http://buildbot.python.org/all/builders/AMD64%20Debian%20root%202.7/builds/154/steps/test/logs/stdio0:04:59 [312/402/1] test_thread failedTraceback (most recent call last):  File "/root/buildarea/2.7.angelico-debian-amd64/build/Lib/test/test_thread.py", line 133, in task    raise SyntaxErrorSyntaxError: Nonetest test_thread failed -- Traceback (most recent call last):  File "/root/buildarea/2.7.angelico-debian-amd64/build/Lib/test/test_thread.py", line 150, in test_save_exception_state_on_error    self.assertIn("Traceback", stderr.getvalue())AssertionError: 'Traceback' not found in 'Unhandled exception in thread started by <function task at 0x7f06c77ab1b0>\n'

I just encountered with this failure. It is random, I can reproduce it only when run test_thread repeatedly in parallel with running other tests (maybe needed high load factor).$ ./python -m test -uall -F test_thread test_thread test_thread test_thread Run tests sequentially0:00:00 [  1] test_thread0:00:00 [  2] test_threadTraceback (most recent call last):  File "/home/serhiy/py/cpython2.7/Lib/test/test_thread.py", line 133, in task    raise SyntaxErrorSyntaxError: Nonetest test_thread failed -- Traceback (most recent call last):  File "/home/serhiy/py/cpython2.7/Lib/test/test_thread.py", line 150, in test_save_exception_state_on_error    self.assertIn("Traceback", stderr.getvalue())AssertionError: 'Traceback' not found in 'Unhandled exception in thread started by <function task at 0xb6a89ee4>\n'1 test OK.1 test failed:    test_threadTotal duration: 432 msTests result: FAILURE[50664 refs]

Problem is with test test_thread.ThreadRunningTests.test_save_exception_state_on_error when other tests leave threads runnig. test_save_exception_state_on_error relay on thread._get_count(), if this value decrease test assume thread is finished with is not always correct (other threads finish - started by different test).Fix is to make sure each test wait for all threads to finsh.

The solution inPR 1583 looks unsafe to me. If some threads hang the loop `while self.thread_count != thread._count()` will never finished. If some dangling threads created in other tests or by regrtest itself are finished during running the test_thread test, that loop will never finished too.

Using 5 terminals to run 5 tests in parallel.I'm unable to reproduce the bug if I only run the test alone:   ./python -m test -uall -F -m test_save_exception_state_on_error test_threadBut I'm able to reproduce the bug if I run the full test_thread.py:   ./python -m test -uall -F test_threadSo I'm now more confident that grzgrzgrz3's patch can fix the issue. test_thread uses the low-level thread.start_new_thread() function to spawn threads, but pthread_join() is not used to wait for the thread exit. So multiple test_thread tests can "leak" threads which can have random effect on following tests.

New changeset79ef7f8e88a4972c4aecf95cfc5cd934f1861e08 by Victor Stinner in branch 'master':bpo-30357: test_thread now uses threading_cleanup() (#1592)https://github.com/python/cpython/commit/79ef7f8e88a4972c4aecf95cfc5cd934f1861e08

I think this do not solve this issue yet. There is still posibillity that different tests/testrunners spawn threads and 'fool' testcase. I think we should not relay on `thread._count` value where it's possible. For master branch `thread._set_sentinel()` can be used. For 2.7 i don't know simple solution.I would like to know your opinion it is worth changing?

There is still posibillity that different tests/testrunners spawn threadsand 'fool' testcase.If you run multiple test files in parallel, each test runner process runs asingle test at the same time: test methods are run sequentially to preventside effects.

New changeset6924ed55c9807d69757e03bbe1caeec1104efacb by Victor Stinner (grzgrzgrz3) in branch '2.7':bpo-30357 each test in test_thread waits until all spawned threads finish (#1583)https://github.com/python/cpython/commit/6924ed55c9807d69757e03bbe1caeec1104efacb

Backported to 3.5 (aeb644714d37fb974e3acdf7daef031461e1283f) and 3.6 (6b5b85aecf4db796a05582202a6c875b36eae516).I now close the issue, I consider that the change should fix the randomly failing test. If the failure comes back, I will reopen the issue.Thank you very much Grzegorz Grzywacz for your first contribution!

New changesetf8d05b3a24e745ab4a974b891ac1389e2f11ce4d by Victor Stinner in branch 'master':bpo-30387: Fix warning in test_threading (#1634)https://github.com/python/cpython/commit/f8d05b3a24e745ab4a974b891ac1389e2f11ce4d

New changeset44944b602af23712d7119801183cdc6e202e4f76 by Victor Stinner in branch '3.6':bpo-30387: Fix warning in test_threading (#1634) (#1636)https://github.com/python/cpython/commit/44944b602af23712d7119801183cdc6e202e4f76

New changesetf5633e02433a81a6d0f14fc1c3294e752f4ac1a3 by Victor Stinner in branch '3.5':bpo-30387: Fix warning in test_threading (#1634) (#1637)https://github.com/python/cpython/commit/f5633e02433a81a6d0f14fc1c3294e752f4ac1a3