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[2.7] bpo-8799: Reduce timing sensitivity of condition test by explicitly #2320

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Merged
vstinner merged 1 commit into from
Jun 22, 2017
Merged

[2.7] bpo-8799: Reduce timing sensitivity of condition test by explicitly #2320

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15 changes: 15 additions & 0 deletions Lib/test/lock_tests.py
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Original file line number Diff line number Diff line change
Expand Up @@ -347,6 +347,17 @@ def test_unacquired_notify(self):
self.assertRaises(RuntimeError, cond.notify)

def _check_notify(self, cond):
# Note that this test is sensitive to timing. If the worker threads
# don't execute in a timely fashion, the main thread may think they
# are further along then they are. The main thread therefore issues
# _wait() statements to try to make sure that it doesn't race ahead
# of the workers.
# Secondly, this test assumes that condition variables are not subject
# to spurious wakeups. The absence of spurious wakeups is an implementation
# detail of Condition Cariables in current CPython, but in general, not
# a guaranteed property of condition variables as a programming
# construct. In particular, it is possible that this can no longer
# be conveniently guaranteed should their implementation ever change.
N = 5
results1 = []
results2 = []
Expand Down Expand Up @@ -374,6 +385,9 @@ def f():
_wait()
self.assertEqual(results1, [1] * 3)
self.assertEqual(results2, [])
# first wait, to ensure all workers settle into cond.wait() before
# we continue. See issue #8799
_wait()
# Notify 5 threads: they might be in their first or second wait
cond.acquire()
cond.notify(5)
Expand All @@ -384,6 +398,7 @@ def f():
_wait()
self.assertEqual(results1, [1] * 3 + [2] * 2)
self.assertEqual(results2, [2] * 3)
_wait() # make sure all workers settle into cond.wait()
# Notify all threads: they are all in their second wait
cond.acquire()
cond.notify_all()
Expand Down