I didn't understand the purpose of the issue #19334: it doesn't mention the OS nor the test. I prefer to create a more specific issue, so here you have one specific hang.

http://buildbot.python.org/all/builders/AMD64%20Snow%20Leop%203.x/builds/517/steps/test/logs/stdio

[385/385] test_asyncio
Timeout (1:00:00)!
Thread 0x00007fff71296cc0 (most recent call first):
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/selectors.py", line 291 in select
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/asyncio/base_events.py", line 614 in _run_once
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/asyncio/base_events.py", line 153 in run_forever
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/asyncio/base_events.py", line 172 in run_until_complete
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/test_asyncio/test_events.py", line 1155 in test_subprocess_send_signal
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/case.py", line 571 in run
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/case.py", line 610 in __call__
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 117 in run
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 79 in __call__
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 117 in run
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 79 in __call__
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 117 in run
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/suite.py", line 79 in __call__
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/unittest/runner.py", line 168 in run
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/support/__init__.py", line 1685 in _run_suite
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/support/__init__.py", line 1719 in run_unittest
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/test_asyncio/__init__.py", line 31 in test_main
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/regrtest.py", line 1276 in runtest_inner
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/regrtest.py", line 965 in runtest
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/regrtest.py", line 532 in main
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/regrtest.py", line 1560 in main_in_temp_cwd
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/regrtest.py", line 1585 in <module>
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/runpy.py", line 73 in _run_code
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/runpy.py", line 160 in _run_module_as_main
Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/runpy.py", line 160, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/runpy.py", line 73, in _run_code
    exec(code, run_globals)
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/__main__.py", line 3, in <module>
    regrtest.main_in_temp_cwd()
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/regrtest.py", line 1560, in main_in_temp_cwd
    main()
  File "/Users/buildbot/buildarea/3.x.murray-snowleopard/build/Lib/test/regrtest.py", line 736, in main
    raise Exception("Child error on {}: {}".format(test, result[1]))
Exception: Child error on test_asyncio: Exit code 1
make: *** [buildbottest] Error 1