[Python-checkins] cpython: Issue #16284: Prevent keeping unnecessary references to worker functions in

Sat Nov 3 14:36:12 CET 2012

http://hg.python.org/cpython/rev/70cef0a160cf
changeset: 80188:70cef0a160cf
user: Andrew Svetlov <andrew.svetlov at gmail.com>
date: Sat Nov 03 15:36:01 2012 +0200
summary:
 Issue #16284: Prevent keeping unnecessary references to worker functions in concurrent.futures ThreadPoolExecutor.
files:
 Lib/concurrent/futures/process.py | 4 +++
 Lib/concurrent/futures/thread.py | 2 +
 Lib/multiprocessing/queues.py | 4 +++
 Lib/test/test_concurrent_futures.py | 22 +++++++++++++++++
 Misc/ACKS | 1 +
 Misc/NEWS | 3 ++
 6 files changed, 36 insertions(+), 0 deletions(-)

diff --git a/Lib/concurrent/futures/process.py b/Lib/concurrent/futures/process.py
--- a/Lib/concurrent/futures/process.py
+++ b/Lib/concurrent/futures/process.py
@@ -240,6 +240,8 @@
 "terminated abruptly while the future was "
 "running or pending."
 ))
+ # Delete references to object. See issue16284
+ del work_item
 pending_work_items.clear()
 # Terminate remaining workers forcibly: the queues or their
 # locks may be in a dirty state and block forever.
@@ -264,6 +266,8 @@
 work_item.future.set_exception(result_item.exception)
 else:
 work_item.future.set_result(result_item.result)
+ # Delete references to object. See issue16284
+ del work_item
 # Check whether we should start shutting down.
 executor = executor_reference()
 # No more work items can be added if:
diff --git a/Lib/concurrent/futures/thread.py b/Lib/concurrent/futures/thread.py
--- a/Lib/concurrent/futures/thread.py
+++ b/Lib/concurrent/futures/thread.py
@@ -63,6 +63,8 @@
 work_item = work_queue.get(block=True)
 if work_item is not None:
 work_item.run()
+ # Delete references to object. See issue16284
+ del work_item
 continue
 executor = executor_reference()
 # Exit if:
diff --git a/Lib/multiprocessing/queues.py b/Lib/multiprocessing/queues.py
--- a/Lib/multiprocessing/queues.py
+++ b/Lib/multiprocessing/queues.py
@@ -243,10 +243,14 @@
 
 if wacquire is None:
 send(obj)
+ # Delete references to object. See issue16284
+ del obj
 else:
 wacquire()
 try:
 send(obj)
+ # Delete references to object. See issue16284
+ del obj
 finally:
 wrelease()
 except IndexError:
diff --git a/Lib/test/test_concurrent_futures.py b/Lib/test/test_concurrent_futures.py
--- a/Lib/test/test_concurrent_futures.py
+++ b/Lib/test/test_concurrent_futures.py
@@ -15,6 +15,7 @@
 import threading
 import time
 import unittest
+import weakref
 
 from concurrent import futures
 from concurrent.futures._base import (
@@ -52,6 +53,11 @@
 sys.stdout.flush()
 
 
+class MyObject(object):
+ def my_method(self):
+ pass
+
+
 class ExecutorMixin:
 worker_count = 5
 
@@ -396,6 +402,22 @@
 self.executor.map(str, [2] * (self.worker_count + 1))
 self.executor.shutdown()
 
+ @test.support.cpython_only
+ def test_no_stale_references(self):
+ # Issue #16284: check that the executors don't unnecessarily hang onto
+ # references.
+ my_object = MyObject()
+ my_object_collected = threading.Event()
+ my_object_callback = weakref.ref(
+ my_object, lambda obj: my_object_collected.set())
+ # Deliberately discarding the future.
+ self.executor.submit(my_object.my_method)
+ del my_object
+
+ collected = my_object_collected.wait(timeout=5.0)
+ self.assertTrue(collected,
+ "Stale reference not collected within timeout.")
+
 
 class ThreadPoolExecutorTest(ThreadPoolMixin, ExecutorTest):
 def test_map_submits_without_iteration(self):
diff --git a/Misc/ACKS b/Misc/ACKS
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -726,6 +726,7 @@
 Loren Luke
 Fredrik Lundh
 Mark Lutz
+Taras Lyapun
 Jim Lynch
 Mikael Lyngvig
 Martin von Löwis
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -88,6 +88,9 @@
 Library
 -------
 
+- Issue #16284: Prevent keeping unnecessary references to worker functions
+ in concurrent.futures ThreadPoolExecutor.
+
 - Issue #1207589: Add Cut/Copy/Paste items to IDLE right click Context Menu
 Patch by Todd Rovito.
 
-- 
Repository URL: http://hg.python.org/cpython
