cpython/Modules/_weakref.c

#include "Python.h"


#define GET_WEAKREFS_LISTPTR(o) \
        ((PyWeakReference **) PyObject_GET_WEAKREFS_LISTPTR(o))


static int
is_dead_weakref(PyObject *value)
{
    if (!PyWeakref_Check(value)) {
        PyErr_SetString(PyExc_TypeError, "not a weakref");
        return -1;
    }
    return PyWeakref_GET_OBJECT(value) == Py_None;
}

PyDoc_STRVAR(remove_dead_weakref__doc__,
"_remove_dead_weakref(dict, key) -- atomically remove key from dict\n"
"if it points to a dead weakref.");

static PyObject *
remove_dead_weakref(PyObject *self, PyObject *args)
{
    PyObject *dct, *key;

    if (!PyArg_ParseTuple(args, "O!O:_remove_dead_weakref",
                          &PyDict_Type, &dct, &key)) {
        return NULL;
    }
    if (_PyDict_DelItemIf(dct, key, is_dead_weakref) < 0) {
        if (PyErr_ExceptionMatches(PyExc_KeyError))
            /* This function is meant to allow safe weak-value dicts
               with GC in another thread (see issue #28427), so it's
               ok if the key doesn't exist anymore.
               */
            PyErr_Clear();
        else
            return NULL;
    }
    Py_RETURN_NONE;
}


PyDoc_STRVAR(weakref_getweakrefcount__doc__,
"getweakrefcount(object) -- return the number of weak references\n"
"to 'object'.");

static PyObject *
weakref_getweakrefcount(PyObject *self, PyObject *object)
{
    PyObject *result = NULL;

    if (PyType_SUPPORTS_WEAKREFS(Py_TYPE(object))) {
        PyWeakReference **list = GET_WEAKREFS_LISTPTR(object);

        result = PyInt_FromSsize_t(_PyWeakref_GetWeakrefCount(*list));
    }
    else
        result = PyInt_FromLong(0);

    return result;
}


PyDoc_STRVAR(weakref_getweakrefs__doc__,
"getweakrefs(object) -- return a list of all weak reference objects\n"
"that point to 'object'.");

static PyObject *
weakref_getweakrefs(PyObject *self, PyObject *object)
{
    PyObject *result = NULL;

    if (PyType_SUPPORTS_WEAKREFS(Py_TYPE(object))) {
        PyWeakReference **list = GET_WEAKREFS_LISTPTR(object);
        Py_ssize_t count = _PyWeakref_GetWeakrefCount(*list);

        result = PyList_New(count);
        if (result != NULL) {
            PyWeakReference *current = *list;
            Py_ssize_t i;
            for (i = 0; i < count; ++i) {
                PyList_SET_ITEM(result, i, (PyObject *) current);
                Py_INCREF(current);
                current = current->wr_next;
            }
        }
    }
    else {
        result = PyList_New(0);
    }
    return result;
}


PyDoc_STRVAR(weakref_proxy__doc__,
"proxy(object[, callback]) -- create a proxy object that weakly\n"
"references 'object'.  'callback', if given, is called with a\n"
"reference to the proxy when 'object' is about to be finalized.");

static PyObject *
weakref_proxy(PyObject *self, PyObject *args)
{
    PyObject *object;
    PyObject *callback = NULL;
    PyObject *result = NULL;

    if (PyArg_UnpackTuple(args, "proxy", 1, 2, &object, &callback)) {
        result = PyWeakref_NewProxy(object, callback);
    }
    return result;
}


static PyMethodDef
weakref_functions[] =  {
    {"getweakrefcount", weakref_getweakrefcount,        METH_O,
     weakref_getweakrefcount__doc__},
    {"getweakrefs",     weakref_getweakrefs,            METH_O,
     weakref_getweakrefs__doc__},
    {"proxy",           weakref_proxy,                  METH_VARARGS,
     weakref_proxy__doc__},
    {"_remove_dead_weakref", remove_dead_weakref,       METH_VARARGS,
     remove_dead_weakref__doc__},
    {NULL, NULL, 0, NULL}
};


PyMODINIT_FUNC
init_weakref(void)
{
    PyObject *m;

    m = Py_InitModule3("_weakref", weakref_functions,
                       "Weak-reference support module.");
    if (m != NULL) {
        Py_INCREF(&_PyWeakref_RefType);
        PyModule_AddObject(m, "ref",
                           (PyObject *) &_PyWeakref_RefType);
        Py_INCREF(&_PyWeakref_RefType);
        PyModule_AddObject(m, "ReferenceType",
                           (PyObject *) &_PyWeakref_RefType);
        Py_INCREF(&_PyWeakref_ProxyType);
        PyModule_AddObject(m, "ProxyType",
                           (PyObject *) &_PyWeakref_ProxyType);
        Py_INCREF(&_PyWeakref_CallableProxyType);
        PyModule_AddObject(m, "CallableProxyType",
                           (PyObject *) &_PyWeakref_CallableProxyType);
    }
}