From 020af2a2bc4708215360a3793b5a1790e15d05dd Mon Sep 17 00:00:00 2001
From: Kristjan Valur Jonsson <sweskman@gmail.com>
Date: Mon, 11 Nov 2013 11:29:04 +0000
Subject: Issue #8799: Reduce timing sensitivity of condition test by
explicitly delaying the main thread so that it doesn't race ahead of the
workers.
---
Lib/test/lock_tests.py | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/Lib/test/lock_tests.py b/Lib/test/lock_tests.py
index 1a24bde..1cbcea2 100644
--- a/Lib/test/lock_tests.py
+++ b/Lib/test/lock_tests.py
@@ -418,6 +418,17 @@ class ConditionTests(BaseTestCase):
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 = []
@@ -445,6 +456,9 @@ class ConditionTests(BaseTestCase):
_wait()
self.assertEqual(results1, [(True, 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)
@@ -455,6 +469,7 @@ class ConditionTests(BaseTestCase):
_wait()
self.assertEqual(results1, [(True, 1)] * 3 + [(True, 2)] * 2)
self.assertEqual(results2, [(True, 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()
--
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