avoid a deadlock with the interpreter head lock and the GIL during finalization

Python/pystate.c

@@ -315,7 +315,14 @@ PyThreadState_DeleteCurrent()
         Py_FatalError(
             "PyThreadState_DeleteCurrent: no current tstate");
     _PyThreadState_Current = NULL;
-    tstate_delete_common(tstate);
+    /*
+      Only call tstate_delete_common to have the tstate if we're not finalizing
+      or we're the main thread. The main thread will do this for us. Not calling
+      tstate_delete_common means we won't lock the interpreter head lock,
+      avoiding a possible deadlock with the GIL.
+    */
+    if (!_Py_Finalizing || _Py_Finalizing == tstate)
+        tstate_delete_common(tstate);
     if (autoInterpreterState && PyThread_get_key_value(autoTLSkey) == tstate)
         PyThread_delete_key_value(autoTLSkey);
     PyEval_ReleaseLock();