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.

1 files changed, 6 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):