# Copyright 2009 Brian Quinlan. All Rights Reserved. # Licensed to PSF under a Contributor Agreement. import logging import threading import time from collections 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): if self.num_pending_calls == len(self.finished_futures): 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. Parameters ---------- 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. Parameters ---------- 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 '' % ( hex(id(self)), _STATE_TO_DESCRIPTION_MAP[self._state], self._exception.__class__.__name__) else: return '' % ( hex(id(self)), _STATE_TO_DESCRIPTION_MAP[self._state], self._result.__class__.__name__) return '' % ( 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. Parameters ---------- 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. Parameters ---------- 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. Parameters ---------- 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)`. Parameters ---------- 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. Parameters ---------- 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