Re-initialize the module threads lock upon fork.

python · ericsnowcurrently · May 15, 2023 · May 15, 2023 · May 15, 2023 · May 15, 2023
commit 82ff2ba965113b5417c8fcd3af1a07e0e6f4eae1
diff --git a/Lib/threading.py b/Lib/threading.py
@@ -49,6 +49,7 @@
 except AttributeError:
    _CRLock = None
 TIMEOUT_MAX = _thread.TIMEOUT_MAX
+_internal_after_fork = _thread._after_fork
 del _thread


@@ -1024,8 +1025,7 @@ def _set_tstate_lock(self):
        Set a lock object which will be released by the interpreter when
        the underlying thread state (see pystate.h) gets deleted.
        """
-        self._tstate_lock = _allocate_lock()
-        _set_sentinel(self._tstate_lock)
+        self._tstate_lock = _set_sentinel()
        self._tstate_lock.acquire()

        if not self.daemon:
@@ -1678,4 +1678,5 @@ def _after_fork():


 if hasattr(_os, "register_at_fork"):
+    _os.register_at_fork(after_in_child=_internal_after_fork)
    _os.register_at_fork(after_in_child=_after_fork)
diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
@@ -54,6 +54,16 @@ module_threads_init(struct module_threads *threads)
    return 0;
 }

+static int
+module_threads_reinit(struct module_threads *threads)
+{
+    if (_PyThread_at_fork_reinit(threads->mutex) < 0) {
+        PyErr_SetString(ThreadError, "failed to reinitialize lock at fork");
+        return -1;
+    }
+    return 0;
+}
+
 static void
 module_threads_fini(struct module_threads *threads)
 {
@@ -1477,11 +1487,12 @@ release_sentinel(void *wr_raw)
 }

 static PyObject *
-thread__set_sentinel(PyObject *module, PyObject *arg)
+thread__set_sentinel(PyObject *module, PyObject *Py_UNUSED(ignored))
 {
    PyObject *wr;
    PyThreadState *tstate = _PyThreadState_GET();
-    lockobject *lock = (lockobject *)arg;
+    thread_module_state *state = get_thread_state(module);
+    lockobject *lock;

    if (tstate->on_delete_data != NULL) {
        /* We must support the re-creation of the lock from a
@@ -1492,21 +1503,25 @@ thread__set_sentinel(PyObject *module, PyObject *arg)
        tstate->on_delete_data = NULL;
        Py_DECREF(wr);
    }
+    lock = newlockobject(state);
+    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;
-    Py_RETURN_NONE;
+    return (PyObject *) lock;
 }

 PyDoc_STRVAR(_set_sentinel_doc,
-"_set_sentinel(lock)\n\
+"_set_sentinel() -> lock\n\
 \n\
-Set the sentinel lock that will be released when the current thread\n\
+Set a sentinel lock that will be released when the current thread\n\
 state is finalized (after it is untied from the interpreter).\n\
 \n\
 This is a private API for the threading module.");
@@ -1707,6 +1722,16 @@ PyDoc_STRVAR(excepthook_doc,
 \n\
 Handle uncaught Thread.run() exception.");

+static PyObject *
+thread__after_fork(PyObject *module, PyObject *Py_UNUSED(ignored))
+{
+    thread_module_state *state = get_thread_state(module);
+    if (module_threads_reinit(&state->threads) < 0) {
+        return NULL;
+    }
+    Py_RETURN_NONE;
+}
+
 static PyMethodDef thread_methods[] = {
    {"start_new_thread",        (PyCFunction)thread_PyThread_start_new_thread,
     METH_VARARGS, start_new_doc},
@@ -1735,9 +1760,11 @@ static PyMethodDef thread_methods[] = {
    {"stack_size",              (PyCFunction)thread_stack_size,
     METH_VARARGS, stack_size_doc},
    {"_set_sentinel",           thread__set_sentinel,
-     METH_O, _set_sentinel_doc},
-    {"_excepthook",              thread_excepthook,
+     METH_NOARGS, _set_sentinel_doc},
+    {"_excepthook",             thread_excepthook,
     METH_O, excepthook_doc},
+    {"_after_fork",             thread__after_fork,
+     METH_NOARGS, NULL},
    {NULL,                      NULL}           /* sentinel */
 };