From 8b9091fba07b813b7486ef8fef279f2bf950570b Mon Sep 17 00:00:00 2001 From: Jeffrey Yasskin Date: Fri, 28 Mar 2008 04:11:18 +0000 Subject: Kill a race in test_threading in which the exception info in a thread finishing up after it was joined had a traceback pointing to that thread's (deleted) target attribute, while the test was trying to check that the target was destroyed. Big thanks to Antoine Pitrou for diagnosing the race and pointing out sys.exc_clear() to kill the exception early. This fixes issue 2496. --- Lib/test/test_threading.py | 8 ++++++-- Lib/threading.py | 9 +++++++++ 2 files changed, 15 insertions(+), 2 deletions(-) diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py index e309a54..195c4e8 100644 --- a/Lib/test/test_threading.py +++ b/Lib/test/test_threading.py @@ -276,13 +276,17 @@ class ThreadTests(unittest.TestCase): weak_cyclic_object = weakref.ref(cyclic_object) cyclic_object.thread.join() del cyclic_object - self.assertEquals(None, weak_cyclic_object()) + self.assertEquals(None, weak_cyclic_object(), + msg=('%d references still around' % + sys.getrefcount(weak_cyclic_object()))) raising_cyclic_object = RunSelfFunction(should_raise=True) weak_raising_cyclic_object = weakref.ref(raising_cyclic_object) raising_cyclic_object.thread.join() del raising_cyclic_object - self.assertEquals(None, weak_raising_cyclic_object()) + self.assertEquals(None, weak_raising_cyclic_object(), + msg=('%d references still around' % + sys.getrefcount(weak_raising_cyclic_object()))) class ThreadingExceptionTests(unittest.TestCase): diff --git a/Lib/threading.py b/Lib/threading.py index 86153b0..eebe10a 100644 --- a/Lib/threading.py +++ b/Lib/threading.py @@ -392,6 +392,9 @@ class Thread(_Verbose): # shutdown and thus raises an exception about trying to perform some # operation on/with a NoneType __exc_info = _sys.exc_info + # Keep sys.exc_clear too to clear the exception just before + # allowing .join() to return. + __exc_clear = _sys.exc_clear def __init__(self, group=None, target=None, name=None, args=(), kwargs=None, verbose=None): @@ -527,6 +530,12 @@ class Thread(_Verbose): else: if __debug__: self._note("%s.__bootstrap(): normal return", self) + finally: + # Prevent a race in + # test_threading.test_no_refcycle_through_target when + # the exception keeps the target alive past when we + # assert that it's dead. + self.__exc_clear() finally: with _active_limbo_lock: self.__stop() -- cgit v0.12