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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 threading
import queue
import itertools
import collections
import os
import time
import traceback
# 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
#
# Constants representing the state of a pool
#
RUN = 0
CLOSE = 1
TERMINATE = 2
#
# 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):
assert maxtasks is None or (type(maxtasks) == int and maxtasks > 0)
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 Pool(object):
'''
Class which supports an async version of applying functions to arguments.
'''
_wrap_exception = True
def Process(self, *args, **kwds):
return self._ctx.Process(*args, **kwds)
def __init__(self, processes=None, initializer=None, initargs=(),
maxtasksperchild=None, context=None):
self._ctx = context or get_context()
self._setup_queues()
self._taskqueue = queue.Queue()
self._cache = {}
self._state = RUN
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
self._pool = []
self._repopulate_pool()
self._worker_handler = threading.Thread(
target=Pool._handle_workers,
args=(self, )
)
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._worker_handler, self._task_handler,
self._result_handler, self._cache),
exitpriority=15
)
def _join_exited_workers(self):
"""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(self._pool))):
worker = self._pool[i]
if worker.exitcode is not None:
# worker exited
util.debug('cleaning up worker %d' % i)
worker.join()
cleaned = True
del self._pool[i]
return cleaned
def _repopulate_pool(self):
"""Bring the number of pool processes up to the specified number,
for use after reaping workers which have exited.
"""
for i in range(self._processes - len(self._pool)):
w = self.Process(target=worker,
args=(self._inqueue, self._outqueue,
self._initializer,
self._initargs, self._maxtasksperchild,
self._wrap_exception)
)
self._pool.append(w)
w.name = w.name.replace('Process', 'PoolWorker')
w.daemon = True
w.start()
util.debug('added worker')
def _maintain_pool(self):
"""Clean up any exited workers and start replacements for them.
"""
if self._join_exited_workers():
self._repopulate_pool()
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 apply(self, func, args=(), kwds={}):
'''
Equivalent of `func(*args, **kwds)`.
'''
assert self._state == RUN
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()`.
'''
if self._state != RUN:
raise ValueError("Pool not running")
if chunksize == 1:
result = IMapIterator(self._cache)
self._taskqueue.put(
(
self._guarded_task_generation(result._job, func, iterable),
result._set_length
))
return result
else:
assert chunksize > 1
task_batches = Pool._get_tasks(func, iterable, chunksize)
result = IMapIterator(self._cache)
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.
'''
if self._state != RUN:
raise ValueError("Pool not running")
if chunksize == 1:
result = IMapUnorderedIterator(self._cache)
self._taskqueue.put(
(
self._guarded_task_generation(result._job, func, iterable),
result._set_length
))
return result
else:
assert chunksize > 1
task_batches = Pool._get_tasks(func, iterable, chunksize)
result = IMapUnorderedIterator(self._cache)
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.
'''
if self._state != RUN:
raise ValueError("Pool not running")
result = ApplyResult(self._cache, 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.
'''
if self._state != RUN:
raise ValueError("Pool not 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._cache, 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 _handle_workers(pool):
thread = threading.current_thread()
# Keep maintaining workers until the cache gets drained, unless the pool
# is terminated.
while thread._state == RUN or (pool._cache and thread._state != TERMINATE):
pool._maintain_pool()
time.sleep(0.1)
# send sentinel to stop workers
pool._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:
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:
assert thread._state == 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
def terminate(self):
util.debug('terminating pool')
self._state = TERMINATE
self._worker_handler._state = TERMINATE
self._terminate()
def join(self):
util.debug('joining pool')
assert self._state in (CLOSE, TERMINATE)
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,
worker_handler, task_handler, result_handler, cache):
# this is guaranteed to only be called once
util.debug('finalizing pool')
worker_handler._state = TERMINATE
task_handler._state = TERMINATE
util.debug('helping task handler/workers to finish')
cls._help_stuff_finish(inqueue, task_handler, len(pool))
assert result_handler.is_alive() or len(cache) == 0
result_handler._state = TERMINATE
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):
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, cache, callback, error_callback):
self._event = threading.Event()
self._job = next(job_counter)
self._cache = cache
self._callback = callback
self._error_callback = error_callback
cache[self._job] = self
def ready(self):
return self._event.is_set()
def successful(self):
assert self.ready()
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]
AsyncResult = ApplyResult # create alias -- see #17805
#
# Class whose instances are returned by `Pool.map_async()`
#
class MapResult(ApplyResult):
def __init__(self, cache, chunksize, length, callback, error_callback):
ApplyResult.__init__(self, cache, 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 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()
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()
#
# Class whose instances are returned by `Pool.imap()`
#
class IMapIterator(object):
def __init__(self, cache):
self._cond = threading.Condition(threading.Lock())
self._job = next(job_counter)
self._cache = cache
self._items = collections.deque()
self._index = 0
self._length = None
self._unsorted = {}
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:
raise StopIteration
self._cond.wait(timeout)
try:
item = self._items.popleft()
except IndexError:
if self._index == self._length:
raise StopIteration
raise TimeoutError
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]
def _set_length(self, length):
with self._cond:
self._length = length
if self._index == self._length:
self._cond.notify()
del self._cache[self._job]
#
# 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]
#
#
#
class ThreadPool(Pool):
_wrap_exception = False
@staticmethod
def Process(*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.Queue()
self._outqueue = queue.Queue()
self._quick_put = self._inqueue.put
self._quick_get = self._outqueue.get
@staticmethod
def _help_stuff_finish(inqueue, task_handler, size):
# put sentinels at head of inqueue to make workers finish
with inqueue.not_empty:
inqueue.queue.clear()
inqueue.queue.extend([None] * size)
inqueue.not_empty.notify_all()