test_multiprocessing segfaults in a loop. The crash occurs in _Condition.release() on waiter.release(), called from Queue._finalize_close(). Possible related changes:

 - a5c8b6ebe895: new sigwait() test using thread (issue #8407)
 - 6d6099f7fe89: add sentinels to multiprocessing (issue #9205)

Example of a crash:

[333/356/1] test_multiprocessing
Fatal Python error: Segmentation fault

Thread 0x01cde800:
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/threading.py", line 237 in wait
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/multiprocessing/queues.py", line 252 in _feed
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/threading.py", line 690 in run
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/threading.py", line 737 in _bootstrap_inner
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/threading.py", line 710 in _bootstrap

Current thread 0xa000d000:
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/threading.py", line 298 in notify
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/multiprocessing/queues.py", line 227 in _finalize_close
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/multiprocessing/util.py", line 202 in __call__
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/multiprocessing/process.py", line 270 in _bootstrap
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/multiprocessing/forking.py", line 133 in __init__
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/multiprocessing/process.py", line 134 in start
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/multiprocessing/pool.py", line 220 in _repopulate_pool
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/multiprocessing/pool.py", line 157 in __init__
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/multiprocessing/__init__.py", line 231 in Pool
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/test/test_multiprocessing.py", line 2186 in test_main
  File "./Lib/test/regrtest.py", line 1043 in runtest_inner
  File "./Lib/test/regrtest.py", line 841 in runtest
  File "./Lib/test/regrtest.py", line 668 in main
  File "./Lib/test/regrtest.py", line 1618 in <module>

There are approximatively 698 crashes in last tests on "x86 Tiger 3.x"!
http://www.python.org/dev/buildbot/all/builders/x86%20Tiger%203.x/builds/2722/steps/test/logs/stdio

Most occured on Queue._finalize_close() -> _Condition.release() -> waiter.release().