cpython/Modules/_multiprocessing/semaphore.c at pythoncapi · pythoncapi/cpython · GitHub

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* A type which wraps a semaphore

* semaphore.c

* Licensed to PSF under a Contributor Agreement.

#include "multiprocessing.h"

enum { RECURSIVE_MUTEX, SEMAPHORE };

typedef struct {

PyObject_HEAD

SEM_HANDLE handle;

unsigned long last_tid;

int count;

int maxvalue;

int kind;

char *name;

} 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 (WaitForSingleObjectEx(handle, 0, FALSE)) {

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, nhandles;

HANDLE handles[2], sigint_event;

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 releasing the GIL and blocking */

if (WaitForSingleObjectEx(self->handle, 0, FALSE) == WAIT_OBJECT_0) {

self->last_tid = GetCurrentThreadId();

++self->count;

Py_RETURN_TRUE;

}

/* prepare list of handles */

nhandles = 0;

handles[nhandles++] = self->handle;

if (_PyOS_IsMainThread()) {

sigint_event = _PyOS_SigintEvent();

assert(sigint_event != NULL);

handles[nhandles++] = sigint_event;

}

else {

sigint_event = NULL;

}

/* do the wait */

Py_BEGIN_ALLOW_THREADS

if (sigint_event != NULL)

ResetEvent(sigint_event);

res = WaitForMultipleObjectsEx(nhandles, handles, FALSE, full_msecs, FALSE);

Py_END_ALLOW_THREADS

/* handle result */

switch (res) {

case WAIT_TIMEOUT:

Py_RETURN_FALSE;

case WAIT_OBJECT_0 + 0:

self->last_tid = GetCurrentThreadId();

++self->count;

Py_RETURN_TRUE;

case WAIT_OBJECT_0 + 1:

errno = EINTR;

return PyErr_SetFromErrno(PyExc_OSError);

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)

/* OS X 10.4 defines SEM_FAILED as -1 instead of (sem_t *)-1; this gives

compiler warnings, and (potentially) undefined behaviour. */

#ifdef __APPLE__

# undef SEM_FAILED

# define SEM_FAILED ((sem_t *)-1)

#endif

#ifndef HAVE_SEM_UNLINK

# define sem_unlink(name) 0

#endif

#ifndef HAVE_SEM_TIMEDWAIT

# define sem_timedwait(sem,deadline) sem_timedwait_save(sem,deadline,_save)

static 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, err = 0;

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;

}

/* Check whether we can acquire without releasing the GIL and blocking */

do {

res = sem_trywait(self->handle);

err = errno;

} while (res < 0 && errno == EINTR && !PyErr_CheckSignals());

errno = err;

if (res < 0 && errno == EAGAIN && blocking) {

/* Couldn't acquire immediately, need to block */

do {

Py_BEGIN_ALLOW_THREADS

if (timeout_obj == Py_None) {

res = sem_wait(self->handle);

}

else {

res = sem_timedwait(self->handle, &deadline);

}

Py_END_ALLOW_THREADS

err = errno;

if (res == MP_EXCEPTION_HAS_BEEN_SET)

break;

} while (res < 0 && errno == EINTR && !PyErr_CheckSignals());

}

if (res < 0) {

errno = err;

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 {

#ifdef 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,

char *name)

{

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;

self->name = name;

return (PyObject*)self;

}

static PyObject *

semlock_new(PyTypeObject *type, PyObject *args, PyObject *kwds)

{

SEM_HANDLE handle = SEM_FAILED;

int kind, maxvalue, value, unlink;

PyObject *result;

char *name, *name_copy = NULL;

static char *kwlist[] = {"kind", "value", "maxvalue", "name", "unlink",

NULL};

if (!PyArg_ParseTupleAndKeywords(args, kwds, "iiisi", kwlist,

&kind, &value, &maxvalue, &name, &unlink))

return NULL;

if (kind != RECURSIVE_MUTEX && kind != SEMAPHORE) {

PyErr_SetString(PyExc_ValueError, "unrecognized kind");

return NULL;

}

if (!unlink) {

name_copy = PyMem_Malloc(strlen(name) + 1);

if (name_copy == NULL)

goto failure;

strcpy(name_copy, name);

}

SEM_CLEAR_ERROR();

handle = SEM_CREATE(name, value, maxvalue);

/* On Windows we should fail if GetLastError()==ERROR_ALREADY_EXISTS */

if (handle == SEM_FAILED || SEM_GET_LAST_ERROR() != 0)

goto failure;

if (unlink && SEM_UNLINK(name) < 0)

goto failure;

result = newsemlockobject(type, handle, kind, maxvalue, name_copy);

if (!result)

goto failure;

return result;

failure:

if (handle != SEM_FAILED)

SEM_CLOSE(handle);

PyMem_Free(name_copy);

_PyMp_SetError(NULL, MP_STANDARD_ERROR);

return NULL;

}

static PyObject *

semlock_rebuild(PyTypeObject *type, PyObject *args)

{

SEM_HANDLE handle;

int kind, maxvalue;

char *name, *name_copy = NULL;

if (!PyArg_ParseTuple(args, F_SEM_HANDLE "iiz",

&handle, &kind, &maxvalue, &name))

return NULL;

if (name != NULL) {

name_copy = PyMem_Malloc(strlen(name) + 1);

if (name_copy == NULL)

return PyErr_NoMemory();

strcpy(name_copy, name);

}

#ifndef MS_WINDOWS

if (name != NULL) {

handle = sem_open(name, 0);

if (handle == SEM_FAILED) {

PyMem_Free(name_copy);

return PyErr_SetFromErrno(PyExc_OSError);

}

#endif

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

}

static void

semlock_dealloc(SemLockObject* self)

{

if (self->handle != SEM_FAILED)

SEM_CLOSE(self->handle);

PyMem_Free(self->name);

PyObject_Del(self);

}

static PyObject *

semlock_count(SemLockObject *self, PyObject *Py_UNUSED(ignored))

{

return PyLong_FromLong((long)self->count);

}

static PyObject *

semlock_ismine(SemLockObject *self, PyObject *Py_UNUSED(ignored))

{

/* only makes sense for a lock */

return PyBool_FromLong(ISMINE(self));

}

static PyObject *

semlock_getvalue(SemLockObject *self, PyObject *Py_UNUSED(ignored))

{

#ifdef HAVE_BROKEN_SEM_GETVALUE

PyErr_SetNone(PyExc_NotImplementedError);

return NULL;

#else

int sval;

if (SEM_GETVALUE(self->handle, &sval) < 0)

return _PyMp_SetError(NULL, MP_STANDARD_ERROR);

/* some posix implementations use negative numbers to indicate

the number of waiting threads */

if (sval < 0)

sval = 0;

return PyLong_FromLong((long)sval);

#endif

}

static PyObject *

semlock_iszero(SemLockObject *self, PyObject *Py_UNUSED(ignored))

{

#ifdef HAVE_BROKEN_SEM_GETVALUE

if (sem_trywait(self->handle) < 0) {

if (errno == EAGAIN)

Py_RETURN_TRUE;

return _PyMp_SetError(NULL, MP_STANDARD_ERROR);

} else {

if (sem_post(self->handle) < 0)

return _PyMp_SetError(NULL, MP_STANDARD_ERROR);

Py_RETURN_FALSE;

}

#else

int sval;

if (SEM_GETVALUE(self->handle, &sval) < 0)

return _PyMp_SetError(NULL, MP_STANDARD_ERROR);

return PyBool_FromLong((long)sval == 0);

#endif

}

static PyObject *

semlock_afterfork(SemLockObject *self, PyObject *Py_UNUSED(ignored))

{

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 | METH_KEYWORDS,

"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,

""},

{"name", T_STRING, offsetof(SemLockObject, name), READONLY,

""},

{NULL}

};

* Semaphore type

PyTypeObject _PyMp_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_reserved */ 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,

};

* Function to unlink semaphore names

PyObject *

_PyMp_sem_unlink(PyObject *ignore, PyObject *args)

{

char *name;

if (!PyArg_ParseTuple(args, "s", &name))

return NULL;

if (SEM_UNLINK(name) < 0) {

_PyMp_SetError(NULL, MP_STANDARD_ERROR);

return NULL;

}

Py_RETURN_NONE;

}

cpython/Modules/_multiprocessing/semaphore.c at pythoncapi · pythoncapi/cpython · GitHub

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