Close the call queue in concurrent.futures.ProcessPoolExecutor when

shutdown() is called, without waiting for the garbage collector to kick in.

Lib/concurrent/futures/process.py

@@ -232,6 +232,7 @@ def _queue_management_worker(executor_reference,
                 # X.
                 for p in processes:
                     p.join()
+                call_queue.close()
                 return
             else:
                 # Start shutting down by telling a process it can exit.

Misc/NEWS

@@ -30,6 +30,9 @@ Core and Builtins
 Library
 -------
 
+- Close the call queue in concurrent.futures.ProcessPoolExecutor when
+  shutdown() is called, without waiting for the garbage collector to kick in.
+
 - Issue #11603: Fix a crash when __str__ is rebound as __repr__.  Patch by
   Andreas Stührk.