> See also bpo-30966 "Add multiprocessing.SimpleQueue.close()".

I pushed a commit 1a275013d1ecc2e3778d64fda86174b2f13d6969: 
"Process.shutdown(wait=True) of concurrent.futures now closes
explicitly the result queue."

test_shutdown_deadlock_pickle() still rely on the queue to be closed implicitly. Queue created at:

  (...)
  File "/home/vstinner/python/master/Lib/test/test_concurrent_futures.py", lineno 1196
    with self.executor_type(max_workers=2,
  File "/home/vstinner/python/master/Lib/concurrent/futures/process.py", lineno 637
    self._result_queue = mp_context.SimpleQueue()
  File "/home/vstinner/python/master/Lib/multiprocessing/context.py", lineno 113
    return SimpleQueue(ctx=self.get_context())
  File "/home/vstinner/python/master/Lib/multiprocessing/queues.py", lineno 341
    self._reader, self._writer = connection.Pipe(duplex=False)
  File "/home/vstinner/python/master/Lib/multiprocessing/connection.py", lineno 539
    c2 = Connection(fd2, readable=False)