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#
# Module providing the `Pool` class for managing a process pool
#
# multiprocessing/pool.py
#
# Copyright (c) 2006-2008, R Oudkerk
# Licensed to PSF under a Contributor Agreement.
#
__all__ = ['Pool', 'ThreadPool']
#
# Imports
#
import collections
import itertools
import os
import queue
import threading
import time
import traceback
import warnings
from queue import Empty
# If threading is available then ThreadPool should be provided. Therefore
# we avoid top-level imports which are liable to fail on some systems.
from . import util
from . import get_context, TimeoutError
from .connection import wait
#
# Constants representing the state of a pool
#
INIT = "INIT"
RUN = "RUN"
CLOSE = "CLOSE"
TERMINATE = "TERMINATE"
#
# Miscellaneous
#
job_counter = itertools.count()
def mapstar(args):
return list(map(*args))
def starmapstar(args):
return list(itertools.starmap(args[0], args[1]))
#
# Hack to embed stringification of remote traceback in local traceback
#
class RemoteTraceback(Exception):
def __init__(self, tb):
self.tb = tb
def __str__(self):
return self.tb
class ExceptionWithTraceback:
def __init__(self, exc, tb):
tb = traceback.format_exception(type(exc), exc, tb)
tb = ''.join(tb)
self.exc = exc
self.tb = '\n"""\n%s"""' % tb
def __reduce__(self):
return rebuild_exc, (self.exc, self.tb)
def rebuild_exc(exc, tb):
exc.__cause__ = RemoteTraceback(tb)
return exc
#
# Code run by worker processes
#
class MaybeEncodingError(Exception):
"""Wraps possible unpickleable errors, so they can be
safely sent through the socket."""
def __init__(self, exc, value):
self.exc = repr(exc)
self.value = repr(value)
super(MaybeEncodingError, self).__init__(self.exc, self.value)
def __str__(self):
return "Error sending result: '%s'. Reason: '%s'" % (self.value,
self.exc)
def __repr__(self):
return "<%s: %s>" % (self.__class__.__name__, self)
def worker(inqueue, outqueue, initializer=None, initargs=(), maxtasks=None,
wrap_exception=False):
if (maxtasks is not None) and not (isinstance(maxtasks, int)
and maxtasks >= 1):
raise AssertionError("Maxtasks {!r} is not valid".format(maxtasks))
put = outqueue.put
get = inqueue.get
if hasattr(inqueue, '_writer'):
inqueue._writer.close()
outqueue._reader.close()
if initializer is not None:
initializer(*initargs)
completed = 0
while maxtasks is None or (maxtasks and completed < maxtasks):
try:
task = get()
except (EOFError, OSError):
util.debug('worker got EOFError or OSError -- exiting')
break
if task is None:
util.debug('worker got sentinel -- exiting')
break
job, i, func, args, kwds = task
try:
result = (True, func(*args, **kwds))
except Exception as e:
if wrap_exception and func is not _helper_reraises_exception:
e = ExceptionWithTraceback(e, e.__traceback__)
result = (False, e)
try:
put((job, i, result))
except Exception as e:
wrapped = MaybeEncodingError(e, result[1])
util.debug("Possible encoding error while sending result: %s" % (
wrapped))
put((job, i, (False, wrapped)))
task = job = result = func = args = kwds = None
completed += 1
util.debug('worker exiting after %d tasks' % completed)
def _helper_reraises_exception(ex):
'Pickle-able helper function for use by _guarded_task_generation.'
raise ex
#
# Class representing a process pool
#
class _PoolCache(dict):
"""
Class that implements a cache for the Pool class that will notify
the pool management threads every time the cache is emptied. The
notification is done by the use of a queue that is provided when
instantiating the cache.
"""
def __init__(self, /, *args, notifier=None, **kwds):
self.notifier = notifier
super().__init__(*args, **kwds)
def __delitem__(self, item):
super().__delitem__(item)
# Notify that the cache is empty. This is important because the
# pool keeps maintaining workers until the cache gets drained. This
# eliminates a race condition in which a task is finished after the
# the pool's _handle_workers method has enter another iteration of the
# loop. In this situation, the only event that can wake up the pool
# is the cache to be emptied (no more tasks available).
if not self:
self.notifier.put(None)
class Pool(object):
'''
Class which supports an async version of applying functions to arguments.
'''
_wrap_exception = True
@staticmethod
def Process(ctx, *args, **kwds):
return ctx.Process(*args, **kwds)
def __init__(self, processes=None, initializer=None, initargs=(),
maxtasksperchild=None, context=None):
# Attributes initialized early to make sure that they exist in
# __del__() if __init__() raises an exception
self._pool = []
self._state = INIT
self._ctx = context or get_context()
self._setup_queues()
self._taskqueue = queue.SimpleQueue()
# The _change_notifier queue exist to wake up self._handle_workers()
# when the cache (self._cache) is empty or when there is a change in
# the _state variable of the thread that runs _handle_workers.
self._change_notifier = self._ctx.SimpleQueue()
self._cache = _PoolCache(notifier=self._change_notifier)
self._maxtasksperchild = maxtasksperchild
self._initializer = initializer
self._initargs = initargs
if processes is None:
processes = os.cpu_count() or 1
if processes < 1:
raise ValueError("Number of processes must be at least 1")
if initializer is not None and not callable(initializer):
raise TypeError('initializer must be a callable')
self._processes = processes
try:
self._repopulate_pool()
except Exception:
for p in self._pool:
if p.exitcode is None:
p.terminate()
for p in self._pool:
p.join()
raise
sentinels = self._get_sentinels()
self._worker_handler = threading.Thread(
target=Pool._handle_workers,
args=(self._cache, self._taskqueue, self._ctx, self.Process,
self._processes, self._pool, self._inqueue, self._outqueue,
self._initializer, self._initargs, self._maxtasksperchild,
self._wrap_exception, sentinels, self._change_notifier)
)
self._worker_handler.daemon = True
self._worker_handler._state = RUN
self._worker_handler.start()
self._task_handler = threading.Thread(
target=Pool._handle_tasks,
args=(self._taskqueue, self._quick_put, self._outqueue,
self._pool, self._cache)
)
self._task_handler.daemon = True
self._task_handler._state = RUN
self._task_handler.start()
self._result_handler = threading.Thread(
target=Pool._handle_results,
args=(self._outqueue, self._quick_get, self._cache)
)
self._result_handler.daemon = True
self._result_handler._state = RUN
self._result_handler.start()
self._terminate = util.Finalize(
self, self._terminate_pool,
args=(self._taskqueue, self._inqueue, self._outqueue, self._pool,
self._change_notifier, self._worker_handler, self._task_handler,
self._result_handler, self._cache),
exitpriority=15
)
self._state = RUN
# Copy globals as function locals to make sure that they are available
# during Python shutdown when the Pool is destroyed.
def __del__(self, _warn=warnings.warn, RUN=RUN):
if self._state == RUN:
_warn(f"unclosed running multiprocessing pool {self!r}",
ResourceWarning, source=self)
if getattr(self, '_change_notifier', None) is not None:
self._change_notifier.put(None)
def __repr__(self):
cls = self.__class__
return (f'<{cls.__module__}.{cls.__qualname__} '
f'state={self._state} '
f'pool_size={len(self._pool)}>')
def _get_sentinels(self):
task_queue_sentinels = [self._outqueue._reader]
self_notifier_sentinels = [self._change_notifier._reader]
return [*task_queue_sentinels, *self_notifier_sentinels]
@staticmethod
def _get_worker_sentinels(workers):
return [worker.sentinel for worker in
workers if hasattr(worker, "sentinel")]
@staticmethod
def _join_exited_workers(pool):
"""Cleanup after any worker processes which have exited due to reaching
their specified lifetime. Returns True if any workers were cleaned up.
"""
cleaned = False
for i in reversed(range(len(pool))):
worker = pool[i]
if worker.exitcode is not None:
# worker exited
util.debug('cleaning up worker %d' % i)
worker.join()
cleaned = True
del pool[i]
return cleaned
def _repopulate_pool(self):
return self._repopulate_pool_static(self._ctx, self.Process,
self._processes,
self._pool, self._inqueue,
self._outqueue, self._initializer,
self._initargs,
self._maxtasksperchild,
self._wrap_exception)
@staticmethod
def _repopulate_pool_static(ctx, Process, processes, pool, inqueue,
outqueue, initializer, initargs,
maxtasksperchild, wrap_exception):
"""Bring the number of pool processes up to the specified number,
for use after reaping workers which have exited.
"""
for i in range(processes - len(pool)):
w = Process(ctx, target=worker,
args=(inqueue, outqueue,
initializer,
initargs, maxtasksperchild,
wrap_exception))
w.name = w.name.replace('Process', 'PoolWorker')
w.daemon = True
w.start()
pool.append(w)
util.debug('added worker')
@staticmethod
def _maintain_pool(ctx, Process, processes, pool, inqueue, outqueue,
initializer, initargs, maxtasksperchild,
wrap_exception):
"""Clean up any exited workers and start replacements for them.
"""
if Pool._join_exited_workers(pool):
Pool._repopulate_pool_static(ctx, Process, processes, pool,
inqueue, outqueue, initializer,
initargs, maxtasksperchild,
wrap_exception)
def _setup_queues(self):
self._inqueue = self._ctx.SimpleQueue()
self._outqueue = self._ctx.SimpleQueue()
self._quick_put = self._inqueue._writer.send
self._quick_get = self._outqueue._reader.recv
def _check_running(self):
if self._state != RUN:
raise ValueError("Pool not running")
def apply(self, func, args=(), kwds={}):
'''
Equivalent of `func(*args, **kwds)`.
Pool must be running.
'''
return self.apply_async(func, args, kwds).get()
def map(self, func, iterable, chunksize=None):
'''
Apply `func` to each element in `iterable`, collecting the results
in a list that is returned.
'''
return self._map_async(func, iterable, mapstar, chunksize).get()
def starmap(self, func, iterable, chunksize=None):
'''
Like `map()` method but the elements of the `iterable` are expected to
be iterables as well and will be unpacked as arguments. Hence
`func` and (a, b) becomes func(a, b).
'''
return self._map_async(func, iterable, starmapstar, chunksize).get()
def starmap_async(self, func, iterable, chunksize=None, callback=None,
error_callback=None):
'''
Asynchronous version of `starmap()` method.
'''
return self._map_async(func, iterable, starmapstar, chunksize,
callback, error_callback)
def _guarded_task_generation(self, result_job, func, iterable):
'''Provides a generator of tasks for imap and imap_unordered with
appropriate handling for iterables which throw exceptions during
iteration.'''
try:
i = -1
for i, x in enumerate(iterable):
yield (result_job, i, func, (x,), {})
except Exception as e:
yield (result_job, i+1, _helper_reraises_exception, (e,), {})
def imap(self, func, iterable, chunksize=1):
'''
Equivalent of `map()` -- can be MUCH slower than `Pool.map()`.
'''
self._check_running()
if chunksize == 1:
result = IMapIterator(self)
self._taskqueue.put(
(
self._guarded_task_generation(result._job, func, iterable),
result._set_length
))
return result
else:
if chunksize < 1:
raise ValueError(
"Chunksize must be 1+, not {0:n}".format(
chunksize))
task_batches = Pool._get_tasks(func, iterable, chunksize)
result = IMapIterator(self)
self._taskqueue.put(
(
self._guarded_task_generation(result._job,
mapstar,
task_batches),
result._set_length
))
return (item for chunk in result for item in chunk)
def imap_unordered(self, func, iterable, chunksize=1):
'''
Like `imap()` method but ordering of results is arbitrary.
'''
self._check_running()
if chunksize == 1:
result = IMapUnorderedIterator(self)
self._taskqueue.put(
(
self._guarded_task_generation(result._job, func, iterable),
result._set_length
))
return result
else:
if chunksize < 1:
raise ValueError(
"Chunksize must be 1+, not {0!r}".format(chunksize))
task_batches = Pool._get_tasks(func, iterable, chunksize)
result = IMapUnorderedIterator(self)
self._taskqueue.put(
(
self._guarded_task_generation(result._job,
mapstar,
task_batches),
result._set_length
))
return (item for chunk in result for item in chunk)
def apply_async(self, func, args=(), kwds={}, callback=None,
error_callback=None):
'''
Asynchronous version of `apply()` method.
'''
self._check_running()
result = ApplyResult(self, callback, error_callback)
self._taskqueue.put(([(result._job, 0, func, args, kwds)], None))
return result
def map_async(self, func, iterable, chunksize=None, callback=None,
error_callback=None):
'''
Asynchronous version of `map()` method.
'''
return self._map_async(func, iterable, mapstar, chunksize, callback,
error_callback)
def _map_async(self, func, iterable, mapper, chunksize=None, callback=None,
error_callback=None):
'''
Helper function to implement map, starmap and their async counterparts.
'''
self._check_running()
if not hasattr(iterable, '__len__'):
iterable = list(iterable)
if chunksize is None:
chunksize, extra = divmod(len(iterable), len(self._pool) * 4)
if extra:
chunksize += 1
if len(iterable) == 0:
chunksize = 0
task_batches = Pool._get_tasks(func, iterable, chunksize)
result = MapResult(self, chunksize, len(iterable), callback,
error_callback=error_callback)
self._taskqueue.put(
(
self._guarded_task_generation(result._job,
mapper,
task_batches),
None
)
)
return result
@staticmethod
def _wait_for_updates(sentinels, change_notifier, timeout=None):
wait(sentinels, timeout=timeout)
while not change_notifier.empty():
change_notifier.get()
@classmethod
def _handle_workers(cls, cache, taskqueue, ctx, Process, processes,
pool, inqueue, outqueue, initializer, initargs,
maxtasksperchild, wrap_exception, sentinels,
change_notifier):
thread = threading.current_thread()
# Keep maintaining workers until the cache gets drained, unless the pool
# is terminated.
while thread._state == RUN or (cache and thread._state != TERMINATE):
cls._maintain_pool(ctx, Process, processes, pool, inqueue,
outqueue, initializer, initargs,
maxtasksperchild, wrap_exception)
current_sentinels = [*cls._get_worker_sentinels(pool), *sentinels]
cls._wait_for_updates(current_sentinels, change_notifier)
# send sentinel to stop workers
taskqueue.put(None)
util.debug('worker handler exiting')
@staticmethod
def _handle_tasks(taskqueue, put, outqueue, pool, cache):
thread = threading.current_thread()
for taskseq, set_length in iter(taskqueue.get, None):
task = None
try:
# iterating taskseq cannot fail
for task in taskseq:
if thread._state != RUN:
util.debug('task handler found thread._state != RUN')
break
try:
put(task)
except Exception as e:
job, idx = task[:2]
try:
cache[job]._set(idx, (False, e))
except KeyError:
pass
else:
if set_length:
util.debug('doing set_length()')
idx = task[1] if task else -1
set_length(idx + 1)
continue
break
finally:
task = taskseq = job = None
else:
util.debug('task handler got sentinel')
try:
# tell result handler to finish when cache is empty
util.debug('task handler sending sentinel to result handler')
outqueue.put(None)
# tell workers there is no more work
util.debug('task handler sending sentinel to workers')
for p in pool:
put(None)
except OSError:
util.debug('task handler got OSError when sending sentinels')
util.debug('task handler exiting')
@staticmethod
def _handle_results(outqueue, get, cache):
thread = threading.current_thread()
while 1:
try:
task = get()
except (OSError, EOFError):
util.debug('result handler got EOFError/OSError -- exiting')
return
if thread._state != RUN:
assert thread._state == TERMINATE, "Thread not in TERMINATE"
util.debug('result handler found thread._state=TERMINATE')
break
if task is None:
util.debug('result handler got sentinel')
break
job, i, obj = task
try:
cache[job]._set(i, obj)
except KeyError:
pass
task = job = obj = None
while cache and thread._state != TERMINATE:
try:
task = get()
except (OSError, EOFError):
util.debug('result handler got EOFError/OSError -- exiting')
return
if task is None:
util.debug('result handler ignoring extra sentinel')
continue
job, i, obj = task
try:
cache[job]._set(i, obj)
except KeyError:
pass
task = job = obj = None
if hasattr(outqueue, '_reader'):
util.debug('ensuring that outqueue is not full')
# If we don't make room available in outqueue then
# attempts to add the sentinel (None) to outqueue may
# block. There is guaranteed to be no more than 2 sentinels.
try:
for i in range(10):
if not outqueue._reader.poll():
break
get()
except (OSError, EOFError):
pass
util.debug('result handler exiting: len(cache)=%s, thread._state=%s',
len(cache), thread._state)
@staticmethod
def _get_tasks(func, it, size):
it = iter(it)
while 1:
x = tuple(itertools.islice(it, size))
if not x:
return
yield (func, x)
def __reduce__(self):
raise NotImplementedError(
'pool objects cannot be passed between processes or pickled'
)
def close(self):
util.debug('closing pool')
if self._state == RUN:
self._state = CLOSE
self._worker_handler._state = CLOSE
self._change_notifier.put(None)
def terminate(self):
util.debug('terminating pool')
self._state = TERMINATE
self._terminate()
def join(self):
util.debug('joining pool')
if self._state == RUN:
raise ValueError("Pool is still running")
elif self._state not in (CLOSE, TERMINATE):
raise ValueError("In unknown state")
self._worker_handler.join()
self._task_handler.join()
self._result_handler.join()
for p in self._pool:
p.join()
@staticmethod
def _help_stuff_finish(inqueue, task_handler, size):
# task_handler may be blocked trying to put items on inqueue
util.debug('removing tasks from inqueue until task handler finished')
inqueue._rlock.acquire()
while task_handler.is_alive() and inqueue._reader.poll():
inqueue._reader.recv()
time.sleep(0)
@classmethod
def _terminate_pool(cls, taskqueue, inqueue, outqueue, pool, change_notifier,
worker_handler, task_handler, result_handler, cache):
# this is guaranteed to only be called once
util.debug('finalizing pool')
# Notify that the worker_handler state has been changed so the
# _handle_workers loop can be unblocked (and exited) in order to
# send the finalization sentinel all the workers.
worker_handler._state = TERMINATE
change_notifier.put(None)
task_handler._state = TERMINATE
util.debug('helping task handler/workers to finish')
cls._help_stuff_finish(inqueue, task_handler, len(pool))
if (not result_handler.is_alive()) and (len(cache) != 0):
raise AssertionError(
"Cannot have cache with result_hander not alive")
result_handler._state = TERMINATE
change_notifier.put(None)
outqueue.put(None) # sentinel
# We must wait for the worker handler to exit before terminating
# workers because we don't want workers to be restarted behind our back.
util.debug('joining worker handler')
if threading.current_thread() is not worker_handler:
worker_handler.join()
# Terminate workers which haven't already finished.
if pool and hasattr(pool[0], 'terminate'):
util.debug('terminating workers')
for p in pool:
if p.exitcode is None:
p.terminate()
util.debug('joining task handler')
if threading.current_thread() is not task_handler:
task_handler.join()
util.debug('joining result handler')
if threading.current_thread() is not result_handler:
result_handler.join()
if pool and hasattr(pool[0], 'terminate'):
util.debug('joining pool workers')
for p in pool:
if p.is_alive():
# worker has not yet exited
util.debug('cleaning up worker %d' % p.pid)
p.join()
def __enter__(self):
self._check_running()
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.terminate()
#
# Class whose instances are returned by `Pool.apply_async()`
#
class ApplyResult(object):
def __init__(self, pool, callback, error_callback):
self._pool = pool
self._event = threading.Event()
self._job = next(job_counter)
self._cache = pool._cache
self._callback = callback
self._error_callback = error_callback
self._cache[self._job] = self
def ready(self):
return self._event.is_set()
def successful(self):
if not self.ready():
raise ValueError("{0!r} not ready".format(self))
return self._success
def wait(self, timeout=None):
self._event.wait(timeout)
def get(self, timeout=None):
self.wait(timeout)
if not self.ready():
raise TimeoutError
if self._success:
return self._value
else:
raise self._value
def _set(self, i, obj):
self._success, self._value = obj
if self._callback and self._success:
self._callback(self._value)
if self._error_callback and not self._success:
self._error_callback(self._value)
self._event.set()
del self._cache[self._job]
self._pool = None
AsyncResult = ApplyResult # create alias -- see #17805
#
# Class whose instances are returned by `Pool.map_async()`
#
class MapResult(ApplyResult):
def __init__(self, pool, chunksize, length, callback, error_callback):
ApplyResult.__init__(self, pool, callback,
error_callback=error_callback)
self._success = True
self._value = [None] * length
self._chunksize = chunksize
if chunksize <= 0:
self._number_left = 0
self._event.set()
del self._cache[self._job]
else:
self._number_left = length//chunksize + bool(length % chunksize)
def _set(self, i, success_result):
self._number_left -= 1
success, result = success_result
if success and self._success:
self._value[i*self._chunksize:(i+1)*self._chunksize] = result
if self._number_left == 0:
if self._callback:
self._callback(self._value)
del self._cache[self._job]
self._event.set()
self._pool = None
else:
if not success and self._success:
# only store first exception
self._success = False
self._value = result
if self._number_left == 0:
# only consider the result ready once all jobs are done
if self._error_callback:
self._error_callback(self._value)
del self._cache[self._job]
self._event.set()
self._pool = None
#
# Class whose instances are returned by `Pool.imap()`
#
class IMapIterator(object):
def __init__(self, pool):
self._pool = pool
self._cond = threading.Condition(threading.Lock())
self._job = next(job_counter)
self._cache = pool._cache
self._items = collections.deque()
self._index = 0
self._length = None
self._unsorted = {}
self._cache[self._job] = self
def __iter__(self):
return self
def next(self, timeout=None):
with self._cond:
try:
item = self._items.popleft()
except IndexError:
if self._index == self._length:
self._pool = None
raise StopIteration from None
self._cond.wait(timeout)
try:
item = self._items.popleft()
except IndexError:
if self._index == self._length:
self._pool = None
raise StopIteration from None
raise TimeoutError from None
success, value = item
if success:
return value
raise value
__next__ = next # XXX
def _set(self, i, obj):
with self._cond:
if self._index == i:
self._items.append(obj)
self._index += 1
while self._index in self._unsorted:
obj = self._unsorted.pop(self._index)
self._items.append(obj)
self._index += 1
self._cond.notify()
else:
self._unsorted[i] = obj
if self._index == self._length:
del self._cache[self._job]
self._pool = None
def _set_length(self, length):
with self._cond:
self._length = length
if self._index == self._length:
self._cond.notify()
del self._cache[self._job]
self._pool = None
#
# Class whose instances are returned by `Pool.imap_unordered()`
#
class IMapUnorderedIterator(IMapIterator):
def _set(self, i, obj):
with self._cond:
self._items.append(obj)
self._index += 1
self._cond.notify()
if self._index == self._length:
del self._cache[self._job]
self._pool = None
#
#
#
class ThreadPool(Pool):
_wrap_exception = False
@staticmethod
def Process(ctx, *args, **kwds):
from .dummy import Process
return Process(*args, **kwds)
def __init__(self, processes=None, initializer=None, initargs=()):
Pool.__init__(self, processes, initializer, initargs)
def _setup_queues(self):
self._inqueue = queue.SimpleQueue()
self._outqueue = queue.SimpleQueue()
self._quick_put = self._inqueue.put
self._quick_get = self._outqueue.get
def _get_sentinels(self):
return [self._change_notifier._reader]
@staticmethod
def _get_worker_sentinels(workers):
return []
@staticmethod
def _help_stuff_finish(inqueue, task_handler, size):
# drain inqueue, and put sentinels at its head to make workers finish
try:
while True:
inqueue.get(block=False)
except queue.Empty:
pass
for i in range(size):
inqueue.put(None)
def _wait_for_updates(self, sentinels, change_notifier, timeout):
time.sleep(timeout)