Edit File: pool.py
# # 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()