2010-09-18 19:35:02 -03:00
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# Copyright 2009 Brian Quinlan. All Rights Reserved.
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# Licensed to PSF under a Contributor Agreement.
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"""Implements ProcessPoolExecutor.
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The follow diagram and text describe the data-flow through the system:
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|======================= In-process =====================|== Out-of-process ==|
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+----------+ +----------+ +--------+ +-----------+ +---------+
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| | => | Work Ids | => | | => | Call Q | => | |
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| | +----------+ | | +-----------+ | |
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| | | ... | | | | ... | | |
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| | | 6 | | | | 5, call() | | |
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| | | 7 | | | | ... | | |
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| Process | | ... | | Local | +-----------+ | Process |
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| Pool | +----------+ | Worker | | #1..n |
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| Executor | | Thread | | |
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| | +----------- + | | +-----------+ | |
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| | <=> | Work Items | <=> | | <= | Result Q | <= | |
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| | +------------+ | | +-----------+ | |
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| | | 6: call() | | | | ... | | |
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| | | future | | | | 4, result | | |
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| | | ... | | | | 3, except | | |
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+----------+ +------------+ +--------+ +-----------+ +---------+
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Executor.submit() called:
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- creates a uniquely numbered _WorkItem and adds it to the "Work Items" dict
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- adds the id of the _WorkItem to the "Work Ids" queue
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Local worker thread:
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- reads work ids from the "Work Ids" queue and looks up the corresponding
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WorkItem from the "Work Items" dict: if the work item has been cancelled then
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it is simply removed from the dict, otherwise it is repackaged as a
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_CallItem and put in the "Call Q". New _CallItems are put in the "Call Q"
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until "Call Q" is full. NOTE: the size of the "Call Q" is kept small because
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calls placed in the "Call Q" can no longer be cancelled with Future.cancel().
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- reads _ResultItems from "Result Q", updates the future stored in the
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"Work Items" dict and deletes the dict entry
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Process #1..n:
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- reads _CallItems from "Call Q", executes the calls, and puts the resulting
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2012-10-20 09:16:49 -03:00
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_ResultItems in "Result Q"
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2010-09-18 19:35:02 -03:00
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"""
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__author__ = 'Brian Quinlan (brian@sweetapp.com)'
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import atexit
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2011-06-08 12:21:55 -03:00
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import os
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2010-09-18 19:35:02 -03:00
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from concurrent.futures import _base
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import queue
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2013-10-16 13:06:22 -03:00
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from queue import Full
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2010-09-18 19:35:02 -03:00
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import multiprocessing
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2013-10-16 13:06:22 -03:00
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from multiprocessing import SimpleQueue
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2012-03-05 14:28:37 -04:00
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from multiprocessing.connection import wait
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2010-09-18 19:35:02 -03:00
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import threading
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import weakref
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2014-10-04 15:20:10 -03:00
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from functools import partial
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import itertools
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2015-01-17 15:02:14 -04:00
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import traceback
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2010-09-18 19:35:02 -03:00
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# Workers are created as daemon threads and processes. This is done to allow the
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# interpreter to exit when there are still idle processes in a
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# ProcessPoolExecutor's process pool (i.e. shutdown() was not called). However,
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# allowing workers to die with the interpreter has two undesirable properties:
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2016-08-30 14:47:49 -03:00
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# - The workers would still be running during interpreter shutdown,
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2010-09-18 19:35:02 -03:00
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# meaning that they would fail in unpredictable ways.
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# - The workers could be killed while evaluating a work item, which could
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# be bad if the callable being evaluated has external side-effects e.g.
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# writing to a file.
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#
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# To work around this problem, an exit handler is installed which tells the
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# workers to exit when their work queues are empty and then waits until the
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# threads/processes finish.
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2011-03-26 15:29:44 -03:00
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_threads_queues = weakref.WeakKeyDictionary()
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2010-09-18 19:35:02 -03:00
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_shutdown = False
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def _python_exit():
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global _shutdown
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_shutdown = True
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items = list(_threads_queues.items())
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for t, q in items:
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q.put(None)
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for t, q in items:
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t.join()
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2010-09-18 19:35:02 -03:00
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# Controls how many more calls than processes will be queued in the call queue.
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# A smaller number will mean that processes spend more time idle waiting for
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# work while a larger number will make Future.cancel() succeed less frequently
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# (Futures in the call queue cannot be cancelled).
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EXTRA_QUEUED_CALLS = 1
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2015-01-17 15:02:14 -04:00
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# Hack to embed stringification of remote traceback in local traceback
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class _RemoteTraceback(Exception):
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def __init__(self, tb):
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self.tb = tb
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def __str__(self):
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return self.tb
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class _ExceptionWithTraceback:
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def __init__(self, exc, tb):
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tb = traceback.format_exception(type(exc), exc, tb)
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tb = ''.join(tb)
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self.exc = exc
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self.tb = '\n"""\n%s"""' % tb
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def __reduce__(self):
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return _rebuild_exc, (self.exc, self.tb)
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def _rebuild_exc(exc, tb):
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exc.__cause__ = _RemoteTraceback(tb)
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return exc
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2010-09-18 19:35:02 -03:00
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class _WorkItem(object):
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def __init__(self, future, fn, args, kwargs):
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self.future = future
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self.fn = fn
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self.args = args
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self.kwargs = kwargs
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class _ResultItem(object):
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def __init__(self, work_id, exception=None, result=None):
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self.work_id = work_id
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self.exception = exception
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self.result = result
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class _CallItem(object):
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def __init__(self, work_id, fn, args, kwargs):
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self.work_id = work_id
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self.fn = fn
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self.args = args
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self.kwargs = kwargs
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2014-10-04 15:20:10 -03:00
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def _get_chunks(*iterables, chunksize):
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""" Iterates over zip()ed iterables in chunks. """
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it = zip(*iterables)
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while True:
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chunk = tuple(itertools.islice(it, chunksize))
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if not chunk:
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return
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yield chunk
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def _process_chunk(fn, chunk):
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""" Processes a chunk of an iterable passed to map.
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Runs the function passed to map() on a chunk of the
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iterable passed to map.
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This function is run in a separate process.
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"""
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return [fn(*args) for args in chunk]
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2011-04-12 12:48:46 -03:00
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def _process_worker(call_queue, result_queue):
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2010-09-18 19:35:02 -03:00
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"""Evaluates calls from call_queue and places the results in result_queue.
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2010-12-09 14:08:43 -04:00
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This worker is run in a separate process.
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2010-09-18 19:35:02 -03:00
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Args:
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call_queue: A multiprocessing.Queue of _CallItems that will be read and
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evaluated by the worker.
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result_queue: A multiprocessing.Queue of _ResultItems that will written
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to by the worker.
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shutdown: A multiprocessing.Event that will be set as a signal to the
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worker that it should exit when call_queue is empty.
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"""
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while True:
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2011-04-12 12:48:46 -03:00
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call_item = call_queue.get(block=True)
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if call_item is None:
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# Wake up queue management thread
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2011-06-08 12:21:55 -03:00
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result_queue.put(os.getpid())
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2011-04-12 12:48:46 -03:00
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return
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2010-09-18 19:35:02 -03:00
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try:
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2011-04-12 12:48:46 -03:00
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r = call_item.fn(*call_item.args, **call_item.kwargs)
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except BaseException as e:
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exc = _ExceptionWithTraceback(e, e.__traceback__)
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result_queue.put(_ResultItem(call_item.work_id, exception=exc))
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2010-09-18 19:35:02 -03:00
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else:
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2011-04-12 12:48:46 -03:00
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result_queue.put(_ResultItem(call_item.work_id,
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result=r))
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2010-09-18 19:35:02 -03:00
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def _add_call_item_to_queue(pending_work_items,
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work_ids,
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call_queue):
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"""Fills call_queue with _WorkItems from pending_work_items.
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This function never blocks.
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Args:
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pending_work_items: A dict mapping work ids to _WorkItems e.g.
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{5: <_WorkItem...>, 6: <_WorkItem...>, ...}
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work_ids: A queue.Queue of work ids e.g. Queue([5, 6, ...]). Work ids
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are consumed and the corresponding _WorkItems from
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pending_work_items are transformed into _CallItems and put in
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call_queue.
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call_queue: A multiprocessing.Queue that will be filled with _CallItems
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derived from _WorkItems.
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"""
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while True:
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if call_queue.full():
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return
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try:
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work_id = work_ids.get(block=False)
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except queue.Empty:
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return
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else:
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work_item = pending_work_items[work_id]
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if work_item.future.set_running_or_notify_cancel():
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call_queue.put(_CallItem(work_id,
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work_item.fn,
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work_item.args,
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work_item.kwargs),
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block=True)
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else:
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del pending_work_items[work_id]
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continue
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2011-05-03 11:34:42 -03:00
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def _queue_management_worker(executor_reference,
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processes,
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pending_work_items,
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work_ids_queue,
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call_queue,
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result_queue):
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2010-09-18 19:35:02 -03:00
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"""Manages the communication between this process and the worker processes.
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This function is run in a local thread.
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Args:
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executor_reference: A weakref.ref to the ProcessPoolExecutor that owns
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this thread. Used to determine if the ProcessPoolExecutor has been
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garbage collected and that this function can exit.
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process: A list of the multiprocessing.Process instances used as
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workers.
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pending_work_items: A dict mapping work ids to _WorkItems e.g.
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{5: <_WorkItem...>, 6: <_WorkItem...>, ...}
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work_ids_queue: A queue.Queue of work ids e.g. Queue([5, 6, ...]).
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call_queue: A multiprocessing.Queue that will be filled with _CallItems
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derived from _WorkItems for processing by the process workers.
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result_queue: A multiprocessing.Queue of _ResultItems generated by the
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process workers.
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"""
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2011-07-02 16:20:25 -03:00
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executor = None
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def shutting_down():
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return _shutdown or executor is None or executor._shutdown_thread
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2011-06-08 12:21:55 -03:00
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def shutdown_worker():
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# This is an upper bound
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nb_children_alive = sum(p.is_alive() for p in processes.values())
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for i in range(0, nb_children_alive):
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2011-07-03 08:17:06 -03:00
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call_queue.put_nowait(None)
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2011-07-15 20:51:58 -03:00
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# Release the queue's resources as soon as possible.
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call_queue.close()
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2011-06-08 12:21:55 -03:00
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# If .join() is not called on the created processes then
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2011-07-02 16:20:25 -03:00
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# some multiprocessing.Queue methods may deadlock on Mac OS X.
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2011-06-08 12:21:55 -03:00
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for p in processes.values():
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p.join()
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2012-03-05 14:28:37 -04:00
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reader = result_queue._reader
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2010-09-18 19:35:02 -03:00
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while True:
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_add_call_item_to_queue(pending_work_items,
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work_ids_queue,
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call_queue)
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2011-06-08 12:21:55 -03:00
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sentinels = [p.sentinel for p in processes.values()]
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assert sentinels
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2012-03-05 14:28:37 -04:00
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ready = wait([reader] + sentinels)
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if reader in ready:
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result_item = reader.recv()
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else:
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2011-06-08 12:21:55 -03:00
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# Mark the process pool broken so that submits fail right now.
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executor = executor_reference()
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if executor is not None:
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executor._broken = True
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executor._shutdown_thread = True
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2011-07-02 16:20:25 -03:00
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executor = None
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2011-06-08 12:21:55 -03:00
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# All futures in flight must be marked failed
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for work_id, work_item in pending_work_items.items():
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work_item.future.set_exception(
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BrokenProcessPool(
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"A process in the process pool was "
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"terminated abruptly while the future was "
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"running or pending."
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))
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2012-11-03 10:36:01 -03:00
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# Delete references to object. See issue16284
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del work_item
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2011-06-08 12:21:55 -03:00
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pending_work_items.clear()
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# Terminate remaining workers forcibly: the queues or their
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# locks may be in a dirty state and block forever.
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for p in processes.values():
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p.terminate()
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2011-07-15 20:51:58 -03:00
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shutdown_worker()
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2011-06-08 12:21:55 -03:00
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return
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if isinstance(result_item, int):
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# Clean shutdown of a worker using its PID
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# (avoids marking the executor broken)
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2011-07-02 16:20:25 -03:00
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assert shutting_down()
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2011-07-15 20:13:34 -03:00
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p = processes.pop(result_item)
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p.join()
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2011-07-02 16:20:25 -03:00
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if not processes:
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shutdown_worker()
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return
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2011-06-08 12:21:55 -03:00
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elif result_item is not None:
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work_item = pending_work_items.pop(result_item.work_id, None)
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# work_item can be None if another process terminated (see above)
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if work_item is not None:
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if result_item.exception:
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work_item.future.set_exception(result_item.exception)
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else:
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work_item.future.set_result(result_item.result)
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2012-11-03 10:36:01 -03:00
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# Delete references to object. See issue16284
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del work_item
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2011-06-08 12:21:55 -03:00
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# Check whether we should start shutting down.
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2011-03-26 15:29:44 -03:00
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executor = executor_reference()
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# No more work items can be added if:
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# - The interpreter is shutting down OR
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# - The executor that owns this worker has been collected OR
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# - The executor that owns this worker has been shutdown.
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2011-07-02 16:20:25 -03:00
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if shutting_down():
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try:
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2011-07-03 08:17:06 -03:00
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# Since no new work items can be added, it is safe to shutdown
|
|
|
|
# this thread if there are no pending work items.
|
|
|
|
if not pending_work_items:
|
|
|
|
shutdown_worker()
|
|
|
|
return
|
2011-07-02 16:20:25 -03:00
|
|
|
except Full:
|
|
|
|
# This is not a problem: we will eventually be woken up (in
|
2011-07-03 08:17:06 -03:00
|
|
|
# result_queue.get()) and be able to send a sentinel again.
|
2011-07-02 16:20:25 -03:00
|
|
|
pass
|
|
|
|
executor = None
|
2010-09-18 19:35:02 -03:00
|
|
|
|
2011-01-02 20:07:01 -04:00
|
|
|
_system_limits_checked = False
|
|
|
|
_system_limited = None
|
|
|
|
def _check_system_limits():
|
|
|
|
global _system_limits_checked, _system_limited
|
|
|
|
if _system_limits_checked:
|
|
|
|
if _system_limited:
|
|
|
|
raise NotImplementedError(_system_limited)
|
|
|
|
_system_limits_checked = True
|
|
|
|
try:
|
|
|
|
nsems_max = os.sysconf("SC_SEM_NSEMS_MAX")
|
|
|
|
except (AttributeError, ValueError):
|
|
|
|
# sysconf not available or setting not available
|
|
|
|
return
|
|
|
|
if nsems_max == -1:
|
2013-08-17 10:11:40 -03:00
|
|
|
# indetermined limit, assume that limit is determined
|
2011-01-02 20:07:01 -04:00
|
|
|
# by available memory only
|
|
|
|
return
|
|
|
|
if nsems_max >= 256:
|
|
|
|
# minimum number of semaphores available
|
|
|
|
# according to POSIX
|
|
|
|
return
|
|
|
|
_system_limited = "system provides too few semaphores (%d available, 256 necessary)" % nsems_max
|
|
|
|
raise NotImplementedError(_system_limited)
|
|
|
|
|
2011-06-08 12:21:55 -03:00
|
|
|
|
|
|
|
class BrokenProcessPool(RuntimeError):
|
|
|
|
"""
|
|
|
|
Raised when a process in a ProcessPoolExecutor terminated abruptly
|
|
|
|
while a future was in the running state.
|
|
|
|
"""
|
|
|
|
|
|
|
|
|
2010-09-18 19:35:02 -03:00
|
|
|
class ProcessPoolExecutor(_base.Executor):
|
|
|
|
def __init__(self, max_workers=None):
|
|
|
|
"""Initializes a new ProcessPoolExecutor instance.
|
|
|
|
|
|
|
|
Args:
|
|
|
|
max_workers: The maximum number of processes that can be used to
|
|
|
|
execute the given calls. If None or not given then as many
|
|
|
|
worker processes will be created as the machine has processors.
|
|
|
|
"""
|
2011-01-02 20:07:01 -04:00
|
|
|
_check_system_limits()
|
2010-09-18 19:35:02 -03:00
|
|
|
|
|
|
|
if max_workers is None:
|
2013-06-28 14:25:45 -03:00
|
|
|
self._max_workers = os.cpu_count() or 1
|
2010-09-18 19:35:02 -03:00
|
|
|
else:
|
2014-05-17 17:51:10 -03:00
|
|
|
if max_workers <= 0:
|
|
|
|
raise ValueError("max_workers must be greater than 0")
|
|
|
|
|
2010-09-18 19:35:02 -03:00
|
|
|
self._max_workers = max_workers
|
|
|
|
|
|
|
|
# Make the call queue slightly larger than the number of processes to
|
|
|
|
# prevent the worker processes from idling. But don't make it too big
|
|
|
|
# because futures in the call queue cannot be cancelled.
|
|
|
|
self._call_queue = multiprocessing.Queue(self._max_workers +
|
|
|
|
EXTRA_QUEUED_CALLS)
|
2011-07-15 20:51:58 -03:00
|
|
|
# Killed worker processes can produce spurious "broken pipe"
|
|
|
|
# tracebacks in the queue's own worker thread. But we detect killed
|
|
|
|
# processes anyway, so silence the tracebacks.
|
|
|
|
self._call_queue._ignore_epipe = True
|
2011-04-12 12:58:11 -03:00
|
|
|
self._result_queue = SimpleQueue()
|
2010-09-18 19:35:02 -03:00
|
|
|
self._work_ids = queue.Queue()
|
|
|
|
self._queue_management_thread = None
|
2011-06-08 12:21:55 -03:00
|
|
|
# Map of pids to processes
|
|
|
|
self._processes = {}
|
2010-09-18 19:35:02 -03:00
|
|
|
|
|
|
|
# Shutdown is a two-step process.
|
|
|
|
self._shutdown_thread = False
|
|
|
|
self._shutdown_lock = threading.Lock()
|
2011-06-08 12:21:55 -03:00
|
|
|
self._broken = False
|
2010-09-18 19:35:02 -03:00
|
|
|
self._queue_count = 0
|
|
|
|
self._pending_work_items = {}
|
|
|
|
|
|
|
|
def _start_queue_management_thread(self):
|
2011-03-26 15:29:44 -03:00
|
|
|
# When the executor gets lost, the weakref callback will wake up
|
|
|
|
# the queue management thread.
|
|
|
|
def weakref_cb(_, q=self._result_queue):
|
|
|
|
q.put(None)
|
2010-09-18 19:35:02 -03:00
|
|
|
if self._queue_management_thread is None:
|
2011-06-08 12:21:55 -03:00
|
|
|
# Start the processes so that their sentinels are known.
|
|
|
|
self._adjust_process_count()
|
2010-09-18 19:35:02 -03:00
|
|
|
self._queue_management_thread = threading.Thread(
|
2011-05-03 11:34:42 -03:00
|
|
|
target=_queue_management_worker,
|
2011-03-26 15:29:44 -03:00
|
|
|
args=(weakref.ref(self, weakref_cb),
|
2010-09-18 19:35:02 -03:00
|
|
|
self._processes,
|
|
|
|
self._pending_work_items,
|
|
|
|
self._work_ids,
|
|
|
|
self._call_queue,
|
2011-04-12 12:48:46 -03:00
|
|
|
self._result_queue))
|
2010-09-18 19:35:02 -03:00
|
|
|
self._queue_management_thread.daemon = True
|
|
|
|
self._queue_management_thread.start()
|
2011-03-26 15:29:44 -03:00
|
|
|
_threads_queues[self._queue_management_thread] = self._result_queue
|
2010-09-18 19:35:02 -03:00
|
|
|
|
|
|
|
def _adjust_process_count(self):
|
|
|
|
for _ in range(len(self._processes), self._max_workers):
|
|
|
|
p = multiprocessing.Process(
|
|
|
|
target=_process_worker,
|
|
|
|
args=(self._call_queue,
|
2011-04-12 12:48:46 -03:00
|
|
|
self._result_queue))
|
2010-09-18 19:35:02 -03:00
|
|
|
p.start()
|
2011-06-08 12:21:55 -03:00
|
|
|
self._processes[p.pid] = p
|
2010-09-18 19:35:02 -03:00
|
|
|
|
|
|
|
def submit(self, fn, *args, **kwargs):
|
|
|
|
with self._shutdown_lock:
|
2011-06-08 12:21:55 -03:00
|
|
|
if self._broken:
|
|
|
|
raise BrokenProcessPool('A child process terminated '
|
|
|
|
'abruptly, the process pool is not usable anymore')
|
2010-09-18 19:35:02 -03:00
|
|
|
if self._shutdown_thread:
|
|
|
|
raise RuntimeError('cannot schedule new futures after shutdown')
|
|
|
|
|
|
|
|
f = _base.Future()
|
|
|
|
w = _WorkItem(f, fn, args, kwargs)
|
|
|
|
|
|
|
|
self._pending_work_items[self._queue_count] = w
|
|
|
|
self._work_ids.put(self._queue_count)
|
|
|
|
self._queue_count += 1
|
2011-03-26 15:29:44 -03:00
|
|
|
# Wake up queue management thread
|
|
|
|
self._result_queue.put(None)
|
2010-09-18 19:35:02 -03:00
|
|
|
|
|
|
|
self._start_queue_management_thread()
|
|
|
|
return f
|
|
|
|
submit.__doc__ = _base.Executor.submit.__doc__
|
|
|
|
|
2014-10-04 15:20:10 -03:00
|
|
|
def map(self, fn, *iterables, timeout=None, chunksize=1):
|
2015-11-02 00:20:33 -04:00
|
|
|
"""Returns an iterator equivalent to map(fn, iter).
|
2014-10-04 15:20:10 -03:00
|
|
|
|
|
|
|
Args:
|
|
|
|
fn: A callable that will take as many arguments as there are
|
|
|
|
passed iterables.
|
|
|
|
timeout: The maximum number of seconds to wait. If None, then there
|
|
|
|
is no limit on the wait time.
|
|
|
|
chunksize: If greater than one, the iterables will be chopped into
|
|
|
|
chunks of size chunksize and submitted to the process pool.
|
|
|
|
If set to one, the items in the list will be sent one at a time.
|
|
|
|
|
|
|
|
Returns:
|
|
|
|
An iterator equivalent to: map(func, *iterables) but the calls may
|
|
|
|
be evaluated out-of-order.
|
|
|
|
|
|
|
|
Raises:
|
|
|
|
TimeoutError: If the entire result iterator could not be generated
|
|
|
|
before the given timeout.
|
|
|
|
Exception: If fn(*args) raises for any values.
|
|
|
|
"""
|
|
|
|
if chunksize < 1:
|
|
|
|
raise ValueError("chunksize must be >= 1.")
|
|
|
|
|
|
|
|
results = super().map(partial(_process_chunk, fn),
|
|
|
|
_get_chunks(*iterables, chunksize=chunksize),
|
|
|
|
timeout=timeout)
|
|
|
|
return itertools.chain.from_iterable(results)
|
|
|
|
|
2010-09-18 19:35:02 -03:00
|
|
|
def shutdown(self, wait=True):
|
|
|
|
with self._shutdown_lock:
|
|
|
|
self._shutdown_thread = True
|
2011-03-26 15:29:44 -03:00
|
|
|
if self._queue_management_thread:
|
|
|
|
# Wake up queue management thread
|
|
|
|
self._result_queue.put(None)
|
|
|
|
if wait:
|
2010-09-18 19:35:02 -03:00
|
|
|
self._queue_management_thread.join()
|
2013-08-17 10:11:40 -03:00
|
|
|
# To reduce the risk of opening too many files, remove references to
|
2010-09-18 19:35:02 -03:00
|
|
|
# objects that use file descriptors.
|
|
|
|
self._queue_management_thread = None
|
|
|
|
self._call_queue = None
|
|
|
|
self._result_queue = None
|
|
|
|
self._processes = None
|
|
|
|
shutdown.__doc__ = _base.Executor.shutdown.__doc__
|
|
|
|
|
|
|
|
atexit.register(_python_exit)
|