[3.7]bpo-29341: Backport b942707 3.7

[BNMetrics]

manual backport for https://bugs.python.org/issue29341

https://bugs.python.org/issue29341

[bedevere-bot]

@pablogsal: Please replace # with GH- in the commit message next time. Thanks!

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 FreeBSD 10-STABLE Non-Debug 3.7 has failed when building commit 08026b1.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/170/builds/75) and take a look at the build logs.
4. Check if the failure is related to this commit (08026b1) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/170/builds/75

Click to see traceback logs

Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.7.koobs-freebsd10.nondebug/build/Lib/multiprocessing/process.py", line 297, in _bootstrap
    self.run()
  File "/usr/home/buildbot/python/3.7.koobs-freebsd10.nondebug/build/Lib/multiprocessing/process.py", line 99, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/home/buildbot/python/3.7.koobs-freebsd10.nondebug/build/Lib/test/_test_multiprocessing.py", line 2861, in _echo
    conn.send_bytes(msg)
  File "/usr/home/buildbot/python/3.7.koobs-freebsd10.nondebug/build/Lib/multiprocessing/connection.py", line 200, in send_bytes
    self._send_bytes(m[offset:offset + size])
  File "/usr/home/buildbot/python/3.7.koobs-freebsd10.nondebug/build/Lib/multiprocessing/connection.py", line 404, in _send_bytes
    self._send(header + buf)
  File "/usr/home/buildbot/python/3.7.koobs-freebsd10.nondebug/build/Lib/multiprocessing/connection.py", line 368, in _send
    n = write(self._handle, buf)
BrokenPipeError: [Errno 32] Broken pipe


Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.7.koobs-freebsd10.nondebug/build/Lib/test/_test_multiprocessing.py", line 2923, in test_connection
    self.assertEqual(poll(TIMEOUT1), True)
AssertionError: False != True

----------------------------------------------------------------------

Ran 315 tests in 209.191s

FAILED (failures=1, skipped=27)