# Copyright 2009 Brian Quinlan. All Rights Reserved.

# Licensed to PSF under a Contributor Agreement.

from __future__ import absolute_import

import collections

import logging

import threading

import itertools

import time

import types

__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")

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

        self.lock = threading.Lock()

        super(_AllCompletedWaiter, self).__init__()

    def _decrement_pending_calls(self):

        with self.lock:

            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 _yield_finished_futures(fs, waiter, ref_collect):

    """

    Iterate on the list *fs*, yielding finished futures one by one in

    reverse order.

    Before yielding a future, *waiter* is removed from its waiters

    and the future is removed from each set in the collection of sets

    *ref_collect*.

    The aim of this function is to avoid keeping stale references after

    the future is yielded and before the iterator resumes.

    """

    while fs:

        f = fs[-1]

        for futures_set in ref_collect:

            futures_set.remove(f)

        with f._condition:

            f._waiters.remove(waiter)

        del f

        # Careful not to keep a reference to the popped value

        yield fs.pop()

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). If any given Futures are duplicated, they will be returned

        once.

    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()

    fs = set(fs)

    total_futures = len(fs)

    with _AcquireFutures(fs):

        finished = set(

                f for f in fs

                if f._state in [CANCELLED_AND_NOTIFIED, FINISHED])

        pending = fs - finished

        waiter = _create_and_install_waiters(fs, _AS_COMPLETED)

    finished = list(finished)

    try:

        for f in _yield_finished_futures(finished, waiter,

                                         ref_collect=(fs,)):

            f = [f]

            yield f.pop()

        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), total_futures))

            waiter.event.wait(wait_timeout)

            with waiter.lock:

                finished = waiter.finished_futures

                waiter.finished_futures = []

                waiter.event.clear()

            # reverse to keep finishing order

            finished.reverse()

            for f in _yield_finished_futures(finished, waiter,

                                             ref_collect=(fs, pending)):

                f = [f]

                yield f.pop()

    finally:

        # Remove waiter from unfinished futures

        for f in fs:

            with f._condition:

                f._waiters.remove(waiter)

DoneAndNotDoneFutures = collections.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:

        with f._condition:

            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._traceback = 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)

            except BaseException:

                # Explicitly let all other new-style exceptions through so

                # that we can catch all old-style exceptions with a simple

                # "except:" clause below.

                #

                # All old-style exception objects are instances of

                # types.InstanceType, but "except types.InstanceType:" does

                # not catch old-style exceptions for some reason.  Thus, the

                # only way to catch all old-style exceptions without catching

                # any new-style exceptions is to filter out the new-style

                # exceptions, which all derive from BaseException.

                raise

            except:

                # Because of the BaseException clause above, this handler only

                # executes for old-style exception objects.

                LOGGER.exception('exception calling callback for %r', self)

    def __repr__(self):

        with self._condition:

            if self._state == FINISHED:

                if self._exception:

                    return '<%s at %#x state=%s raised %s>' % (

                        self.__class__.__name__,

                        id(self),

                        _STATE_TO_DESCRIPTION_MAP[self._state],

                        self._exception.__class__.__name__)

                else:

                    return '<%s at %#x state=%s returned %s>' % (

                        self.__class__.__name__,

                        id(self),

                        _STATE_TO_DESCRIPTION_MAP[self._state],

                        self._result.__class__.__name__)

            return '<%s at %#x state=%s>' % (

                    self.__class__.__name__,

                    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 was 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:

            if isinstance(self._exception, types.InstanceType):

                # The exception is an instance of an old-style class, which

                # means type(self._exception) returns types.ClassType instead

                # of the exception's actual class type.

                exception_type = self._exception.__class__

            else:

                exception_type = type(self._exception)

            raise exception_type, self._exception, self._traceback

        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_info(self, timeout=None):

        """Return a tuple of (exception, traceback) 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._traceback

            self._condition.wait(timeout)

            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:

                raise CancelledError()

            elif self._state == FINISHED:

                return self._exception, self._traceback

            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.

        """

        return self.exception_info(timeout)[0]

    # 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.