Patch up race condition exposed in #478

DMOJ · Sep 29, 2019 · 59d7b83 · 59d7b83
1 parent a6a1a74
commit 59d7b83
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/dmoj/judge.py b/dmoj/judge.py
@@ -173,7 +173,8 @@ def grading_cleanup_wrapper():
         self.current_submission_thread.daemon = True
         self.current_submission_thread.start()
 
-        if blocking:
+        # Submission may have been killed already, but block if it hasn't been.
+        if blocking and self.current_submission_thread is not None:
             self.current_submission_thread.join()
 
     def grade_cases(self, grader, cases, short_circuit=False, is_short_circuiting=False):