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bpo-31540: Allow passing multiprocessing context to ProcessPoolExecutor (#3682)

This commit is contained in:
Thomas Moreau 2017-10-03 11:53:17 +02:00 committed by Antoine Pitrou
parent efb560eee2
commit e8c368df22
5 changed files with 170 additions and 40 deletions
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2
.travis.yml
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@ -56,7 +56,7 @@ matrix:
./venv/bin/python -m test.pythoninfo
script:
# Skip tests that re-run the entire test suite.
- ./venv/bin/python -m coverage run --pylib -m test --fail-env-changed -uall,-cpu -x test_multiprocessing_fork -x test_multiprocessing_forkserver -x test_multiprocessing_spawn
- ./venv/bin/python -m coverage run --pylib -m test --fail-env-changed -uall,-cpu -x test_multiprocessing_fork -x test_multiprocessing_forkserver -x test_multiprocessing_spawn -x test_concurrent_futures
after_script: # Probably should be after_success once test suite updated to run under coverage.py.
# Make the `coverage` command available to Codecov w/ a version of Python that can parse all source files.
- source ./venv/bin/activate

9
Doc/library/concurrent.futures.rst
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@ -191,13 +191,16 @@ that :class:`ProcessPoolExecutor` will not work in the interactive interpreter.
Calling :class:`Executor` or :class:`Future` methods from a callable submitted
to a :class:`ProcessPoolExecutor` will result in deadlock.
.. class:: ProcessPoolExecutor(max_workers=None)
.. class:: ProcessPoolExecutor(max_workers=None, mp_context=None)
An :class:`Executor` subclass that executes calls asynchronously using a pool
of at most *max_workers* processes. If *max_workers* is ``None`` or not
given, it will default to the number of processors on the machine.
If *max_workers* is lower or equal to ``0``, then a :exc:`ValueError`
will be raised.
*mp_context* can be a multiprocessing context or None. It will be used to
launch the workers. If *mp_context* is ``None`` or not given, the default
multiprocessing context is used.
.. versionchanged:: 3.3
When one of the worker processes terminates abruptly, a
@ -205,6 +208,10 @@ to a :class:`ProcessPoolExecutor` will result in deadlock.
was undefined but operations on the executor or its futures would often
freeze or deadlock.
.. versionchanged:: 3.7
The *mp_context* argument was added to allow users to control the
start_method for worker processes created by the pool.
.. _processpoolexecutor-example:

66
Lib/concurrent/futures/process.py
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@ -50,8 +50,7 @@ import os
from concurrent.futures import _base
import queue
from queue import Full
import multiprocessing
from multiprocessing import SimpleQueue
import multiprocessing as mp
from multiprocessing.connection import wait
import threading
import weakref
@ -74,11 +73,11 @@ import traceback
# threads/processes finish.
_threads_queues = weakref.WeakKeyDictionary()
_shutdown = False
_global_shutdown = False
def _python_exit():
global _shutdown
_shutdown = True
global _global_shutdown
_global_shutdown = True
items = list(_threads_queues.items())
for t, q in items:
q.put(None)
@ -158,12 +157,10 @@ def _process_worker(call_queue, result_queue):
This worker is run in a separate process.
Args:
call_queue: A multiprocessing.Queue of _CallItems that will be read and
call_queue: A ctx.Queue of _CallItems that will be read and
evaluated by the worker.
result_queue: A multiprocessing.Queue of _ResultItems that will written
result_queue: A ctx.Queue of _ResultItems that will written
to by the worker.
shutdown: A multiprocessing.Event that will be set as a signal to the
worker that it should exit when call_queue is empty.
"""
while True:
call_item = call_queue.get(block=True)
@ -180,6 +177,11 @@ def _process_worker(call_queue, result_queue):
result_queue.put(_ResultItem(call_item.work_id,
result=r))
# Liberate the resource as soon as possible, to avoid holding onto
# open files or shared memory that is not needed anymore
del call_item
def _add_call_item_to_queue(pending_work_items,
work_ids,
call_queue):
@ -231,20 +233,21 @@ def _queue_management_worker(executor_reference,
executor_reference: A weakref.ref to the ProcessPoolExecutor that owns
this thread. Used to determine if the ProcessPoolExecutor has been
garbage collected and that this function can exit.
process: A list of the multiprocessing.Process instances used as
process: A list of the ctx.Process instances used as
workers.
pending_work_items: A dict mapping work ids to _WorkItems e.g.
{5: <_WorkItem...>, 6: <_WorkItem...>, ...}
work_ids_queue: A queue.Queue of work ids e.g. Queue([5, 6, ...]).
call_queue: A multiprocessing.Queue that will be filled with _CallItems
call_queue: A ctx.Queue that will be filled with _CallItems
derived from _WorkItems for processing by the process workers.
result_queue: A multiprocessing.Queue of _ResultItems generated by the
result_queue: A ctx.SimpleQueue of _ResultItems generated by the
process workers.
"""
executor = None
def shutting_down():
return _shutdown or executor is None or executor._shutdown_thread
return (_global_shutdown or executor is None
or executor._shutdown_thread)
def shutdown_worker():
# This is an upper bound
@ -254,7 +257,7 @@ def _queue_management_worker(executor_reference,
# Release the queue's resources as soon as possible.
call_queue.close()
# If .join() is not called on the created processes then
# some multiprocessing.Queue methods may deadlock on Mac OS X.
# some ctx.Queue methods may deadlock on Mac OS X.
for p in processes.values():
p.join()
@ -377,13 +380,15 @@ class BrokenProcessPool(RuntimeError):
class ProcessPoolExecutor(_base.Executor):
def __init__(self, max_workers=None):
def __init__(self, max_workers=None, mp_context=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.
mp_context: A multiprocessing context to launch the workers. This
object should provide SimpleQueue, Queue and Process.
"""
_check_system_limits()
@ -394,17 +399,20 @@ class ProcessPoolExecutor(_base.Executor):
raise ValueError("max_workers must be greater than 0")
self._max_workers = max_workers
if mp_context is None:
mp_context = mp.get_context()
self._mp_context = mp_context
# 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)
queue_size = self._max_workers + EXTRA_QUEUED_CALLS
self._call_queue = mp_context.Queue(queue_size)
# 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
self._result_queue = SimpleQueue()
self._result_queue = mp_context.SimpleQueue()
self._work_ids = queue.Queue()
self._queue_management_thread = None
# Map of pids to processes
@ -426,23 +434,23 @@ class ProcessPoolExecutor(_base.Executor):
# Start the processes so that their sentinels are known.
self._adjust_process_count()
self._queue_management_thread = threading.Thread(
target=_queue_management_worker,
args=(weakref.ref(self, weakref_cb),
self._processes,
self._pending_work_items,
self._work_ids,
self._call_queue,
self._result_queue))
target=_queue_management_worker,
args=(weakref.ref(self, weakref_cb),
self._processes,
self._pending_work_items,
self._work_ids,
self._call_queue,
self._result_queue))
self._queue_management_thread.daemon = True
self._queue_management_thread.start()
_threads_queues[self._queue_management_thread] = self._result_queue
def _adjust_process_count(self):
for _ in range(len(self._processes), self._max_workers):
p = multiprocessing.Process(
target=_process_worker,
args=(self._call_queue,
self._result_queue))
p = self._mp_context.Process(
target=_process_worker,
args=(self._call_queue,
self._result_queue))
p.start()
self._processes[p.pid] = p

129
Lib/test/test_concurrent_futures.py
View File

@ -19,6 +19,7 @@ from concurrent import futures
from concurrent.futures._base import (
PENDING, RUNNING, CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED, Future)
from concurrent.futures.process import BrokenProcessPool
from multiprocessing import get_context
def create_future(state=PENDING, exception=None, result=None):
@ -56,6 +57,15 @@ class MyObject(object):
pass
class EventfulGCObj():
def __init__(self, ctx):
mgr = get_context(ctx).Manager()
self.event = mgr.Event()
def __del__(self):
self.event.set()
def make_dummy_object(_):
return MyObject()
@ -77,7 +87,13 @@ class ExecutorMixin:
self.t1 = time.time()
try:
self.executor = self.executor_type(max_workers=self.worker_count)
if hasattr(self, "ctx"):
self.executor = self.executor_type(
max_workers=self.worker_count,
mp_context=get_context(self.ctx))
else:
self.executor = self.executor_type(
max_workers=self.worker_count)
except NotImplementedError as e:
self.skipTest(str(e))
self._prime_executor()
@ -107,8 +123,29 @@ class ThreadPoolMixin(ExecutorMixin):
executor_type = futures.ThreadPoolExecutor
class ProcessPoolMixin(ExecutorMixin):
class ProcessPoolForkMixin(ExecutorMixin):
executor_type = futures.ProcessPoolExecutor
ctx = "fork"
def setUp(self):
if sys.platform == "win32":
self.skipTest("require unix system")
super().setUp()
class ProcessPoolSpawnMixin(ExecutorMixin):
executor_type = futures.ProcessPoolExecutor
ctx = "spawn"
class ProcessPoolForkserverMixin(ExecutorMixin):
executor_type = futures.ProcessPoolExecutor
ctx = "forkserver"
def setUp(self):
if sys.platform == "win32":
self.skipTest("require unix system")
super().setUp()
class ExecutorShutdownTest:
@ -124,9 +161,17 @@ class ExecutorShutdownTest:
from concurrent.futures import {executor_type}
from time import sleep
from test.test_concurrent_futures import sleep_and_print
t = {executor_type}(5)
t.submit(sleep_and_print, 1.0, "apple")
""".format(executor_type=self.executor_type.__name__))
if __name__ == "__main__":
context = '{context}'
if context == "":
t = {executor_type}(5)
else:
from multiprocessing import get_context
context = get_context(context)
t = {executor_type}(5, mp_context=context)
t.submit(sleep_and_print, 1.0, "apple")
""".format(executor_type=self.executor_type.__name__,
context=getattr(self, "ctx", "")))
# Errors in atexit hooks don't change the process exit code, check
# stderr manually.
self.assertFalse(err)
@ -194,7 +239,7 @@ class ThreadPoolShutdownTest(ThreadPoolMixin, ExecutorShutdownTest, BaseTestCase
t.join()
class ProcessPoolShutdownTest(ProcessPoolMixin, ExecutorShutdownTest, BaseTestCase):
class ProcessPoolShutdownTest(ExecutorShutdownTest):
def _prime_executor(self):
pass
@ -233,6 +278,22 @@ class ProcessPoolShutdownTest(ProcessPoolMixin, ExecutorShutdownTest, BaseTestCa
call_queue.join_thread()
class ProcessPoolForkShutdownTest(ProcessPoolForkMixin, BaseTestCase,
ProcessPoolShutdownTest):
pass
class ProcessPoolForkserverShutdownTest(ProcessPoolForkserverMixin,
BaseTestCase,
ProcessPoolShutdownTest):
pass
class ProcessPoolSpawnShutdownTest(ProcessPoolSpawnMixin, BaseTestCase,
ProcessPoolShutdownTest):
pass
class WaitTests:
def test_first_completed(self):
@ -352,7 +413,17 @@ class ThreadPoolWaitTests(ThreadPoolMixin, WaitTests, BaseTestCase):
sys.setswitchinterval(oldswitchinterval)
class ProcessPoolWaitTests(ProcessPoolMixin, WaitTests, BaseTestCase):
class ProcessPoolForkWaitTests(ProcessPoolForkMixin, WaitTests, BaseTestCase):
pass
class ProcessPoolForkserverWaitTests(ProcessPoolForkserverMixin, WaitTests,
BaseTestCase):
pass
class ProcessPoolSpawnWaitTests(ProcessPoolSpawnMixin, BaseTestCase,
WaitTests):
pass
@ -440,7 +511,19 @@ class ThreadPoolAsCompletedTests(ThreadPoolMixin, AsCompletedTests, BaseTestCase
pass
class ProcessPoolAsCompletedTests(ProcessPoolMixin, AsCompletedTests, BaseTestCase):
class ProcessPoolForkAsCompletedTests(ProcessPoolForkMixin, AsCompletedTests,
BaseTestCase):
pass
class ProcessPoolForkserverAsCompletedTests(ProcessPoolForkserverMixin,
AsCompletedTests,
BaseTestCase):
pass
class ProcessPoolSpawnAsCompletedTests(ProcessPoolSpawnMixin, AsCompletedTests,
BaseTestCase):
pass
@ -540,7 +623,7 @@ class ThreadPoolExecutorTest(ThreadPoolMixin, ExecutorTest, BaseTestCase):
(os.cpu_count() or 1) * 5)
class ProcessPoolExecutorTest(ProcessPoolMixin, ExecutorTest, BaseTestCase):
class ProcessPoolExecutorTest(ExecutorTest):
def test_killed_child(self):
# When a child process is abruptly terminated, the whole pool gets
# "broken".
@ -595,6 +678,34 @@ class ProcessPoolExecutorTest(ProcessPoolMixin, ExecutorTest, BaseTestCase):
self.assertIn('raise RuntimeError(123) # some comment',
f1.getvalue())
def test_ressources_gced_in_workers(self):
# Ensure that argument for a job are correctly gc-ed after the job
# is finished
obj = EventfulGCObj(self.ctx)
future = self.executor.submit(id, obj)
future.result()
self.assertTrue(obj.event.wait(timeout=1))
class ProcessPoolForkExecutorTest(ProcessPoolForkMixin,
ProcessPoolExecutorTest,
BaseTestCase):
pass
class ProcessPoolForkserverExecutorTest(ProcessPoolForkserverMixin,
ProcessPoolExecutorTest,
BaseTestCase):
pass
class ProcessPoolSpawnExecutorTest(ProcessPoolSpawnMixin,
ProcessPoolExecutorTest,
BaseTestCase):
pass
class FutureTests(BaseTestCase):
def test_done_callback_with_result(self):

4
Misc/NEWS.d/next/Library/2017-09-22-16-02-00.bpo-31540.ybDHT5.rst Normal file
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@ -0,0 +1,4 @@
Allow passing a context object in
:class:`concurrent.futures.ProcessPoolExecutor` constructor.
Also, free job ressources in :class:`concurrent.futures.ProcessPoolExecutor`
earlier to improve memory usage when a worker waits for new jobs.