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Diffstat (limited to 'concurrent/futures/_base.py')
| -rw-r--r-- | concurrent/futures/_base.py | 575 |
1 files changed, 575 insertions, 0 deletions
diff --git a/concurrent/futures/_base.py b/concurrent/futures/_base.py new file mode 100644 index 0000000..1d90211 --- /dev/null +++ b/concurrent/futures/_base.py @@ -0,0 +1,575 @@ +# Copyright 2009 Brian Quinlan. All Rights Reserved. +# Licensed to PSF under a Contributor Agreement. + +from __future__ import with_statement +import functools +import logging +import threading +import time + +try: + from collections import namedtuple +except ImportError: + from concurrent.futures._compat import namedtuple + +__author__ = 'Brian Quinlan (brian@sweetapp.com)' + +FIRST_COMPLETED = 'FIRST_COMPLETED' +FIRST_EXCEPTION = 'FIRST_EXCEPTION' +ALL_COMPLETED = 'ALL_COMPLETED' +_AS_COMPLETED = '_AS_COMPLETED' + +# Possible future states (for internal use by the futures package). +PENDING = 'PENDING' +RUNNING = 'RUNNING' +# The future was cancelled by the user... +CANCELLED = 'CANCELLED' +# ...and _Waiter.add_cancelled() was called by a worker. +CANCELLED_AND_NOTIFIED = 'CANCELLED_AND_NOTIFIED' +FINISHED = 'FINISHED' + +_FUTURE_STATES = [ + PENDING, + RUNNING, + CANCELLED, + CANCELLED_AND_NOTIFIED, + FINISHED +] + +_STATE_TO_DESCRIPTION_MAP = { + PENDING: "pending", + RUNNING: "running", + CANCELLED: "cancelled", + CANCELLED_AND_NOTIFIED: "cancelled", + FINISHED: "finished" +} + +# Logger for internal use by the futures package. +LOGGER = logging.getLogger("concurrent.futures") +STDERR_HANDLER = logging.StreamHandler() +LOGGER.addHandler(STDERR_HANDLER) + +class Error(Exception): + """Base class for all future-related exceptions.""" + pass + +class CancelledError(Error): + """The Future was cancelled.""" + pass + +class TimeoutError(Error): + """The operation exceeded the given deadline.""" + pass + +class _Waiter(object): + """Provides the event that wait() and as_completed() block on.""" + def __init__(self): + self.event = threading.Event() + self.finished_futures = [] + + def add_result(self, future): + self.finished_futures.append(future) + + def add_exception(self, future): + self.finished_futures.append(future) + + def add_cancelled(self, future): + self.finished_futures.append(future) + +class _AsCompletedWaiter(_Waiter): + """Used by as_completed().""" + + def __init__(self): + super(_AsCompletedWaiter, self).__init__() + self.lock = threading.Lock() + + def add_result(self, future): + with self.lock: + super(_AsCompletedWaiter, self).add_result(future) + self.event.set() + + def add_exception(self, future): + with self.lock: + super(_AsCompletedWaiter, self).add_exception(future) + self.event.set() + + def add_cancelled(self, future): + with self.lock: + super(_AsCompletedWaiter, self).add_cancelled(future) + self.event.set() + +class _FirstCompletedWaiter(_Waiter): + """Used by wait(return_when=FIRST_COMPLETED).""" + + def add_result(self, future): + super(_FirstCompletedWaiter, self).add_result(future) + self.event.set() + + def add_exception(self, future): + super(_FirstCompletedWaiter, self).add_exception(future) + self.event.set() + + def add_cancelled(self, future): + super(_FirstCompletedWaiter, self).add_cancelled(future) + self.event.set() + +class _AllCompletedWaiter(_Waiter): + """Used by wait(return_when=FIRST_EXCEPTION and ALL_COMPLETED).""" + + def __init__(self, num_pending_calls, stop_on_exception): + self.num_pending_calls = num_pending_calls + self.stop_on_exception = stop_on_exception + super(_AllCompletedWaiter, self).__init__() + + def _decrement_pending_calls(self): + self.num_pending_calls -= 1 + if not self.num_pending_calls: + self.event.set() + + def add_result(self, future): + super(_AllCompletedWaiter, self).add_result(future) + self._decrement_pending_calls() + + def add_exception(self, future): + super(_AllCompletedWaiter, self).add_exception(future) + if self.stop_on_exception: + self.event.set() + else: + self._decrement_pending_calls() + + def add_cancelled(self, future): + super(_AllCompletedWaiter, self).add_cancelled(future) + self._decrement_pending_calls() + +class _AcquireFutures(object): + """A context manager that does an ordered acquire of Future conditions.""" + + def __init__(self, futures): + self.futures = sorted(futures, key=id) + + def __enter__(self): + for future in self.futures: + future._condition.acquire() + + def __exit__(self, *args): + for future in self.futures: + future._condition.release() + +def _create_and_install_waiters(fs, return_when): + if return_when == _AS_COMPLETED: + waiter = _AsCompletedWaiter() + elif return_when == FIRST_COMPLETED: + waiter = _FirstCompletedWaiter() + else: + pending_count = sum( + f._state not in [CANCELLED_AND_NOTIFIED, FINISHED] for f in fs) + + if return_when == FIRST_EXCEPTION: + waiter = _AllCompletedWaiter(pending_count, stop_on_exception=True) + elif return_when == ALL_COMPLETED: + waiter = _AllCompletedWaiter(pending_count, stop_on_exception=False) + else: + raise ValueError("Invalid return condition: %r" % return_when) + + for f in fs: + f._waiters.append(waiter) + + return waiter + +def as_completed(fs, timeout=None): + """An iterator over the given futures that yields each as it completes. + + Args: + fs: The sequence of Futures (possibly created by different Executors) to + iterate over. + timeout: The maximum number of seconds to wait. If None, then there + is no limit on the wait time. + + Returns: + An iterator that yields the given Futures as they complete (finished or + cancelled). + + Raises: + TimeoutError: If the entire result iterator could not be generated + before the given timeout. + """ + if timeout is not None: + end_time = timeout + time.time() + + with _AcquireFutures(fs): + finished = set( + f for f in fs + if f._state in [CANCELLED_AND_NOTIFIED, FINISHED]) + pending = set(fs) - finished + waiter = _create_and_install_waiters(fs, _AS_COMPLETED) + + try: + for future in finished: + yield future + + while pending: + if timeout is None: + wait_timeout = None + else: + wait_timeout = end_time - time.time() + if wait_timeout < 0: + raise TimeoutError( + '%d (of %d) futures unfinished' % ( + len(pending), len(fs))) + + waiter.event.wait(wait_timeout) + + with waiter.lock: + finished = waiter.finished_futures + waiter.finished_futures = [] + waiter.event.clear() + + for future in finished: + yield future + pending.remove(future) + + finally: + for f in fs: + f._waiters.remove(waiter) + +DoneAndNotDoneFutures = namedtuple( + 'DoneAndNotDoneFutures', 'done not_done') +def wait(fs, timeout=None, return_when=ALL_COMPLETED): + """Wait for the futures in the given sequence to complete. + + Args: + fs: The sequence of Futures (possibly created by different Executors) to + wait upon. + timeout: The maximum number of seconds to wait. If None, then there + is no limit on the wait time. + return_when: Indicates when this function should return. The options + are: + + FIRST_COMPLETED - Return when any future finishes or is + cancelled. + FIRST_EXCEPTION - Return when any future finishes by raising an + exception. If no future raises an exception + then it is equivalent to ALL_COMPLETED. + ALL_COMPLETED - Return when all futures finish or are cancelled. + + Returns: + A named 2-tuple of sets. The first set, named 'done', contains the + futures that completed (is finished or cancelled) before the wait + completed. The second set, named 'not_done', contains uncompleted + futures. + """ + with _AcquireFutures(fs): + done = set(f for f in fs + if f._state in [CANCELLED_AND_NOTIFIED, FINISHED]) + not_done = set(fs) - done + + if (return_when == FIRST_COMPLETED) and done: + return DoneAndNotDoneFutures(done, not_done) + elif (return_when == FIRST_EXCEPTION) and done: + if any(f for f in done + if not f.cancelled() and f.exception() is not None): + return DoneAndNotDoneFutures(done, not_done) + + if len(done) == len(fs): + return DoneAndNotDoneFutures(done, not_done) + + waiter = _create_and_install_waiters(fs, return_when) + + waiter.event.wait(timeout) + for f in fs: + f._waiters.remove(waiter) + + done.update(waiter.finished_futures) + return DoneAndNotDoneFutures(done, set(fs) - done) + +class Future(object): + """Represents the result of an asynchronous computation.""" + + def __init__(self): + """Initializes the future. Should not be called by clients.""" + self._condition = threading.Condition() + self._state = PENDING + self._result = None + self._exception = None + self._waiters = [] + self._done_callbacks = [] + + def _invoke_callbacks(self): + for callback in self._done_callbacks: + try: + callback(self) + except Exception: + LOGGER.exception('exception calling callback for %r', self) + + def __repr__(self): + with self._condition: + if self._state == FINISHED: + if self._exception: + return '<Future at %s state=%s raised %s>' % ( + hex(id(self)), + _STATE_TO_DESCRIPTION_MAP[self._state], + self._exception.__class__.__name__) + else: + return '<Future at %s state=%s returned %s>' % ( + hex(id(self)), + _STATE_TO_DESCRIPTION_MAP[self._state], + self._result.__class__.__name__) + return '<Future at %s state=%s>' % ( + hex(id(self)), + _STATE_TO_DESCRIPTION_MAP[self._state]) + + def cancel(self): + """Cancel the future if possible. + + Returns True if the future was cancelled, False otherwise. A future + cannot be cancelled if it is running or has already completed. + """ + with self._condition: + if self._state in [RUNNING, FINISHED]: + return False + + if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]: + return True + + self._state = CANCELLED + self._condition.notify_all() + + self._invoke_callbacks() + return True + + def cancelled(self): + """Return True if the future has cancelled.""" + with self._condition: + return self._state in [CANCELLED, CANCELLED_AND_NOTIFIED] + + def running(self): + """Return True if the future is currently executing.""" + with self._condition: + return self._state == RUNNING + + def done(self): + """Return True of the future was cancelled or finished executing.""" + with self._condition: + return self._state in [CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED] + + def __get_result(self): + if self._exception: + raise self._exception + else: + return self._result + + def add_done_callback(self, fn): + """Attaches a callable that will be called when the future finishes. + + Args: + fn: A callable that will be called with this future as its only + argument when the future completes or is cancelled. The callable + will always be called by a thread in the same process in which + it was added. If the future has already completed or been + cancelled then the callable will be called immediately. These + callables are called in the order that they were added. + """ + with self._condition: + if self._state not in [CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED]: + self._done_callbacks.append(fn) + return + fn(self) + + def result(self, timeout=None): + """Return the result of the call that the future represents. + + Args: + timeout: The number of seconds to wait for the result if the future + isn't done. If None, then there is no limit on the wait time. + + Returns: + The result of the call that the future represents. + + Raises: + CancelledError: If the future was cancelled. + TimeoutError: If the future didn't finish executing before the given + timeout. + Exception: If the call raised then that exception will be raised. + """ + with self._condition: + if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]: + raise CancelledError() + elif self._state == FINISHED: + return self.__get_result() + + self._condition.wait(timeout) + + if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]: + raise CancelledError() + elif self._state == FINISHED: + return self.__get_result() + else: + raise TimeoutError() + + def exception(self, timeout=None): + """Return the exception raised by the call that the future represents. + + Args: + timeout: The number of seconds to wait for the exception if the + future isn't done. If None, then there is no limit on the wait + time. + + Returns: + The exception raised by the call that the future represents or None + if the call completed without raising. + + Raises: + CancelledError: If the future was cancelled. + TimeoutError: If the future didn't finish executing before the given + timeout. + """ + + with self._condition: + if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]: + raise CancelledError() + elif self._state == FINISHED: + return self._exception + + self._condition.wait(timeout) + + if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]: + raise CancelledError() + elif self._state == FINISHED: + return self._exception + else: + raise TimeoutError() + + # The following methods should only be used by Executors and in tests. + def set_running_or_notify_cancel(self): + """Mark the future as running or process any cancel notifications. + + Should only be used by Executor implementations and unit tests. + + If the future has been cancelled (cancel() was called and returned + True) then any threads waiting on the future completing (though calls + to as_completed() or wait()) are notified and False is returned. + + If the future was not cancelled then it is put in the running state + (future calls to running() will return True) and True is returned. + + This method should be called by Executor implementations before + executing the work associated with this future. If this method returns + False then the work should not be executed. + + Returns: + False if the Future was cancelled, True otherwise. + + Raises: + RuntimeError: if this method was already called or if set_result() + or set_exception() was called. + """ + with self._condition: + if self._state == CANCELLED: + self._state = CANCELLED_AND_NOTIFIED + for waiter in self._waiters: + waiter.add_cancelled(self) + # self._condition.notify_all() is not necessary because + # self.cancel() triggers a notification. + return False + elif self._state == PENDING: + self._state = RUNNING + return True + else: + LOGGER.critical('Future %s in unexpected state: %s', + id(self.future), + self.future._state) + raise RuntimeError('Future in unexpected state') + + def set_result(self, result): + """Sets the return value of work associated with the future. + + Should only be used by Executor implementations and unit tests. + """ + with self._condition: + self._result = result + self._state = FINISHED + for waiter in self._waiters: + waiter.add_result(self) + self._condition.notify_all() + self._invoke_callbacks() + + def set_exception(self, exception): + """Sets the result of the future as being the given exception. + + Should only be used by Executor implementations and unit tests. + """ + with self._condition: + self._exception = exception + self._state = FINISHED + for waiter in self._waiters: + waiter.add_exception(self) + self._condition.notify_all() + self._invoke_callbacks() + +class Executor(object): + """This is an abstract base class for concrete asynchronous executors.""" + + def submit(self, fn, *args, **kwargs): + """Submits a callable to be executed with the given arguments. + + Schedules the callable to be executed as fn(*args, **kwargs) and returns + a Future instance representing the execution of the callable. + + Returns: + A Future representing the given call. + """ + raise NotImplementedError() + + def map(self, fn, *iterables, **kwargs): + """Returns a iterator equivalent to map(fn, iter). + + Args: + fn: A callable that will take take as many arguments as there are + passed iterables. + timeout: The maximum number of seconds to wait. If None, then there + is no limit on the wait time. + + Returns: + An iterator equivalent to: map(func, *iterables) but the calls may + be evaluated out-of-order. + + Raises: + TimeoutError: If the entire result iterator could not be generated + before the given timeout. + Exception: If fn(*args) raises for any values. + """ + timeout = kwargs.get('timeout') + if timeout is not None: + end_time = timeout + time.time() + + fs = [self.submit(fn, *args) for args in zip(*iterables)] + + try: + for future in fs: + if timeout is None: + yield future.result() + else: + yield future.result(end_time - time.time()) + finally: + for future in fs: + future.cancel() + + def shutdown(self, wait=True): + """Clean-up the resources associated with the Executor. + + It is safe to call this method several times. Otherwise, no other + methods can be called after this one. + + Args: + wait: If True then shutdown will not return until all running + futures have finished executing and the resources used by the + executor have been reclaimed. + """ + pass + + def __enter__(self): + return self + + def __exit__(self, exc_type, exc_val, exc_tb): + self.shutdown(wait=True) + return False |