test_put() of test_multiprocessing queue tests has a race condition

[vstinner]

BPO	32090
Nosy	@vstinner

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2018-05-29.21:54:56.259>
created_at = <Date 2017-11-20.15:32:21.236>
labels = ['3.7', 'tests']
title = 'test_put() of test_multiprocessing queue tests has a race condition'
updated_at = <Date 2018-05-29.21:54:56.259>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2018-05-29.21:54:56.259>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2018-05-29.21:54:56.259>
closer = 'vstinner'
components = ['Tests']
creation = <Date 2017-11-20.15:32:21.236>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 32090
keywords = []
message_count = 2.0
messages = ['306553', '318108']
nosy_count = 1.0
nosy_names = ['vstinner']
pr_nums = []
priority = 'normal'
resolution = 'out of date'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue32090'
versions = ['Python 3.7']

[vstinner]

The test failed on AMD64 FreeBSD 10.x Shared 3.x:

http://buildbot.python.org/all/#/builders/87/builds/200/steps/4/logs/stdio

FAIL: test_put (test.test_multiprocessing_fork.WithProcessesTestQueue)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.x.koobs-freebsd10/build/Lib/test/_test_multiprocessing.py", line 809, in test_put
    self.assertEqual(queue_empty(queue), False)
AssertionError: True != False

--

I succeeded to reproduce the issue on Linux with this change:

diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py
index dbca2d89ed..0754ac0d52 100644
--- a/Lib/test/_test_multiprocessing.py
+++ b/Lib/test/_test_multiprocessing.py
@@ -804,7 +804,7 @@ class _TestQueue(BaseTestCase):
         queue.put_nowait(6)
 
         # the values may be in buffer but not yet in pipe so sleep a bit
-        time.sleep(DELTA)
+        time.sleep(0)
 
         self.assertEqual(queue_empty(queue), False)
         self.assertEqual(queue_full(queue, MAXSIZE), True)

[vstinner]

I didn't see this failure recently, and I'm no longer able to reproduce the issue on Linux.