gh-153020: Fix race condition on event_tstate in _tkinter

Author: tangyuan0821

Modules/_tkinter.c

@@ -3655,7 +3655,7 @@ EventHook(void)
     int tfile;
     stdin_ready = 0;
 #endif
-    PyEval_RestoreThread(event_tstate);
+    PyEval_RestoreThread(_Py_atomic_load_ptr(&event_tstate));
     errorInCmd = 0;
 #ifdef MS_WINDOWS
     hStdin = GetStdHandle(STD_INPUT_HANDLE);
@@ -3687,7 +3687,7 @@ EventHook(void)
 #endif
         Py_BEGIN_ALLOW_THREADS
         if(tcl_lock)PyThread_acquire_lock(tcl_lock, 1);
-        tcl_tstate = event_tstate;
+        tcl_tstate = _Py_atomic_load_ptr(&event_tstate);
 
         result = Tcl_DoOneEvent(TCL_DONT_WAIT);
 
@@ -3725,7 +3725,7 @@ EnableEventHook(void)
 {
 #ifdef WAIT_FOR_STDIN
     if (PyOS_InputHook == NULL) {
-        event_tstate = PyThreadState_Get();
+        _Py_atomic_store_ptr(&event_tstate, PyThreadState_Get());
         PyOS_InputHook = EventHook;
     }
 #endif
@@ -3737,6 +3737,7 @@ DisableEventHook(void)
 #ifdef WAIT_FOR_STDIN
     if (Tk_GetNumMainWindows() == 0 && PyOS_InputHook == EventHook) {
         PyOS_InputHook = NULL;
+        _Py_atomic_store_ptr(&event_tstate, NULL);
     }
 #endif
 }