Billiard

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- Fixed problem with Python3 and setblocking.

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- Now works on Windows again.

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- ApplyResult.terminate() may be set to signify that the job
must not be executed. It can be used in combination with
Pool.terminate_job.

- Pipe/_SimpleQueue: Now supports rnonblock/wnonblock arguments
to set the read or write end of the pipe to be nonblocking.

- Pool: Log message included exception info but exception happened
in another process so the resulting traceback was wrong.

- Pool: Worker process can now prepare results before they are sent
back to the main process (using ``Worker.prepare_result``).

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- Pool: New ``correlation_id`` argument to ``apply_async`` can be
used to set a related id for the ``ApplyResult`` object returned:

>>> r = pool.apply_async(target, args, kwargs, correlation_id='foo')
>>> r.correlation_id
'foo'

- Pool: New callback `on_process_exit` is called when a pool
process exits, with signature ``(pid, exitcode)``.

Contributed by Daniel M. Taub.

- Pool: Improved the too many restarts detection.

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- Dual code base now runs on Python 2.6+ and Python 3.

- No longer compatible with Python 2.5

- Includes many changes from multiprocessing in 3.4.

- Now uses ``time.monotonic`` when available, also including
fallback implementations for Linux and macOS.

- No longer cleans up after receiving SIGILL, SIGSEGV or SIGFPE

Contributed by Kevin Blackham

- ``Finalize`` and ``register_after_fork`` is now aliases to multiprocessing.

It's better to import these from multiprocessing directly now
so that there aren't multiple registries.

- New `billiard.queues._SimpleQueue` that does not use semaphores.

- Pool: Can now be extended to support using multiple IPC queues.

- Pool: Can now use async I/O to write to pool IPC queues.

- Pool: New ``Worker.on_loop_stop`` handler can be used to add actions
at pool worker process shutdown.

Note that, like all finalization handlers, there is no guarantee that
this will be executed.

Contributed by dmtaub.

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- Fixed ImportError in billiard._ext