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Make ffi_init_once thread-safe in free threaded build #143

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Make ffi_init_once thread-safe in free threaded build #143

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21 changes: 21 additions & 0 deletions src/c/_cffi_backend.c
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Original file line number Diff line number Diff line change
Expand Up @@ -204,6 +204,27 @@
# define USE_WRITEUNRAISABLEMSG
#endif

#if PY_VERSION_HEX <= 0x030d00a1
static int PyDict_GetItemRef(PyObject *mp, PyObject *key, PyObject **result)
{
PyObject *obj = PyDict_GetItemWithError(mp, key);
Py_XINCREF(obj);
*result = obj;
if (obj == NULL) {
if (PyErr_Occurred()) {
return -1;
}
return 0;
}
return 1;
}
#endif

#if PY_VERSION_HEX <= 0x030d00b3
# define Py_BEGIN_CRITICAL_SECTION(op) {
# define Py_END_CRITICAL_SECTION() }
#endif

/************************************************************/

/* base type flag: exactly one of the following: */
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21 changes: 13 additions & 8 deletions src/c/ffi_obj.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1001,16 +1001,21 @@ static PyObject *ffi_init_once(FFIObject *self, PyObject *args, PyObject *kwds)
in this function */

/* atomically get or create a new dict (no GIL release) */
Py_BEGIN_CRITICAL_SECTION(self);
cache = self->init_once_cache;
if (cache == NULL) {
cache = PyDict_New();
if (cache == NULL)
return NULL;
self->init_once_cache = cache;
self->init_once_cache = cache = PyDict_New();
}
Py_END_CRITICAL_SECTION();

if (cache == NULL) {
return NULL;
}

/* get the tuple from cache[tag], or make a new one: (False, lock) */
tup = PyDict_GetItem(cache, tag);
if (PyDict_GetItemRef(cache, tag, &tup) < 0) {
return NULL;
}
if (tup == NULL) {
lock = PyThread_allocate_lock();
if (lock == NULL)
Expand All @@ -1033,17 +1038,17 @@ static PyObject *ffi_init_once(FFIObject *self, PyObject *args, PyObject *kwds)
Py_DECREF(x);
if (tup == NULL)
return NULL;

Py_DECREF(tup); /* there is still a ref inside the dict */
}

res = PyTuple_GET_ITEM(tup, 1);
Py_INCREF(res);

if (PyTuple_GET_ITEM(tup, 0) == Py_True) {
/* tup == (True, result): return the result. */
Py_DECREF(tup);
return res;
}
Py_DECREF(tup);

/* tup == (False, lock) */
lockobj = res;
Expand All @@ -1058,7 +1063,7 @@ static PyObject *ffi_init_once(FFIObject *self, PyObject *args, PyObject *kwds)
PyThread_acquire_lock(lock, WAIT_LOCK);
Py_END_ALLOW_THREADS

x = PyDict_GetItem(cache, tag);
x = PyDict_GetItem(cache, tag); /* protected by lock */
if (x != NULL && PyTuple_GET_ITEM(x, 0) == Py_True) {
/* the real result was put in the dict while we were waiting
for PyThread_acquire_lock() above */
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