py_RETURN_TRUE;
	}

	if (timeout_obj != Py_None) {
		timeout = PyFloat_AsDouble(timeout_obj);
		if (PyErr_Occurred())
			return NULL;
		if (timeout < 0.0)
			timeout = 0.0;

		if (gettimeofday(&now, NULL) < 0) {
			PyErr_SetFromErrno(PyExc_OSError);
			return NULL;
		}
		sec = (long) timeout;
		nsec = (long) (1e9 * (timeout - sec) + 0.5);
		deadline.tv_sec = now.tv_sec + sec;
		deadline.tv_nsec = now.tv_usec * 1000 + nsec;
		deadline.tv_sec += (deadline.tv_nsec / 1000000000);
		deadline.tv_nsec %= 1000000000;
	}

	do {
		Py_BEGIN_ALLOW_THREADS
		if (blocking && timeout_obj == Py_None)
			res = sem_wait(self->handle);
		else if (!blocking)
			res = sem_trywait(self->handle);
		else
			res = sem_timedwait(self->handle, &deadline);
		Py_END_ALLOW_THREADS
		if (res == MP_EXCEPTION_HAS_BEEN_SET)
			break;
	} while (res < 0 && errno == EINTR && !PyErr_CheckSignals());

	if (res < 0) {
		if (errno == EAGAIN || errno == ETIMEDOUT)
			Py_RETURN_FALSE;
		else if (errno == EINTR)
			return NULL;
		else
			return PyErr_SetFromErrno(PyExc_OSError);
	}

	++self->count;
	self->last_tid = PyThread_get_thread_ident();

	Py_RETURN_TRUE;
}

static PyObject *
semlock_release(SemLockObject *self, PyObject *args)
{
	if (self->kind == RECURSIVE_MUTEX) {
		if (!ISMINE(self)) {
			PyErr_SetString(PyExc_AssertionError, "attempt to "
					"release recursive lock not owned "
					"by thread");
			return NULL;
		}
		if (self->count > 1) {
			--self->count;
			Py_RETURN_NONE;
		}
		assert(self->count == 1);
	} else {
#if HAVE_BROKEN_SEM_GETVALUE
		/* We will only check properly the maxvalue == 1 case */
		if (self->maxvalue == 1) {
			/* make sure that already locked */
			if (sem_trywait(self->handle) < 0) {
				if (errno != EAGAIN) {
					PyErr_SetFromErrno(PyExc_OSError);
					return NULL;
				}
				/* it is already locked as expected */
			} else {
				/* it was not locked so undo wait and raise  */
				if (sem_post(self->handle) < 0) {
					PyErr_SetFromErrno(PyExc_OSError);
					return NULL;
				}
				PyErr_SetString(PyExc_ValueError, "semaphore "
						"or lock released too many "
						"times");
				return NULL;
			}
		}
#else
		int sval;

		/* This check is not an absolute guarantee that the semaphore
		   does not rise above maxvalue. */
		if (sem_getvalue(self->handle, &sval) < 0) {
			return PyErr_SetFromErrno(PyExc_OSError);
		} else if (sval >= self->maxvalue) {
			PyErr_SetString(PyExc_ValueError, "semaphore or lock "
					"released too many times");
			return NULL;
		}
#endif
	}

	if (sem_post(self->handle) < 0)
		return PyErr_SetFromErrno(PyExc_OSError);

	--self->count;
	Py_RETURN_NONE;
}

#endif /* !MS_WINDOWS */

/*
 * All platforms
 */

static PyObject *
newsemlockobject(PyTypeObject *type, SEM_HANDLE handle, int kind, int maxvalue)
{
	SemLockObject *self;

	self = PyObject_New(SemLockObject, type);
	if (!self)
		return NULL;
	self->handle = handle;
	self->kind = kind;
	self->count = 0;
	self->last_tid = 0;
	self->maxvalue = maxvalue;
	return (PyObject*)self;
}

static PyObject *
semlock_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
	char buffer[256];
	SEM_HANDLE handle = SEM_FAILED;
	int kind, maxvalue, value;
	PyObject *result;
	static char *kwlist[] = {"kind", "value", "maxvalue", NULL};
	static int counter = 0;

	if (!PyArg_ParseTupleAndKeywords(args, kwds, "iii", kwlist, 
					 &kind, &value, &maxvalue))
		return NULL;

	if (kind != RECURSIVE_MUTEX && kind != SEMAPHORE) {
		PyErr_SetString(PyExc_ValueError, "unrecognized kind");
		return NULL;
	}

	PyOS_snprintf(buffer, sizeof(buffer), "/mp%d-%d", getpid(), counter++);

	SEM_CLEAR_ERROR();
	handle = SEM_CREATE(buffer, value, maxvalue);
	/* On Windows we should fail if GetLastError()==ERROR_ALREADY_EXISTS */
	if (handle == SEM_FAILED || SEM_GET_LAST_ERROR() != 0)
		goto failure;

	if (SEM_UNLINK(buffer) < 0)
		goto failure;

	result = newsemlockobject(type, handle, kind, maxvalue);
	if (!result)
		goto failure;

	return result;

  failure:
	if (handle != SEM_FAILED)
		SEM_CLOSE(handle);
	mp_SetError(NULL, MP_STANDARD_ERROR);
	return NULL;
}

static PyObject *
semlock_rebuild(PyTypeObject *type, PyObject *args)
{
	SEM_HANDLE handle;
	int kind, maxvalue;

	if (!PyArg_ParseTuple(args, F_SEM_HANDLE "ii", 
			      &handle, &kind, &maxvalue))
		return NULL;

	return newsemlockobject(type, handle, kind, maxvalue);
}

static void
semlock_dealloc(SemLockObject* self)
{
	if (self->handle != SEM_FAILED)
		SEM_CLOSE(self->handle);
	PyObject_Del(self);
}

static PyObject *
semlock_count(SemLockObject *self)
{
	return PyInt_FromLong((long)self->count);
}

static PyObject *
semlock_ismine(SemLockObject *self)
{
	/* only makes sense for a lock */
	return PyBool_FromLong(ISMINE(self));
}

static PyObject *
semlock_getvalue(SemLockObject *self)
{
#if HAVE_BROKEN_SEM_GETVALUE
	PyErr_SetNone(PyExc_NotImplementedError);
	return NULL;
#else
	int sval;
	if (SEM_GETVALUE(self->handle, &sval) < 0)
		return mp_SetError(NULL, MP_STANDARD_ERROR);
	/* some posix implementations use negative numbers to indicate 
	   the number of waiting threads */
	if (sval < 0)
		sval = 0;
	return PyInt_FromLong((long)sval);
#endif
}

static PyObject *
semlock_iszero(SemLockObject *self)
{
#if HAVE_BROKEN_SEM_GETVALUE
	if (sem_trywait(self->handle) < 0) {
		if (errno == EAGAIN)
			Py_RETURN_TRUE;
		return mp_SetError(NULL, MP_STANDARD_ERROR);
	} else {
		if (sem_post(self->handle) < 0)
			return mp_SetError(NULL, MP_STANDARD_ERROR);
		Py_RETURN_FALSE;
	}
#else
	int sval;
	if (SEM_GETVALUE(self->handle, &sval) < 0)
		return mp_SetError(NULL, MP_STANDARD_ERROR);
	return PyBool_FromLong((long)sval == 0);
#endif
}

static PyObject *
semlock_afterfork(SemLockObject *self)
{
	self->count = 0;
	Py_RETURN_NONE;
}

/*
 * Semaphore methods
 */

static PyMethodDef semlock_methods[] = {
	{"acquire", (PyCFunction)semlock_acquire, METH_VARARGS | METH_KEYWORDS,
	 "acquire the semaphore/lock"},
	{"release", (PyCFunction)semlock_release, METH_NOARGS, 
	 "release the semaphore/lock"},
	{"__enter__", (PyCFunction)semlock_acquire, METH_VARARGS,
	 "enter the semaphore/lock"},
	{"__exit__", (PyCFunction)semlock_release, METH_VARARGS, 
	 "exit the semaphore/lock"},
	{"_count", (PyCFunction)semlock_count, METH_NOARGS, 
	 "num of `acquire()`s minus num of `release()`s for this process"},
	{"_is_mine", (PyCFunction)semlock_ismine, METH_NOARGS, 
	 "whether the lock is owned by this thread"},
	{"_get_value", (PyCFunction)semlock_getvalue, METH_NOARGS, 
	 "get the value of the semaphore"}, 
	{"_is_zero", (PyCFunction)semlock_iszero, METH_NOARGS, 
	 "returns whether semaphore has value zero"}, 
	{"_rebuild", (PyCFunction)semlock_rebuild, METH_VARARGS | METH_CLASS, 
	 ""}, 
	{"_after_fork", (PyCFunction)semlock_afterfork, METH_NOARGS,
	 "rezero the net acquisition count after fork()"},
	{NULL}
};

/*
 * Member table
 */

static PyMemberDef semlock_members[] = {
	{"handle", T_SEM_HANDLE, offsetof(SemLockObject, handle), READONLY, 
	 ""},
	{"kind", T_INT, offsetof(SemLockObject, kind), READONLY, 
	 ""},
	{"maxvalue", T_INT, offsetof(SemLockObject, maxvalue), READONLY, 
	 ""},
	{NULL}
};

/*
 * Semaphore type
 */

PyTypeObject SemLockType = {
	PyVarObject_HEAD_INIT(NULL, 0)
	/* tp_name           */ "_multiprocessing.SemLock",
	/* tp_basicsize      */ sizeof(SemLockObject),
	/* tp_itemsize       */ 0,
	/* tp_dealloc        */ (destructor)semlock_dealloc,
	/* tp_print          */ 0,
	/* tp_getattr        */ 0,
	/* tp_setattr        */ 0,
	/* tp_compare        */ 0,
	/* tp_repr           */ 0,
	/* tp_as_number      */ 0,
	/* tp_as_sequence    */ 0,
	/* tp_as_mapping     */ 0,
	/* tp_hash           */ 0,
	/* tp_call           */ 0,
	/* tp_str            */ 0,
	/* tp_getattro       */ 0,
	/* tp_setattro       */ 0,
	/* tp_as_buffer      */ 0,
	/* tp_flags          */ Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
	/* tp_doc            */ "Semaphore/Mutex type",
	/* tp_traverse       */ 0,
	/* tp_clear          */ 0,
	/* tp_richcompare    */ 0,
	/* tp_weaklistoffset */ 0,
	/* tp_iter           */ 0,
	/* tp_iternext       */ 0,
	/* tp_methods        */ semlock_methods,
	/* tp_members        */ semlock_members,
	/* tp_getset         */ 0,
	/* tp_base           */ 0,
	/* tp_dict           */ 0,
	/* tp_descr_get      */ 0,
	/* tp_descr_set      */ 0,
	/* tp_dictoffset     */ 0,
	/* tp_init           */ 0,
	/* tp_alloc          */ 0,
	/* tp_new            */ semlock_new,
};