Merge with 3.2 for #12364.

Lib/concurrent/futures/process.py

@@ -273,9 +273,6 @@ def shutdown_worker():
                 if not pending_work_items:
                     shutdown_worker()
                     return
-                else:
-                    # Start shutting down by telling a process it can exit.
-                    call_queue.put_nowait(None)
             except Full:
                 # This is not a problem: we will eventually be woken up (in
                 # result_queue.get()) and be able to send a sentinel again.

Lib/test/test_concurrent_futures.py

@@ -109,6 +109,12 @@ def test_interpreter_shutdown(self):
         self.assertFalse(err)
         self.assertEqual(out.strip(), b"apple")
 
+    def test_hang_issue12364(self):
+        fs = [self.executor.submit(time.sleep, 0.1) for _ in range(50)]
+        self.executor.shutdown()
+        for f in fs:
+            f.result()
+
 
 class ThreadPoolShutdownTest(ThreadPoolMixin, ExecutorShutdownTest):
     def _prime_executor(self):

Misc/NEWS

@@ -422,6 +422,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #12364: Fix a hang in concurrent.futures.ProcessPoolExecutor.
+  The hang would occur when retrieving the result of a scheduled future after
+  the executor had been shut down.
+
 - Issue #13502: threading: Fix a race condition in Event.wait() that made it
   return False when the event was set and cleared right after.