From 66e2fb68aca2a2678a327b200e657b761f358bc1 Mon Sep 17 00:00:00 2001
From: Ross Lagerwall <rosslagerwall@gmail.com>
Date: Sun, 8 Jan 2012 08:29:40 +0200
Subject: [PATCH] Issue #12364: Fix a hang in
 concurrent.futures.ProcessPoolExecutor.

---
 Lib/concurrent/futures/process.py   | 7 +------
 Lib/test/test_concurrent_futures.py | 6 ++++++
 Misc/NEWS                           | 4 ++++
 3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/Lib/concurrent/futures/process.py b/Lib/concurrent/futures/process.py
index 80829406774..d3bbe2c5e68 100644
--- a/Lib/concurrent/futures/process.py
+++ b/Lib/concurrent/futures/process.py
@@ -213,9 +213,7 @@ def shutdown_one_process():
                 work_item.future.set_exception(result_item.exception)
             else:
                 work_item.future.set_result(result_item.result)
-            continue
-        # If we come here, we either got a timeout or were explicitly woken up.
-        # In either case, check whether we should start shutting down.
+        # Check whether we should start shutting down.
         executor = executor_reference()
         # No more work items can be added if:
         #   - The interpreter is shutting down OR
@@ -234,9 +232,6 @@ def shutdown_one_process():
                     p.join()
                 call_queue.close()
                 return
-            else:
-                # Start shutting down by telling a process it can exit.
-                shutdown_one_process()
         del executor
 
 _system_limits_checked = False
diff --git a/Lib/test/test_concurrent_futures.py b/Lib/test/test_concurrent_futures.py
index 6cc57f85d0b..372da27dca3 100644
--- a/Lib/test/test_concurrent_futures.py
+++ b/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):
diff --git a/Misc/NEWS b/Misc/NEWS
index 9212f9e6229..8e95abb6183 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -97,6 +97,10 @@ 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.