multiprocessing.queues.Queue leaks pipes under certain conditions (CPython issue42752)
In writing a test for #3365 I noticed there's a bit of a problem with multiprocessor.queues.Queue. The trouble is if you don't actually put anything in the Queue (say for instance you're only using it to receive in the main process) the close method won't actually lead to the write pipe closing. Since the Queue is buffer and uses a thread, the closing of the write pipe is not exactly trivial. Branch py3_7_mp_queue_close_fix is my suggested fix.