_threadmodule: make _thread.lock thread-safe

Previously, _thread.lock would modify a shared boolean "locked" after
the underlying lock was released. This swaps the order of those
statements.

Author: colesbury

Modules/_threadmodule.c

@@ -206,8 +206,8 @@ lock_PyThread_release_lock(lockobject *self, PyObject *Py_UNUSED(ignored))
         return NULL;
     }
 
-    PyThread_release_lock(self->lock_lock);
     self->locked = 0;
+    PyThread_release_lock(self->lock_lock);
     Py_RETURN_NONE;
 }
 
@@ -1393,8 +1393,8 @@ release_sentinel(void *wr_raw)
     if (obj != Py_None) {
         lock = (lockobject *) obj;
         if (lock->locked) {
-            PyThread_release_lock(lock->lock_lock);
             lock->locked = 0;
+            PyThread_release_lock(lock->lock_lock);
         }
         Py_DECREF(obj);
     }