python - Python で TTL デコレーターを作成する

Question

Python で TTL デコレータを作成しようとしています。基本的に、関数が選択した時間内に応答しない場合、例外を発生させます。

thead2 スニペットはhttp://sebulba.wikispaces.com/recipe+thread2にあります。

from thread2 import Thread

"""  A TTL decorator. """
class Worker(Thread):
    def __init__(self, q, f, args, kvargs):
        Thread.__init__(self)

        self.q = q
        self.f = f
        self.args = args
        self.kvargs = kvargs

    def run(self,):
        try:
            res = (True, self.f(*self.args, **self.kvargs))
            self.q.put(res)
        except Exception, e:
            self.q.put((False, e))

class Referee(Thread):
    def __init__(self,q, ttl,exception_factory):
        Thread.__init__(self)

        self.exception_factory=exception_factory    
        self.q=q
        self.ttl=ttl

    def run(self):
        time.sleep(self.ttl)
        res = (False, self.exception_factory())
        self.q.put(res)

def raise_if_too_long(ttl, exception_factory=lambda :RuntimeError("Timeout")):
    def raise_if_too_long_aux(f):
        def ritl(*args,**kvargs):
            q = Queue.Queue(2)

            referee = Referee(q, ttl, exception_factory)
            worker = Worker(q,f,args,kvargs)

            worker.start()
            referee.start()

            (valid, res)= q.get(1)

            q.task_done()

            referee.terminate()
            worker.terminate()

            if valid:
                return res
            else:
                raise res

        return ritl

    return raise_if_too_long_aux

ただし、かなり悪い結果が得られます。関数が正常に返されても、TTL に達してエラーが発生するまでデコレータが返されないことがあるようです。

このコードに何か問題がありますか? PythonでTTLを使用して関数を記述する一般的な方法/ライブラリはありますか?

Answer 1

提供されたコードは、理解するのが少し難しいです。適切なスレッドの適切な場所で適切なタイミングで例外を発生させるにはどうすればよいでしょうか?

この大まかな流れを考えてみましょう:

ターゲット関数で呼び出されるデコレータ関数。次の関数を返します。

2. スレッドを開始し、ターゲット関数を呼び出します
3. thread.join([timeout]) を使用してスレッドに参加します
4. タイムアウトになった場合は、例外を発生させ、スレッドの結果を無視します。
5. タイムアウトにならない場合は、スレッドの結果を取得して返します。

(スレッドの出力をキャプチャする方法を工夫する必要があります...)

スレッドのタイムアウトについては、 http://docs.python.org/library/threading.htmlを参照してください...

(または単にerlangを使い始める :)

Answer 2

タイムアウトを超えた後に関数の実行を終了させたい場合は、その機能を持つコードを試してください。モジュールを使用するには、関数を の引数として呼び出すだけadd_timeoutで、戻り値を実行できます。呼び出されると、オブジェクトのreadyプロパティをポーリングでき、返されたものはすべてvalueプロパティを介してアクセスできます。コードのドキュメントには、利用可能な残りの API についての説明が記載されている必要があります。

[長さのために編集されたコード]ソースについては、 timeout.pyを参照してください。

---

補遺:

問題を見る別の方法があります。有効期限を持つように関数をデコレートする代わりに、関数とその引数を実行エンジンに送信して、実行できる時間にタイムアウトを強制することができます。上記の最初の回答は、約 8 年前にこの問題を解決したものでした。この件についてさらに調査した後、代わりに次のモジュールをお勧めできますか? それに続くモジュールは、モジュールの使用法をテストおよびデモンストレーションするために使用されasynchronousます。

非同期.py

#! /usr/bin/env python3
import abc as _abc
import collections as _collections
import enum as _enum
import math as _math
import multiprocessing as _multiprocessing
import operator as _operator
import queue as _queue
import signal as _signal
import sys as _sys
import time as _time

__all__ = (
    'Executor',
    'get_timeout',
    'set_timeout',
    'submit',
    'map_',
    'shutdown'
)


class _Base(metaclass=_abc.ABCMeta):
    __slots__ = (
        '__timeout',
    )

    @_abc.abstractmethod
    def __init__(self, timeout):
        self.timeout = _math.inf if timeout is None else timeout

    def get_timeout(self):
        return self.__timeout

    def set_timeout(self, value):
        if not isinstance(value, (float, int)):
            raise TypeError('value must be of type float or int')
        if value <= 0:
            raise ValueError('value must be greater than zero')
        self.__timeout = value

    timeout = property(get_timeout, set_timeout)


def _run_and_catch(fn, args, kwargs):
    # noinspection PyPep8,PyBroadException
    try:
        return False, fn(*args, **kwargs)
    except:
        return True, _sys.exc_info()[1]


def _run(fn, args, kwargs, queue):
    queue.put_nowait(_run_and_catch(fn, args, kwargs))


class _State(_enum.IntEnum):
    PENDING = _enum.auto()
    RUNNING = _enum.auto()
    CANCELLED = _enum.auto()
    FINISHED = _enum.auto()
    ERROR = _enum.auto()


def _run_and_catch_loop(iterable, *args, **kwargs):
    exception = None
    for fn in iterable:
        error, value = _run_and_catch(fn, args, kwargs)
        if error:
            exception = value
    if exception:
        raise exception


class _Future(_Base):
    __slots__ = (
        '__queue',
        '__process',
        '__start_time',
        '__callbacks',
        '__result'
    )

    def __init__(self, timeout, fn, args, kwargs):
        super().__init__(timeout)
        self.__queue = _multiprocessing.Queue(1)
        self.__process = _multiprocessing.Process(
            target=_run,
            args=(fn, args, kwargs, self.__queue),
            daemon=True
        )
        self.__start_time = _math.inf
        self.__callbacks = _collections.deque()
        self.__result = True, TimeoutError()

    @property
    def __state(self):
        pid, exitcode = self.__process.pid, self.__process.exitcode
        return (_State.PENDING if pid is None else
                _State.RUNNING if exitcode is None else
                _State.CANCELLED if exitcode == -_signal.SIGTERM else
                _State.FINISHED if exitcode == 0 else
                _State.ERROR)

    def __repr__(self):
        root = f'{type(self).__name__} at {id(self)} state={self.__state.name}'
        if self.__state < _State.CANCELLED:
            return f'<{root}>'
        error, value = self.__result
        suffix = f'{"raised" if error else "returned"} {type(value).__name__}'
        return f'<{root} {suffix}>'

    def __consume_callbacks(self):
        while self.__callbacks:
            yield self.__callbacks.popleft()

    def __invoke_callbacks(self):
        self.__process.join()
        _run_and_catch_loop(self.__consume_callbacks(), self)

    def cancel(self):
        self.__process.terminate()
        self.__invoke_callbacks()

    def __auto_cancel(self):
        elapsed_time = _time.perf_counter() - self.__start_time
        if elapsed_time > self.timeout:
            self.cancel()
        return elapsed_time

    def cancelled(self):
        self.__auto_cancel()
        return self.__state is _State.CANCELLED

    def running(self):
        self.__auto_cancel()
        return self.__state is _State.RUNNING

    def done(self):
        self.__auto_cancel()
        return self.__state > _State.RUNNING

    def __handle_result(self, error, value):
        self.__result = error, value
        self.__invoke_callbacks()

    def __ensure_termination(self):
        elapsed_time = self.__auto_cancel()
        if not self.__queue.empty():
            self.__handle_result(*self.__queue.get_nowait())
        elif self.__state < _State.CANCELLED:
            remaining_time = self.timeout - elapsed_time
            if remaining_time == _math.inf:
                remaining_time = None
            try:
                result = self.__queue.get(True, remaining_time)
            except _queue.Empty:
                self.cancel()
            else:
                self.__handle_result(*result)

    def result(self):
        self.__ensure_termination()
        error, value = self.__result
        if error:
            raise value
        return value

    def exception(self):
        self.__ensure_termination()
        error, value = self.__result
        if error:
            return value

    def add_done_callback(self, fn):
        if self.done():
            fn(self)
        else:
            self.__callbacks.append(fn)

    def _set_running_or_notify_cancel(self):
        if self.__state is _State.PENDING:
            self.__process.start()
            self.__start_time = _time.perf_counter()
        else:
            self.cancel()


class Executor(_Base):
    __slots__ = (
        '__futures',
    )

    def __init__(self, timeout=None):
        super().__init__(timeout)
        self.__futures = set()

    def submit(self, fn, *args, **kwargs):
        future = _Future(self.timeout, fn, args, kwargs)
        self.__futures.add(future)
        future.add_done_callback(self.__futures.remove)
        # noinspection PyProtectedMember
        future._set_running_or_notify_cancel()
        return future

    @staticmethod
    def __cancel_futures(iterable):
        _run_and_catch_loop(map(_operator.attrgetter('cancel'), iterable))

    def map(self, fn, *iterables):
        futures = tuple(self.submit(fn, *args) for args in zip(*iterables))

        def result_iterator():
            future_iterator = iter(futures)
            try:
                for future in future_iterator:
                    yield future.result()
            finally:
                self.__cancel_futures(future_iterator)

        return result_iterator()

    def shutdown(self):
        self.__cancel_futures(frozenset(self.__futures))

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.shutdown()
        return False


_executor = Executor()
get_timeout = _executor.get_timeout
set_timeout = _executor.set_timeout
submit = _executor.submit
map_ = _executor.map
shutdown = _executor.shutdown
del _executor

test_asynchronous.py

#! /usr/bin/env python3
import _thread
import atexit
import functools
import inspect
import io
import math
import operator
import os
import sys
import time
import unittest

import asynchronous


# noinspection PyUnresolvedReferences
class TestConstructor:
    def instantiate(self, *args):
        parameters = len(inspect.signature(self.CLASS).parameters)
        return self.CLASS(*args[:parameters])

    def test_valid_timeout(self):
        instance = self.instantiate(None, print, (), {})
        self.assertEqual(instance.get_timeout(), math.inf)
        instance = self.instantiate(1, print, (), {})
        self.assertEqual(instance.get_timeout(), 1)
        float_timeout = (math.e ** (1j * math.pi) + 1).imag
        self.assertIsInstance(float_timeout, float)
        instance = self.instantiate(float_timeout, print, (), {})
        self.assertEqual(instance.get_timeout(), float_timeout)

    def test_error_timeout(self):
        self.assertRaises(TypeError, self.instantiate, '60', print, (), {})
        self.assertRaises(ValueError, self.instantiate, 0, print, (), {})
        self.assertRaises(ValueError, self.instantiate, -1, print, (), {})


# noinspection PyUnresolvedReferences
class TestTimeout(TestConstructor):
    def test_valid_property(self):
        instance = self.instantiate(None, None, None, None)
        instance.timeout = 1
        self.assertIsInstance(instance.timeout, int)
        instance.timeout = 1 / 2
        self.assertIsInstance(instance.timeout, float)
        kilo_bit = int.from_bytes(os.urandom(1 << 7), 'big')
        instance.timeout = kilo_bit
        self.assertEqual(instance.timeout, kilo_bit)

    def test_error_property(self):
        instance = self.instantiate(None, None, None, None)
        for exception, value in (
                (TypeError, 'inf'),
                (TypeError, complex(123456789, 0)),
                (ValueError, 0),
                (ValueError, 0.0),
                (ValueError, -1),
                (ValueError, -math.pi)
        ):
            with self.assertRaises(exception):
                instance.timeout = value
            self.assertEqual(instance.timeout, math.inf)


class Timer:
    __timers = {}

    @classmethod
    def start_timer(cls):
        ident, now = _thread.get_ident(), time.perf_counter()
        if now is not cls.__timers.setdefault(ident, now):
            raise KeyError(ident)

    @classmethod
    def stop_timer(cls, expected_time, error=None):
        if error is None:
            error = 1 / 4  # the default is a quarter second
        used = time.perf_counter() - cls.__timers.pop(_thread.get_ident())
        diff = used - expected_time
        return -error <= diff <= +error


# noinspection PyUnresolvedReferences
class TestTimer(Timer):
    def stop_timer(self, expected_time, error=None):
        self.assertTrue(super().stop_timer(expected_time, error))


def delay_run(delay, fn, *args, sync=True, **kwargs):
    def wrapper():
        time.sleep(delay)
        return fn(*args, **kwargs)

    if sync:
        return wrapper()
    _thread.start_new_thread(wrapper, ())


# noinspection PyUnresolvedReferences
class TestModuleOrInstance(TestTimer):
    @property
    def moi(self):
        return self.MODULE_OR_INSTANCE

    def test_valid_timeout(self):
        self.moi.set_timeout(math.inf)
        self.assertEqual(self.moi.get_timeout(), math.inf)
        self.moi.set_timeout(60)
        self.assertEqual(self.moi.get_timeout(), 60)
        self.moi.set_timeout(0.05)
        self.assertEqual(self.moi.get_timeout(), 0.05)

    def test_error_timeout(self):
        self.moi.set_timeout(math.inf)
        self.assertRaises(TypeError, self.moi.set_timeout, None)
        self.assertEqual(self.moi.get_timeout(), math.inf)
        self.assertRaises(ValueError, self.moi.set_timeout, 0)
        self.assertEqual(self.moi.get_timeout(), math.inf)
        self.assertRaises(ValueError, self.moi.set_timeout, -1)
        self.assertEqual(self.moi.get_timeout(), math.inf)

    def run_submit_check(self):
        self.start_timer()
        future = self.moi.submit(delay_run, 0.5, operator.add, 1, 2)
        self.assertRegex(repr(future), r'^<_Future at \d+ state=RUNNING>$')
        self.assertEqual(future.result(), 3)
        self.stop_timer(0.5)
        self.assertRegex(
            repr(future),
            r'^<_Future at \d+ state=FINISHED returned int>$'
        )

    def test_submit_one_second_timeout(self):
        self.moi.set_timeout(1)
        self.run_submit_check()

    def test_submit_no_timeout(self):
        self.moi.set_timeout(math.inf)
        self.run_submit_check()

    def test_submit_short_timeout(self):
        self.moi.set_timeout(0.5)
        self.start_timer()
        future = self.moi.submit(delay_run, 1, operator.add, 1, 2)
        self.assertRegex(repr(future), r'^<_Future at \d+ state=RUNNING>$')
        self.assertIsInstance(future.exception(), TimeoutError)
        self.stop_timer(0.5)
        self.assertRegex(
            repr(future),
            r'^<_Future at \d+ state=CANCELLED raised TimeoutError>$'
        )

    def run_map(self, *args):
        return getattr(self.moi, self.NAME_OF_MAP)(delay_run, *args)

    def test_valid_map(self):
        self.moi.set_timeout(1.5)
        for result in self.run_map(
                [1, 1, 1, 1],
                [operator.add] * 4,
                [0, 1, 2, 3],
                [3, 2, 1, 0]
        ):
            self.assertEqual(result, 3)

    def test_error_map(self):
        self.moi.set_timeout(1.5)
        success = 0
        with self.assertRaises(TimeoutError):
            for result in self.run_map(
                    [1, 1, 2, 1],
                    [operator.add] * 4,
                    [0, 1, 2, 3],
                    [3, 2, 1, 0]
            ):
                self.assertEqual(result, 3)
                success += 1
        self.assertEqual(success, 2)

    def run_shutdown_check(self, running, future):
        self.assertRaises(TimeoutError, future.result)
        running.remove(future)

    def run_submit_loop(self, executor):
        running = set()
        done_callback = functools.partial(self.run_shutdown_check, running)
        for _ in range(10):
            future = executor.submit(delay_run, 2, operator.add, 10, 20)
            running.add(future)
            future.add_done_callback(done_callback)
        time.sleep(0.5)
        return running

    def test_valid_shutdown(self):
        self.moi.set_timeout(1.5)
        running = self.run_submit_loop(self.moi)
        self.moi.shutdown()
        self.assertFalse(running)

    def test_error_shutdown(self):
        self.moi.set_timeout(1.5)
        running = self.run_submit_loop(self.moi)
        running.pop()
        self.assertRaises(KeyError, self.moi.shutdown)
        self.assertFalse(running)


class TestExecutorAPI(TestTimeout, TestModuleOrInstance, unittest.TestCase):
    CLASS = asynchronous.Executor
    MODULE_OR_INSTANCE = CLASS()
    NAME_OF_MAP = 'map'

    def test_valid_context_manager(self):
        with self.instantiate(1.5) as executor:
            running = self.run_submit_loop(executor)
        self.assertFalse(running)

    def test_error_context_manager(self):
        error = Exception()
        with self.assertRaises(Exception) as cm:
            with self.instantiate(1.5) as executor:
                running = self.run_submit_loop(executor)
                raise error
        self.assertIs(cm.exception, error)
        self.assertFalse(running)
        with self.assertRaises(KeyError):
            with self.instantiate(1.5) as executor:
                running = self.run_submit_loop(executor)
                running.pop()
        self.assertFalse(running)


class TestModuleAPI(TestModuleOrInstance, unittest.TestCase):
    MODULE_OR_INSTANCE = asynchronous
    NAME_OF_MAP = 'map_'


def verify_error():
    sys.stderr.seek(0, io.SEEK_SET)
    for line in sys.stderr:
        if line == 'queue.Full\n':
            break
    else:
        sys.stderr.seek(0, io.SEEK_SET)
        sys.__stderr__.write(sys.stderr.read())
        sys.__stderr__.flush()


def cause_error(obj):
    sys.stderr = io.StringIO()
    atexit.register(verify_error)
    inspect.currentframe().f_back.f_back.f_locals['queue'].put_nowait(obj)


def return_(obj):
    return obj


# noinspection PyUnusedLocal
def throw(exception, *args):
    raise exception


class TestFutureAPI(TestTimer, TestTimeout, unittest.TestCase):
    CLASS = asynchronous._Future

    def test_valid_representation(self):
        future = self.instantiate(None, time.sleep, (0.1,), {})
        self.assertRegex(repr(future), r'^<_Future at \d+ state=PENDING>$')
        future._set_running_or_notify_cancel()
        self.assertRegex(repr(future), r'^<_Future at \d+ state=RUNNING>$')
        future._set_running_or_notify_cancel()
        self.assertRegex(
            repr(future),
            r'^<_Future at \d+ state=CANCELLED raised TimeoutError>$'
        )
        future = self.instantiate(None, time.sleep, (0.1,), {})
        future._set_running_or_notify_cancel()
        time.sleep(0.5)
        self.assertRegex(
            repr(future),
            r'^<_Future at \d+ state=FINISHED raised TimeoutError>$'
        )
        self.assertIs(future.exception(), None)
        self.assertRegex(
            repr(future),
            r'^<_Future at \d+ state=FINISHED returned NoneType>$'
        )

    def test_error_representation(self):
        future = self.instantiate(0.5, cause_error, (None,), {})
        future._set_running_or_notify_cancel()
        self.assertRaises(TypeError, future.result)
        self.assertIsInstance(future.exception(), TimeoutError)
        self.assertRegex(
            repr(future),
            r'^<_Future at \d+ state=ERROR raised TimeoutError>$'
        )
        future = self.instantiate(0.5, cause_error, ((False, 'okay'),), {})
        future._set_running_or_notify_cancel()
        self.assertEqual(future.result(), 'okay')
        self.assertRegex(
            repr(future),
            r'^<_Future at \d+ state=ERROR returned str>$'
        )

    def test_cancel(self):
        future = self.instantiate(None, time.sleep, (0.1,), {})
        self.assertRaises(AttributeError, future.cancel)
        future._set_running_or_notify_cancel()
        future.cancel()
        self.assertTrue(future.cancelled())
        future = self.instantiate(None, time.sleep, (0.1,), {})
        checker = set()
        future.add_done_callback(checker.add)
        future._set_running_or_notify_cancel()
        future.cancel()
        future.cancel()
        self.assertIs(checker.pop(), future)
        self.assertFalse(checker)

    def test_cancelled(self):
        future = self.instantiate(None, time.sleep, (0.1,), {})
        self.assertFalse(future.cancelled())
        future._set_running_or_notify_cancel()
        self.assertFalse(future.cancelled())
        self.assertIs(future.result(), None)
        self.assertFalse(future.cancelled())
        future = self.instantiate(None, time.sleep, (0.1,), {})
        future._set_running_or_notify_cancel()
        future.cancel()
        self.assertTrue(future.cancelled())
        future = self.instantiate(0.1, time.sleep, (1,), {})
        future._set_running_or_notify_cancel()
        time.sleep(0.5)
        self.assertTrue(future.cancelled())

    def test_running(self):
        future = self.instantiate(None, time.sleep, (0.1,), {})
        self.assertFalse(future.running())
        future._set_running_or_notify_cancel()
        self.assertTrue(future.running())
        self.assertIs(future.result(), None)
        self.assertFalse(future.running())
        future = self.instantiate(None, time.sleep, (0.1,), {})
        future._set_running_or_notify_cancel()
        future.cancel()
        self.assertFalse(future.running())
        future = self.instantiate(0.1, time.sleep, (1,), {})
        future._set_running_or_notify_cancel()
        time.sleep(0.5)
        self.assertFalse(future.running())

    def test_done(self):
        future = self.instantiate(None, time.sleep, (0.1,), {})
        self.assertFalse(future.done())
        future._set_running_or_notify_cancel()
        self.assertFalse(future.done())
        self.assertIs(future.result(), None)
        self.assertTrue(future.done())
        future = self.instantiate(None, time.sleep, (None,), {})
        future._set_running_or_notify_cancel()
        self.assertIsInstance(future.exception(), TypeError)
        self.assertTrue(future.done())

    def test_result_immediate(self):
        data = os.urandom(1 << 20)
        future = self.instantiate(None, return_, (data,), {})
        future._set_running_or_notify_cancel()
        self.assertEqual(future.result(), data)
        test_exception = Exception('test')
        future = self.instantiate(None, throw, (test_exception,), {})
        future._set_running_or_notify_cancel()
        with self.assertRaises(Exception) as cm:
            future.result()
        self.assertIsInstance(cm.exception, type(test_exception))
        self.assertEqual(cm.exception.args, test_exception.args)

    def test_result_delay(self):
        future = self.instantiate(None, delay_run, (0, operator.add, 1, 2), {})
        self.start_timer()
        future._set_running_or_notify_cancel()
        self.assertEqual(future.result(), 3)
        self.stop_timer(0.1)
        future = self.instantiate(None, delay_run, (1, operator.add, 2, 3), {})
        self.start_timer()
        future._set_running_or_notify_cancel()
        self.assertEqual(future.result(), 5)
        self.stop_timer(1)
        future = self.instantiate(0.5, delay_run, (0, operator.add, 1, 2), {})
        self.start_timer()
        future._set_running_or_notify_cancel()
        self.assertEqual(future.result(), 3)
        self.stop_timer(0.1)
        future = self.instantiate(0.5, delay_run, (1, operator.add, 2, 3), {})
        self.start_timer()
        future._set_running_or_notify_cancel()
        self.assertRaises(TimeoutError, future.result)
        self.stop_timer(0.5)

    def test_result_before_running(self):
        future = self.instantiate(0.1, delay_run, (0, operator.add, 1, 2), {})
        delay_run(0.5, future._set_running_or_notify_cancel, sync=False)
        self.start_timer()
        self.assertEqual(future.result(), 3)
        self.stop_timer(0.5)

    def test_exception_immediate(self):
        data = os.urandom(1 << 20)
        future = self.instantiate(None, return_, (data,), {})
        future._set_running_or_notify_cancel()
        self.assertIs(future.exception(), None)
        test_exception = Exception('test')
        future = self.instantiate(None, throw, (test_exception,), {})
        future._set_running_or_notify_cancel()
        self.assertIsInstance(future.exception(), type(test_exception))
        self.assertEqual(future.exception().args, test_exception.args)

    def test_exception_delay(self):
        future = self.instantiate(None, delay_run, (0, operator.add, 1, 2), {})
        self.start_timer()
        future._set_running_or_notify_cancel()
        self.assertIs(future.exception(), None)
        self.stop_timer(0.1)
        future = self.instantiate(None, delay_run, (1, operator.add, 2, 3), {})
        self.start_timer()
        future._set_running_or_notify_cancel()
        self.assertIs(future.exception(), None)
        self.stop_timer(1)
        future = self.instantiate(0.5, delay_run, (0, operator.add, 1, 2), {})
        self.start_timer()
        future._set_running_or_notify_cancel()
        self.assertIs(future.exception(), None)
        self.stop_timer(0.1)
        future = self.instantiate(0.5, delay_run, (1, operator.add, 2, 3), {})
        self.start_timer()
        future._set_running_or_notify_cancel()
        self.assertIsInstance(future.exception(), TimeoutError)
        self.assertFalse(future.exception().args)
        self.stop_timer(0.5)

    def test_exception_before_running(self):
        future = self.instantiate(0.1, delay_run, (0, operator.add, 1, 2), {})
        delay_run(0.5, future._set_running_or_notify_cancel, sync=False)
        self.start_timer()
        self.assertIs(future.exception(), None)
        self.stop_timer(0.5)

    def test_valid_add_done_callback(self):
        future = self.instantiate(None, time.sleep, (0,), {})
        requires_callback = {future}
        future.add_done_callback(requires_callback.remove)
        self.assertIn(future, requires_callback)
        future._set_running_or_notify_cancel()
        self.assertIs(future.exception(), None)
        self.assertFalse(requires_callback)
        requires_callback.add(future)
        future.add_done_callback(requires_callback.remove)
        self.assertFalse(requires_callback)

    def test_error_add_done_callback(self):
        future = self.instantiate(None, time.sleep, (0,), {})
        requires_callback = [{future} for _ in range(10)]
        callbacks = [s.remove for s in requires_callback]
        error = Exception()
        callbacks.insert(5, functools.partial(throw, error))
        for fn in callbacks:
            future.add_done_callback(fn)
        future._set_running_or_notify_cancel()
        with self.assertRaises(Exception) as cm:
            future.exception()
        self.assertIs(cm.exception, error)
        self.assertFalse(any(requires_callback))

    def test_set_running_or_notify_cancel(self):
        future = self.instantiate(None, time.sleep, (0.1,), {})
        self.assertFalse(future.running() or future.done())
        future._set_running_or_notify_cancel()
        self.assertTrue(future.running())
        future._set_running_or_notify_cancel()
        self.assertTrue(future.cancelled())


if __name__ == '__main__':
    unittest.main()