bpo-44032: Defer clearing last thread state until last GC has been run. by markshannon · Pull Request #26285 · python/cpython

markshannon

	release_sentinel(void *wr_raw)
	{
	PyObject *wr = _PyObject_CAST(wr_raw);
	/* Tricky: this function is called when the current thread state
	is being deleted. Therefore, only simple C code can safely
	execute here. */
	PyObject *obj = PyWeakref_GET_OBJECT(wr);
	lockobject *lock;
	if (obj != Py_None) {
	lock = (lockobject *) obj;
	if (lock->locked) {
	PyThread_release_lock(lock->lock_lock);
	lock->locked = 0;
	}
	}
	/* Deallocating a weakref with a NULL callback only calls
	PyObject_GC_Del(), which can't call any Python code. */
	Py_DECREF(wr);
	}

	static PyObject *
	thread__set_sentinel(PyObject module, PyObject Py_UNUSED(ignored))
	{
	PyObject *wr;
	PyThreadState *tstate = PyThreadState_Get();
	lockobject *lock;

	if (tstate->on_delete_data != NULL) {
	/* We must support the re-creation of the lock from a
	fork()ed child. */
	assert(tstate->on_delete == &release_sentinel);
	wr = (PyObject *) tstate->on_delete_data;
	tstate->on_delete = NULL;
	tstate->on_delete_data = NULL;
	Py_DECREF(wr);
	}
	lock = newlockobject(module);
	if (lock == NULL)
	return NULL;
	/* The lock is owned by whoever called _set_sentinel(), but the weakref
	hangs to the thread state. */
	wr = PyWeakref_NewRef((PyObject *) lock, NULL);
	if (wr == NULL) {
	Py_DECREF(lock);
	return NULL;
	}
	tstate->on_delete_data = (void *) wr;
	tstate->on_delete = &release_sentinel;
	return (PyObject *) lock;
	}