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Minor cleanup of the new scheme for detecting thread termination. 

Documented some obscurities, and assert'ed ._stop()'s crucial precondition.
This commit is contained in:
Tim Peters 2013-09-09 12:57:10 -05:00
parent 8568f66daf
commit 7a6054b19d
1 changed files with 26 additions and 5 deletions
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31
Lib/threading.py
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@ -703,8 +703,28 @@ class Thread:
pass
def _stop(self):
self._is_stopped = True
self._tstate_lock = None
# After calling .stop(), .is_alive() returns False and .join() returns
# immediately. ._tstate_lock must be released before calling ._stop().
#
# Normal case: C code at the end of the thread's life
# (release_sentinel in _threadmodule.c) releases ._tstate_lock, and
# that's detected by our ._wait_for_tstate_lock(), called by .join()
# and .is_alive(). Any number of threads _may_ call ._stop()
# simultaneously (for example, if multiple threads are blocked in
# .join() calls), and they're not serialized. That's harmless -
# they'll just make redundant rebindings of ._is_stopped and
# ._tstate_lock. Obscure: we rebind ._tstate_lock last so that the
# "assert self._is_stopped" in ._wait_for_tstate_lock() always works
# (the assert is executed only if ._tstate_lock is None).
#
# Special case: _main_thread releases ._tstate_lock via this module's
# _shutdown() function.
tlock = self._tstate_lock
if tlock is not None:
# It's OK if multiple threads get in here (see above).
assert not tlock.locked()
self._is_stopped = True
self._tstate_lock = None
def _delete(self):
"Remove current thread from the dict of currently running threads."
@ -921,9 +941,10 @@ def _shutdown():
# the main thread's tstate_lock - that won't happen until the interpreter
# is nearly dead. So we release it here. Note that just calling _stop()
# isn't enough: other threads may already be waiting on _tstate_lock.
assert _main_thread._tstate_lock is not None
assert _main_thread._tstate_lock.locked()
_main_thread._tstate_lock.release()
tlock = _main_thread._tstate_lock
assert tlock is not None
assert tlock.locked()
tlock.release()
_main_thread._stop()
t = _pickSomeNonDaemonThread()
while t: