Mark ProcessPoolExecutor shutdown from queue management thread if shutting down

Author: mrknmc

Lib/concurrent/futures/process.py

@@ -421,6 +421,10 @@ def shutdown_worker():
         #   - The executor that owns this worker has been shutdown.
         if shutting_down():
             try:
+                # Flag the executor as shutting down as early as possible if it
+                # is not gc-ed yet.
+                if executor is not None:
+                    executor._shutdown_thread = True
                 # Since no new work items can be added, it is safe to shutdown
                 # this thread if there are no pending work items.
                 if not pending_work_items: