gh-119585: Fix crash involving `PyGILState_Release()` and `PyThreadState_Clear()` (#119753)

Make sure that `gilstate_counter` is not zero in when calling
`PyThreadState_Clear()`. A destructor called from `PyThreadState_Clear()` may
call back into `PyGILState_Ensure()` and `PyGILState_Release()`. If
`gilstate_counter` is zero, it will try to create a new thread state before
the current active thread state is destroyed, leading to an assertion failure
or crash.

1 files changed, 9 insertions, 0 deletions

diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index f99ebf0..b58c172 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -764,6 +764,14 @@ test_thread_state(PyObject *self, PyObject *args)
     Py_RETURN_NONE;
 }
 
+static PyObject *
+gilstate_ensure_release(PyObject *module, PyObject *Py_UNUSED(ignored))
+{
+    PyGILState_STATE state = PyGILState_Ensure();
+    PyGILState_Release(state);
+    Py_RETURN_NONE;
+}
+
 #ifndef MS_WINDOWS
 static PyThread_type_lock wait_done = NULL;
 
@@ -3351,6 +3359,7 @@ static PyMethodDef TestMethods[] = {
     {"test_get_type_dict",        test_get_type_dict,            METH_NOARGS},
     {"test_reftracer",          test_reftracer,                  METH_NOARGS},
     {"_test_thread_state",      test_thread_state,               METH_VARARGS},
+    {"gilstate_ensure_release", gilstate_ensure_release,         METH_NOARGS},
 #ifndef MS_WINDOWS
     {"_spawn_pthread_waiter",   spawn_pthread_waiter,            METH_NOARGS},
     {"_end_spawned_pthread",    end_spawned_pthread,             METH_NOARGS},