Prevent adding pending calls if finalizing.

Author: ericsnowcurrently

Include/internal/pycore_pystate.h

@@ -32,6 +32,8 @@ struct _is {
     int64_t id_refcount;
     PyThread_type_lock id_mutex;
 
+    int finalizing;
+
     PyObject *modules;
     PyObject *modules_by_index;
     PyObject *sysdict;

Python/ceval.c

@@ -386,10 +386,21 @@ _Py_AddPendingCall(PyInterpreterState *interp, int (*func)(void *), void *arg)
             return -1;
     }
 
-    int result = _add_pending_call(interp, func, arg);
+    int result = -1;
+    if (interp->finalizing) {
+        PyObject *exc, *val, *tb;
+        PyErr_Fetch(&exc, &val, &tb);
+        PyErr_SetString(PyExc_SystemError, "Py_AddPendingCall: cannot add pending calls (interpreter shutting down)");
+        PyErr_Print();
+        PyErr_Restore(exc, val, tb);
+        goto done;
+    }
+
+    result = _add_pending_call(interp, func, arg);
     /* signal main loop */
     SIGNAL_PENDING_CALLS(interp);
 
+done:
     if (lock != NULL)
         PyThread_release_lock(lock);
     return result;

Python/pylifecycle.c

@@ -1459,8 +1459,19 @@ Py_EndInterpreter(PyThreadState *tstate)
     if (tstate->frame != NULL)
         Py_FatalError("Py_EndInterpreter: thread still has a frame");
 
+    // Mark as finalizing.
+    if (interp->ceval.pending.lock != NULL) {
+        PyThread_acquire_lock(interp->ceval.pending.lock, 1);
+    }
+    interp->finalizing = 1;
+    if (interp->ceval.pending.lock != NULL) {
+        PyThread_release_lock(interp->ceval.pending.lock);
+    }
+
+    // Wrap up existing threads.
     wait_for_thread_shutdown();
 
+    // Make any pending calls.
     if (_Py_atomic_load_relaxed(
                 &(interp->ceval.pending.calls_to_do)))
     {