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bpo-21423: Add an initializer argument to {Process,Thread}PoolExecutor (#4241) 

* bpo-21423: Add an initializer argument to {Process,Thread}PoolExecutor

* Fix docstring
This commit is contained in:
Antoine Pitrou 2017-11-04 11:05:49 +01:00 committed by GitHub
parent b838cc3ff4
commit 63ff4131af
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7 changed files with 246 additions and 81 deletions
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48
Doc/library/concurrent.futures.rst
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@ -124,11 +124,17 @@ And::
executor.submit(wait_on_future)
.. class:: ThreadPoolExecutor(max_workers=None, thread_name_prefix='')
.. class:: ThreadPoolExecutor(max_workers=None, thread_name_prefix='', initializer=None, initargs=())
An :class:`Executor` subclass that uses a pool of at most *max_workers*
threads to execute calls asynchronously.
*initializer* is an optional callable that is called at the start of
each worker thread; *initargs* is a tuple of arguments passed to the
initializer. Should *initializer* raise an exception, all currently
pending jobs will raise a :exc:`~concurrent.futures.thread.BrokenThreadPool`,
as well any attempt to submit more jobs to the pool.
.. versionchanged:: 3.5
If *max_workers* is ``None`` or
not given, it will default to the number of processors on the machine,
@ -142,6 +148,10 @@ And::
control the threading.Thread names for worker threads created by
the pool for easier debugging.
.. versionchanged:: 3.7
Added the *initializer* and *initargs* arguments.
.. _threadpoolexecutor-example:
ThreadPoolExecutor Example
@ -191,7 +201,7 @@ 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, mp_context=None)
.. class:: ProcessPoolExecutor(max_workers=None, mp_context=None, initializer=None, initargs=())
An :class:`Executor` subclass that executes calls asynchronously using a pool
of at most *max_workers* processes. If *max_workers* is ``None`` or not
@ -202,6 +212,12 @@ to a :class:`ProcessPoolExecutor` will result in deadlock.
launch the workers. If *mp_context* is ``None`` or not given, the default
multiprocessing context is used.
*initializer* is an optional callable that is called at the start of
each worker process; *initargs* is a tuple of arguments passed to the
initializer. Should *initializer* raise an exception, all currently
pending jobs will raise a :exc:`~concurrent.futures.thread.BrokenThreadPool`,
as well any attempt to submit more jobs to the pool.
.. versionchanged:: 3.3
When one of the worker processes terminates abruptly, a
:exc:`BrokenProcessPool` error is now raised. Previously, behaviour
@ -212,6 +228,8 @@ to a :class:`ProcessPoolExecutor` will result in deadlock.
The *mp_context* argument was added to allow users to control the
start_method for worker processes created by the pool.
Added the *initializer* and *initargs* arguments.
.. _processpoolexecutor-example:
@ -432,13 +450,31 @@ Exception classes
Raised when a future operation exceeds the given timeout.
.. exception:: BrokenExecutor
Derived from :exc:`RuntimeError`, this exception class is raised
when an executor is broken for some reason, and cannot be used
to submit or execute new tasks.
.. versionadded:: 3.7
.. currentmodule:: concurrent.futures.thread
.. exception:: BrokenThreadPool
Derived from :exc:`~concurrent.futures.BrokenExecutor`, this exception
class is raised when one of the workers of a :class:`ThreadPoolExecutor`
has failed initializing.
.. versionadded:: 3.7
.. currentmodule:: concurrent.futures.process
.. exception:: BrokenProcessPool
Derived from :exc:`RuntimeError`, this exception class is raised when
one of the workers of a :class:`ProcessPoolExecutor` has terminated
in a non-clean fashion (for example, if it was killed from the outside).
Derived from :exc:`~concurrent.futures.BrokenExecutor` (formerly
:exc:`RuntimeError`), this exception class is raised when one of the
workers of a :class:`ProcessPoolExecutor` has terminated in a non-clean
fashion (for example, if it was killed from the outside).
.. versionadded:: 3.3

1
Lib/concurrent/futures/__init__.py
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@ -10,6 +10,7 @@ from concurrent.futures._base import (FIRST_COMPLETED,
ALL_COMPLETED,
CancelledError,
TimeoutError,
BrokenExecutor,
Future,
Executor,
wait,

6
Lib/concurrent/futures/_base.py
View File

@ -610,3 +610,9 @@ class Executor(object):
def __exit__(self, exc_type, exc_val, exc_tb):
self.shutdown(wait=True)
return False
class BrokenExecutor(RuntimeError):
"""
Raised when a executor has become non-functional after a severe failure.
"""

36
Lib/concurrent/futures/process.py
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@ -131,6 +131,7 @@ class _CallItem(object):
self.args = args
self.kwargs = kwargs
def _get_chunks(*iterables, chunksize):
""" Iterates over zip()ed iterables in chunks. """
it = zip(*iterables)
@ -151,7 +152,7 @@ def _process_chunk(fn, chunk):
"""
return [fn(*args) for args in chunk]
def _process_worker(call_queue, result_queue):
def _process_worker(call_queue, result_queue, initializer, initargs):
"""Evaluates calls from call_queue and places the results in result_queue.
This worker is run in a separate process.
@ -161,7 +162,17 @@ def _process_worker(call_queue, result_queue):
evaluated by the worker.
result_queue: A ctx.Queue of _ResultItems that will written
to by the worker.
initializer: A callable initializer, or None
initargs: A tuple of args for the initializer
"""
if initializer is not None:
try:
initializer(*initargs)
except BaseException:
_base.LOGGER.critical('Exception in initializer:', exc_info=True)
# The parent will notice that the process stopped and
# mark the pool broken
return
while True:
call_item = call_queue.get(block=True)
if call_item is None:
@ -277,7 +288,9 @@ def _queue_management_worker(executor_reference,
# Mark the process pool broken so that submits fail right now.
executor = executor_reference()
if executor is not None:
executor._broken = True
executor._broken = ('A child process terminated '
'abruptly, the process pool is not '
'usable anymore')
executor._shutdown_thread = True
executor = None
# All futures in flight must be marked failed
@ -372,7 +385,7 @@ def _chain_from_iterable_of_lists(iterable):
yield element.pop()
class BrokenProcessPool(RuntimeError):
class BrokenProcessPool(_base.BrokenExecutor):
"""
Raised when a process in a ProcessPoolExecutor terminated abruptly
while a future was in the running state.
@ -380,7 +393,8 @@ class BrokenProcessPool(RuntimeError):
class ProcessPoolExecutor(_base.Executor):
def __init__(self, max_workers=None, mp_context=None):
def __init__(self, max_workers=None, mp_context=None,
initializer=None, initargs=()):
"""Initializes a new ProcessPoolExecutor instance.
Args:
@ -389,6 +403,8 @@ class ProcessPoolExecutor(_base.Executor):
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.
initializer: An callable used to initialize worker processes.
initargs: A tuple of arguments to pass to the initializer.
"""
_check_system_limits()
@ -403,6 +419,11 @@ class ProcessPoolExecutor(_base.Executor):
mp_context = mp.get_context()
self._mp_context = mp_context
if initializer is not None and not callable(initializer):
raise TypeError("initializer must be a callable")
self._initializer = initializer
self._initargs = initargs
# 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.
@ -450,15 +471,16 @@ class ProcessPoolExecutor(_base.Executor):
p = self._mp_context.Process(
target=_process_worker,
args=(self._call_queue,
self._result_queue))
self._result_queue,
self._initializer,
self._initargs))
p.start()
self._processes[p.pid] = p
def submit(self, fn, *args, **kwargs):
with self._shutdown_lock:
if self._broken:
raise BrokenProcessPool('A child process terminated '
'abruptly, the process pool is not usable anymore')
raise BrokenProcessPool(self._broken)
if self._shutdown_thread:
raise RuntimeError('cannot schedule new futures after shutdown')

51
Lib/concurrent/futures/thread.py
View File

@ -41,6 +41,7 @@ def _python_exit():
atexit.register(_python_exit)
class _WorkItem(object):
def __init__(self, future, fn, args, kwargs):
self.future = future
@ -61,7 +62,17 @@ class _WorkItem(object):
else:
self.future.set_result(result)
def _worker(executor_reference, work_queue):
def _worker(executor_reference, work_queue, initializer, initargs):
if initializer is not None:
try:
initializer(*initargs)
except BaseException:
_base.LOGGER.critical('Exception in initializer:', exc_info=True)
executor = executor_reference()
if executor is not None:
executor._initializer_failed()
return
try:
while True:
work_item = work_queue.get(block=True)
@ -83,18 +94,28 @@ def _worker(executor_reference, work_queue):
except BaseException:
_base.LOGGER.critical('Exception in worker', exc_info=True)
class BrokenThreadPool(_base.BrokenExecutor):
"""
Raised when a worker thread in a ThreadPoolExecutor failed initializing.
"""
class ThreadPoolExecutor(_base.Executor):
# Used to assign unique thread names when thread_name_prefix is not supplied.
_counter = itertools.count().__next__
def __init__(self, max_workers=None, thread_name_prefix=''):
def __init__(self, max_workers=None, thread_name_prefix='',
initializer=None, initargs=()):
"""Initializes a new ThreadPoolExecutor instance.
Args:
max_workers: The maximum number of threads that can be used to
execute the given calls.
thread_name_prefix: An optional name prefix to give our threads.
initializer: An callable used to initialize worker threads.
initargs: A tuple of arguments to pass to the initializer.
"""
if max_workers is None:
# Use this number because ThreadPoolExecutor is often
@ -103,16 +124,25 @@ class ThreadPoolExecutor(_base.Executor):
if max_workers <= 0:
raise ValueError("max_workers must be greater than 0")
if initializer is not None and not callable(initializer):
raise TypeError("initializer must be a callable")
self._max_workers = max_workers
self._work_queue = queue.Queue()
self._threads = set()
self._broken = False
self._shutdown = False
self._shutdown_lock = threading.Lock()
self._thread_name_prefix = (thread_name_prefix or
("ThreadPoolExecutor-%d" % self._counter()))
self._initializer = initializer
self._initargs = initargs
def submit(self, fn, *args, **kwargs):
with self._shutdown_lock:
if self._broken:
raise BrokenThreadPool(self._broken)
if self._shutdown:
raise RuntimeError('cannot schedule new futures after shutdown')
@ -137,12 +167,27 @@ class ThreadPoolExecutor(_base.Executor):
num_threads)
t = threading.Thread(name=thread_name, target=_worker,
args=(weakref.ref(self, weakref_cb),
self._work_queue))
self._work_queue,
self._initializer,
self._initargs))
t.daemon = True
t.start()
self._threads.add(t)
_threads_queues[t] = self._work_queue
def _initializer_failed(self):
with self._shutdown_lock:
self._broken = ('A thread initializer failed, the thread pool '
'is not usable anymore')
# Drain work queue and mark pending futures failed
while True:
try:
work_item = self._work_queue.get_nowait()
except queue.Empty:
break
if work_item is not None:
work_item.future.set_exception(BrokenThreadPool(self._broken))
def shutdown(self, wait=True):
with self._shutdown_lock:
self._shutdown = True

184
Lib/test/test_concurrent_futures.py
View File

@ -7,6 +7,7 @@ test.support.import_module('multiprocessing.synchronize')
from test.support.script_helper import assert_python_ok
import contextlib
import itertools
import os
import sys
@ -17,7 +18,8 @@ import weakref
from concurrent import futures
from concurrent.futures._base import (
PENDING, RUNNING, CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED, Future)
PENDING, RUNNING, CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED, Future,
BrokenExecutor)
from concurrent.futures.process import BrokenProcessPool
from multiprocessing import get_context
@ -37,11 +39,12 @@ CANCELLED_AND_NOTIFIED_FUTURE = create_future(state=CANCELLED_AND_NOTIFIED)
EXCEPTION_FUTURE = create_future(state=FINISHED, exception=OSError())
SUCCESSFUL_FUTURE = create_future(state=FINISHED, result=42)
INITIALIZER_STATUS = 'uninitialized'
def mul(x, y):
return x * y
def sleep_and_raise(t):
time.sleep(t)
raise Exception('this is an exception')
@ -51,6 +54,17 @@ def sleep_and_print(t, msg):
print(msg)
sys.stdout.flush()
def init(x):
global INITIALIZER_STATUS
INITIALIZER_STATUS = x
def get_init_status():
return INITIALIZER_STATUS
def init_fail():
time.sleep(0.1) # let some futures be scheduled
raise ValueError('error in initializer')
class MyObject(object):
def my_method(self):
@ -81,6 +95,7 @@ class BaseTestCase(unittest.TestCase):
class ExecutorMixin:
worker_count = 5
executor_kwargs = {}
def setUp(self):
super().setUp()
@ -90,10 +105,12 @@ class ExecutorMixin:
if hasattr(self, "ctx"):
self.executor = self.executor_type(
max_workers=self.worker_count,
mp_context=get_context(self.ctx))
mp_context=get_context(self.ctx),
**self.executor_kwargs)
else:
self.executor = self.executor_type(
max_workers=self.worker_count)
max_workers=self.worker_count,
**self.executor_kwargs)
except NotImplementedError as e:
self.skipTest(str(e))
self._prime_executor()
@ -114,7 +131,6 @@ class ExecutorMixin:
# tests. This should reduce the probability of timeouts in the tests.
futures = [self.executor.submit(time.sleep, 0.1)
for _ in range(self.worker_count)]
for f in futures:
f.result()
@ -148,6 +164,90 @@ class ProcessPoolForkserverMixin(ExecutorMixin):
super().setUp()
def create_executor_tests(mixin, bases=(BaseTestCase,),
executor_mixins=(ThreadPoolMixin,
ProcessPoolForkMixin,
ProcessPoolForkserverMixin,
ProcessPoolSpawnMixin)):
def strip_mixin(name):
if name.endswith(('Mixin', 'Tests')):
return name[:-5]
elif name.endswith('Test'):
return name[:-4]
else:
return name
for exe in executor_mixins:
name = ("%s%sTest"
% (strip_mixin(exe.__name__), strip_mixin(mixin.__name__)))
cls = type(name, (mixin,) + (exe,) + bases, {})
globals()[name] = cls
class InitializerMixin(ExecutorMixin):
worker_count = 2
def setUp(self):
global INITIALIZER_STATUS
INITIALIZER_STATUS = 'uninitialized'
self.executor_kwargs = dict(initializer=init,
initargs=('initialized',))
super().setUp()
def test_initializer(self):
futures = [self.executor.submit(get_init_status)
for _ in range(self.worker_count)]
for f in futures:
self.assertEqual(f.result(), 'initialized')
class FailingInitializerMixin(ExecutorMixin):
worker_count = 2
def setUp(self):
self.executor_kwargs = dict(initializer=init_fail)
super().setUp()
def test_initializer(self):
with self._assert_logged('ValueError: error in initializer'):
try:
future = self.executor.submit(get_init_status)
except BrokenExecutor:
# Perhaps the executor is already broken
pass
else:
with self.assertRaises(BrokenExecutor):
future.result()
# At some point, the executor should break
t1 = time.time()
while not self.executor._broken:
if time.time() - t1 > 5:
self.fail("executor not broken after 5 s.")
time.sleep(0.01)
# ... and from this point submit() is guaranteed to fail
with self.assertRaises(BrokenExecutor):
self.executor.submit(get_init_status)
def _prime_executor(self):
pass
@contextlib.contextmanager
def _assert_logged(self, msg):
if self.executor_type is futures.ProcessPoolExecutor:
# No easy way to catch the child processes' stderr
yield
else:
with self.assertLogs('concurrent.futures', 'CRITICAL') as cm:
yield
self.assertTrue(any(msg in line for line in cm.output),
cm.output)
create_executor_tests(InitializerMixin)
create_executor_tests(FailingInitializerMixin)
class ExecutorShutdownTest:
def test_run_after_shutdown(self):
self.executor.shutdown()
@ -278,20 +378,11 @@ class ProcessPoolShutdownTest(ExecutorShutdownTest):
call_queue.join_thread()
class ProcessPoolForkShutdownTest(ProcessPoolForkMixin, BaseTestCase,
ProcessPoolShutdownTest):
pass
class ProcessPoolForkserverShutdownTest(ProcessPoolForkserverMixin,
BaseTestCase,
ProcessPoolShutdownTest):
pass
class ProcessPoolSpawnShutdownTest(ProcessPoolSpawnMixin, BaseTestCase,
ProcessPoolShutdownTest):
pass
create_executor_tests(ProcessPoolShutdownTest,
executor_mixins=(ProcessPoolForkMixin,
ProcessPoolForkserverMixin,
ProcessPoolSpawnMixin))
class WaitTests:
@ -413,18 +504,10 @@ class ThreadPoolWaitTests(ThreadPoolMixin, WaitTests, BaseTestCase):
sys.setswitchinterval(oldswitchinterval)
class ProcessPoolForkWaitTests(ProcessPoolForkMixin, WaitTests, BaseTestCase):
pass
class ProcessPoolForkserverWaitTests(ProcessPoolForkserverMixin, WaitTests,
BaseTestCase):
pass
class ProcessPoolSpawnWaitTests(ProcessPoolSpawnMixin, BaseTestCase,
WaitTests):
pass
create_executor_tests(WaitTests,
executor_mixins=(ProcessPoolForkMixin,
ProcessPoolForkserverMixin,
ProcessPoolSpawnMixin))
class AsCompletedTests:
@ -507,24 +590,7 @@ class AsCompletedTests:
self.assertEqual(str(cm.exception), '2 (of 4) futures unfinished')
class ThreadPoolAsCompletedTests(ThreadPoolMixin, AsCompletedTests, BaseTestCase):
pass
class ProcessPoolForkAsCompletedTests(ProcessPoolForkMixin, AsCompletedTests,
BaseTestCase):
pass
class ProcessPoolForkserverAsCompletedTests(ProcessPoolForkserverMixin,
AsCompletedTests,
BaseTestCase):
pass
class ProcessPoolSpawnAsCompletedTests(ProcessPoolSpawnMixin, AsCompletedTests,
BaseTestCase):
pass
create_executor_tests(AsCompletedTests)
class ExecutorTest:
@ -688,23 +754,10 @@ class ProcessPoolExecutorTest(ExecutorTest):
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
create_executor_tests(ProcessPoolExecutorTest,
executor_mixins=(ProcessPoolForkMixin,
ProcessPoolForkserverMixin,
ProcessPoolSpawnMixin))
class FutureTests(BaseTestCase):
@ -932,6 +985,7 @@ class FutureTests(BaseTestCase):
self.assertTrue(isinstance(f1.exception(timeout=5), OSError))
t.join()
@test.support.reap_threads
def test_main():
try:

1
Misc/NEWS.d/next/Library/2017-11-02-22-26-16.bpo-21423.hw5mEh.rst Normal file
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@ -0,0 +1 @@
Add an initializer argument to {Process,Thread}PoolExecutor