[3.6] bpo-30595: Fix multiprocessing.Queue.get(timeout) (#2027) (#2881)

* bpo-30595: Fix multiprocessing.Queue.get(timeout) (#2027)

multiprocessing.Queue.get() with a timeout now polls its reader in
non-blocking mode if it succeeded to aquire the lock but the acquire
took longer than the timeout.

Co-Authored-By: Grzegorz Grzywacz <[email protected]>
(cherry picked from commit 1b7863c)

* bpo-30595: Increase test_queue_feeder_donot_stop_onexc() timeout (#2148)

_test_multiprocessing.test_queue_feeder_donot_stop_onexc() now uses a
timeout of 1 second on Queue.get(), instead of 0.1 second, for slow
buildbots.
(cherry picked from commit 8f6eeaf)

Author: vstinner

Lib/multiprocessing/queues.py

@@ -101,7 +101,7 @@ def get(self, block=True, timeout=None):
             try:
                 if block:
                     timeout = deadline - time.time()
-                    if timeout < 0 or not self._poll(timeout):
+                    if not self._poll(timeout):
                         raise Empty
                 elif not self._poll():
                     raise Empty

Misc/NEWS.d/next/Library/2017-07-26-04-46-12.bpo-30595.-zJ7d8.rst

@@ -0,0 +1,3 @@
+multiprocessing.Queue.get() with a timeout now polls its reader in non-
+blocking mode if it succeeded to aquire the lock but the acquire took longer
+than the timeout.