python3 multiprocessing Semaphore

http://mirror.hust.edu.cn/gnu/glibc/
glibc-2.29.tar.gz

glibc:  bits/semaphore.h

#if __WORDSIZE == 64
# define __SIZEOF_SEM_T    32
#else
# define __SIZEOF_SEM_T    16
#endif


/* Value returned if `sem_open' failed.  */
#define SEM_FAILED      ((sem_t *) 0)


typedef union
{
  char __size[__SIZEOF_SEM_T];
  long int __align;
} sem_t;



    PyModule_AddObject(module, "SemLock", (PyObject*)&_PyMp_SemLockType);



Python-3.6.8/Modules/_multiprocessing/multiprocessing.h

     typedef sem_t *SEM_HANDLE;

Python-3.6.8/Modules/_multiprocessing/semaphore.c

enum { RECURSIVE_MUTEX, SEMAPHORE };

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


/*
 * 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,
};


static PyObject *
semlock_acquire(SemLockObject *self, PyObject *args, PyObject *kwds)
{

等等的实现



multiprocessing/synchronize.py

class SemLock(object):
    def __init__(self, kind, value, maxvalue, *, ctx):
        if ctx is None:
            ctx = context._default_context.get_context()
        name = ctx.get_start_method()
        unlink_now = sys.platform == 'win32' or name == 'fork'
        for i in range(100):
            try:
                sl = self._semlock = _multiprocessing.SemLock(
                    kind, value, maxvalue, self._make_name(),
                    unlink_now)


class Semaphore(SemLock):

    def __init__(self, value=1, *, ctx):
        SemLock.__init__(self, SEMAPHORE, value, SEM_VALUE_MAX, ctx=ctx)