test_futures.py

import os
import subprocess
import sys
import threading
import functools
import contextlib
import logging
import re
import time
import gc
import traceback
from StringIO import StringIO
from test import test_support

from concurrent import futures
from concurrent.futures._base import (
    PENDING, RUNNING, CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED, Future, BrokenExecutor)
from concurrent.futures.thread import cpu_count

try:
    import unittest2 as unittest
except ImportError:
    import unittest


def reap_threads(func):
    """Use this function when threads are being used.  This will
    ensure that the threads are cleaned up even when the test fails.
    If threading is unavailable this function does nothing.
    """
    @functools.wraps(func)
    def decorator(*args):
        key = test_support.threading_setup()
        try:
            return func(*args)
        finally:
            test_support.threading_cleanup(*key)
    return decorator


# Executing the interpreter in a subprocess
def _assert_python(expected_success, *args, **env_vars):
    cmd_line = [sys.executable]
    if not env_vars:
        cmd_line.append('-E')
    # Need to preserve the original environment, for in-place testing of
    # shared library builds.
    env = os.environ.copy()
    # But a special flag that can be set to override -- in this case, the
    # caller is responsible to pass the full environment.
    if env_vars.pop('__cleanenv', None):
        env = {}
    env.update(env_vars)
    cmd_line.extend(args)
    p = subprocess.Popen(cmd_line, stdin=subprocess.PIPE,
                         stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                         env=env)
    try:
        out, err = p.communicate()
    finally:
        subprocess._cleanup()
        p.stdout.close()
        p.stderr.close()
    rc = p.returncode
    err = strip_python_stderr(err)
    if (rc and expected_success) or (not rc and not expected_success):
        raise AssertionError(
            "Process return code is %d, "
            "stderr follows:\n%s" % (rc, err.decode('ascii', 'ignore')))
    return rc, out, err


def assert_python_ok(*args, **env_vars):
    """
    Assert that running the interpreter with `args` and optional environment
    variables `env_vars` is ok and return a (return code, stdout, stderr) tuple.
    """
    return _assert_python(True, *args, **env_vars)


def strip_python_stderr(stderr):
    """Strip the stderr of a Python process from potential debug output
    emitted by the interpreter.

    This will typically be run on the result of the communicate() method
    of a subprocess.Popen object.
    """
    stderr = re.sub(r"\[\d+ refs\]\r?\n?$".encode(), "".encode(), stderr).strip()
    return stderr


@contextlib.contextmanager
def captured_stderr():
    """Return a context manager used by captured_stdout/stdin/stderr
    that temporarily replaces the sys stream *stream_name* with a StringIO."""
    logging_stream = StringIO()
    handler = logging.StreamHandler(logging_stream)
    logging.root.addHandler(handler)

    try:
        yield logging_stream
    finally:
        logging.root.removeHandler(handler)


def create_future(state=PENDING, exception=None, result=None):
    f = Future()
    f._state = state
    f._exception = exception
    f._result = result
    return f


PENDING_FUTURE = create_future(state=PENDING)
RUNNING_FUTURE = create_future(state=RUNNING)
CANCELLED_FUTURE = create_future(state=CANCELLED)
CANCELLED_AND_NOTIFIED_FUTURE = create_future(state=CANCELLED_AND_NOTIFIED)
EXCEPTION_FUTURE = create_future(state=FINISHED, exception=IOError())
SUCCESSFUL_FUTURE = create_future(state=FINISHED, result=42)


def mul(x, y):
    return x * y


def sleep_and_raise(t):
    time.sleep(t)
    raise Exception('this is an exception')

def sleep_and_print(t, msg):
    time.sleep(t)
    print(msg)
    sys.stdout.flush()


class ExecutorMixin:
    worker_count = 5

    def setUp(self):
        self.t1 = time.time()
        try:
            self.executor = self.executor_type(max_workers=self.worker_count)
        except NotImplementedError:
            e = sys.exc_info()[1]
            self.skipTest(str(e))
        self._prime_executor()

    def tearDown(self):
        self.executor.shutdown(wait=True)
        dt = time.time() - self.t1
        if test_support.verbose:
            print("%.2fs" % dt)
        self.assertLess(dt, 60, "synchronization issue: test lasted too long")

    def _prime_executor(self):
        # Make sure that the executor is ready to do work before running the
        # tests. This should reduce the probability of timeouts in the tests.
        futures = [self.executor.submit(time.sleep, 0.1)
                   for _ in range(self.worker_count)]

        for f in futures:
            f.result()


class ThreadPoolMixin(ExecutorMixin):
    executor_type = futures.ThreadPoolExecutor


class ProcessPoolMixin(ExecutorMixin):
    executor_type = futures.ProcessPoolExecutor


class ExecutorShutdownTest(unittest.TestCase):
    def test_run_after_shutdown(self):
        self.executor.shutdown()
        self.assertRaises(RuntimeError,
                          self.executor.submit,
                          pow, 2, 5)

    def test_interpreter_shutdown(self):
        # Test the atexit hook for shutdown of worker threads and processes
        rc, out, err = assert_python_ok('-c', """if 1:
            from concurrent.futures import %s
            from time import sleep
            from test_futures import sleep_and_print
            t = %s(5)
            t.submit(sleep_and_print, 1.0, "apple")
            """ % (self.executor_type.__name__, self.executor_type.__name__))
        # Errors in atexit hooks don't change the process exit code, check
        # stderr manually.
        self.assertFalse(err)
        self.assertEqual(out.strip(), "apple".encode())

    def test_hang_issue12364(self):
        fs = [self.executor.submit(time.sleep, 0.1) for _ in range(50)]
        self.executor.shutdown()
        for f in fs:
            f.result()


class ThreadPoolShutdownTest(ThreadPoolMixin, ExecutorShutdownTest):
    def _prime_executor(self):
        pass

    def test_threads_terminate(self):
        self.executor.submit(mul, 21, 2)
        self.executor.submit(mul, 6, 7)
        self.executor.submit(mul, 3, 14)
        def acquire_lock(lock):
            lock.acquire()

        sem = threading.Semaphore(0)
        for i in range(3):
            self.executor.submit(acquire_lock, sem)
        self.assertEqual(len(self.executor._threads), 3)
        for i in range(3):
            sem.release()
        self.executor.shutdown()
        for t in self.executor._threads:
            t.join(5)

    def test_context_manager_shutdown(self):
        with futures.ThreadPoolExecutor(max_workers=5) as e:
            executor = e
            self.assertEqual(list(e.map(abs, range(-5, 5))),
                             [5, 4, 3, 2, 1, 0, 1, 2, 3, 4])

        for t in executor._threads:
            t.join(5)

    def test_del_shutdown(self):
        executor = futures.ThreadPoolExecutor(max_workers=5)
        executor.map(abs, range(-5, 5))
        threads = executor._threads
        del executor
        gc.collect()
        gc.collect()

        for t in threads:
            t.join(5)

    def test_thread_names_assigned(self):
        executor = futures.ThreadPoolExecutor(
            max_workers=5, thread_name_prefix='SpecialPool')
        executor.map(abs, range(-5, 5))
        threads = executor._threads
        del executor
        gc.collect()
        gc.collect()

        for t in threads:
            self.assertRegexpMatches(t.name, r'^SpecialPool_[0-4]$')
            t.join(5)

    def test_thread_names_default(self):
        executor = futures.ThreadPoolExecutor(max_workers=5)
        executor.map(abs, range(-5, 5))
        threads = executor._threads
        del executor
        gc.collect()
        gc.collect()

        for t in threads:
            # Ensure that our default name is reasonably sane and unique when
            # no thread_name_prefix was supplied.
            self.assertRegexpMatches(t.name, r'ThreadPoolExecutor-\d+_[0-4]$')
            t.join(5)


class ProcessPoolShutdownTest(ProcessPoolMixin, ExecutorShutdownTest):
    def _prime_executor(self):
        pass

    def test_processes_terminate(self):
        self.executor.submit(mul, 21, 2)
        self.executor.submit(mul, 6, 7)
        self.executor.submit(mul, 3, 14)
        self.assertEqual(len(self.executor._processes), 5)
        processes = self.executor._processes
        self.executor.shutdown()

        for p in processes:
            p.join(5)

    def test_context_manager_shutdown(self):
        with futures.ProcessPoolExecutor(max_workers=5) as e:
            processes = e._processes
            self.assertEqual(list(e.map(abs, range(-5, 5))),
                             [5, 4, 3, 2, 1, 0, 1, 2, 3, 4])

        for p in processes:
            p.join(5)

    def test_del_shutdown(self):
        executor = futures.ProcessPoolExecutor(max_workers=5)
        list(executor.map(abs, range(-5, 5)))
        queue_management_thread = executor._queue_management_thread
        processes = executor._processes
        del executor
        gc.collect()
        gc.collect()

        queue_management_thread.join(5)
        for p in processes:
            p.join(5)


class WaitTests(unittest.TestCase):

    def test_first_completed(self):
        future1 = self.executor.submit(mul, 21, 2)
        future2 = self.executor.submit(time.sleep, 1.5)

        done, not_done = futures.wait(
                [CANCELLED_FUTURE, future1, future2],
                 return_when=futures.FIRST_COMPLETED)

        self.assertEqual(set([future1]), done)
        self.assertEqual(set([CANCELLED_FUTURE, future2]), not_done)

    def test_first_completed_some_already_completed(self):
        future1 = self.executor.submit(time.sleep, 1.5)

        finished, pending = futures.wait(
                 [CANCELLED_AND_NOTIFIED_FUTURE, SUCCESSFUL_FUTURE, future1],
                 return_when=futures.FIRST_COMPLETED)

        self.assertEqual(
                set([CANCELLED_AND_NOTIFIED_FUTURE, SUCCESSFUL_FUTURE]),
                finished)
        self.assertEqual(set([future1]), pending)

    def test_first_exception(self):
        future1 = self.executor.submit(mul, 2, 21)
        future2 = self.executor.submit(sleep_and_raise, 1.5)
        future3 = self.executor.submit(time.sleep, 3)

        finished, pending = futures.wait(
                [future1, future2, future3],
                return_when=futures.FIRST_EXCEPTION)

        self.assertEqual(set([future1, future2]), finished)
        self.assertEqual(set([future3]), pending)

    def test_first_exception_some_already_complete(self):
        future1 = self.executor.submit(divmod, 21, 0)
        future2 = self.executor.submit(time.sleep, 1.5)

        finished, pending = futures.wait(
                [SUCCESSFUL_FUTURE,
                 CANCELLED_FUTURE,
                 CANCELLED_AND_NOTIFIED_FUTURE,
                 future1, future2],
                return_when=futures.FIRST_EXCEPTION)

        self.assertEqual(set([SUCCESSFUL_FUTURE,
                              CANCELLED_AND_NOTIFIED_FUTURE,
                              future1]), finished)
        self.assertEqual(set([CANCELLED_FUTURE, future2]), pending)

    def test_first_exception_one_already_failed(self):
        future1 = self.executor.submit(time.sleep, 2)

        finished, pending = futures.wait(
                 [EXCEPTION_FUTURE, future1],
                 return_when=futures.FIRST_EXCEPTION)

        self.assertEqual(set([EXCEPTION_FUTURE]), finished)
        self.assertEqual(set([future1]), pending)

    def test_all_completed(self):
        future1 = self.executor.submit(divmod, 2, 0)
        future2 = self.executor.submit(mul, 2, 21)

        finished, pending = futures.wait(
                [SUCCESSFUL_FUTURE,
                 CANCELLED_AND_NOTIFIED_FUTURE,
                 EXCEPTION_FUTURE,
                 future1,
                 future2],
                return_when=futures.ALL_COMPLETED)

        self.assertEqual(set([SUCCESSFUL_FUTURE,
                              CANCELLED_AND_NOTIFIED_FUTURE,
                              EXCEPTION_FUTURE,
                              future1,
                              future2]), finished)
        self.assertEqual(set(), pending)

    def test_timeout(self):
        future1 = self.executor.submit(mul, 6, 7)
        future2 = self.executor.submit(time.sleep, 3)

        finished, pending = futures.wait(
                [CANCELLED_AND_NOTIFIED_FUTURE,
                 EXCEPTION_FUTURE,
                 SUCCESSFUL_FUTURE,
                 future1, future2],
                timeout=1.5,
                return_when=futures.ALL_COMPLETED)

        self.assertEqual(set([CANCELLED_AND_NOTIFIED_FUTURE,
                              EXCEPTION_FUTURE,
                              SUCCESSFUL_FUTURE,
                              future1]), finished)
        self.assertEqual(set([future2]), pending)


class ThreadPoolWaitTests(ThreadPoolMixin, WaitTests):

    def test_pending_calls_race(self):
        # Issue #14406: multi-threaded race condition when waiting on all
        # futures.
        event = threading.Event()
        def future_func():
            event.wait()
        oldswitchinterval = sys.getcheckinterval()
        sys.setcheckinterval(1)
        try:
            fs = set(self.executor.submit(future_func) for i in range(100))
            event.set()
            futures.wait(fs, return_when=futures.ALL_COMPLETED)
        finally:
            sys.setcheckinterval(oldswitchinterval)


class ProcessPoolWaitTests(ProcessPoolMixin, WaitTests):
    pass


class AsCompletedTests(unittest.TestCase):
    # TODO(brian@sweetapp.com): Should have a test with a non-zero timeout.
    def test_no_timeout(self):
        future1 = self.executor.submit(mul, 2, 21)
        future2 = self.executor.submit(mul, 7, 6)

        completed = set(futures.as_completed(
                [CANCELLED_AND_NOTIFIED_FUTURE,
                 EXCEPTION_FUTURE,
                 SUCCESSFUL_FUTURE,
                 future1, future2]))
        self.assertEqual(set(
                [CANCELLED_AND_NOTIFIED_FUTURE,
                 EXCEPTION_FUTURE,
                 SUCCESSFUL_FUTURE,
                 future1, future2]),
                completed)

    def test_zero_timeout(self):
        future1 = self.executor.submit(time.sleep, 2)
        completed_futures = set()
        try:
            for future in futures.as_completed(
                    [CANCELLED_AND_NOTIFIED_FUTURE,
                     EXCEPTION_FUTURE,
                     SUCCESSFUL_FUTURE,
                     future1],
                    timeout=0):
                completed_futures.add(future)
        except futures.TimeoutError:
            pass

        self.assertEqual(set([CANCELLED_AND_NOTIFIED_FUTURE,
                              EXCEPTION_FUTURE,
                              SUCCESSFUL_FUTURE]),
                         completed_futures)

    def test_duplicate_futures(self):
        # Issue 20367. Duplicate futures should not raise exceptions or give
        # duplicate responses.
        future1 = self.executor.submit(time.sleep, 2)
        completed = [f for f in futures.as_completed([future1,future1])]
        self.assertEqual(len(completed), 1)


class ThreadPoolAsCompletedTests(ThreadPoolMixin, AsCompletedTests):
    pass


class ProcessPoolAsCompletedTests(ProcessPoolMixin, AsCompletedTests):
    pass


class ExecutorTest(unittest.TestCase):
    # Executor.shutdown() and context manager usage is tested by
    # ExecutorShutdownTest.
    def test_submit(self):
        future = self.executor.submit(pow, 2, 8)
        self.assertEqual(256, future.result())

    def test_submit_keyword(self):
        future = self.executor.submit(mul, 2, y=8)
        self.assertEqual(16, future.result())

    def test_map(self):
        self.assertEqual(
                list(self.executor.map(pow, range(10), range(10))),
                list(map(pow, range(10), range(10))))

    def test_map_exception(self):
        i = self.executor.map(divmod, [1, 1, 1, 1], [2, 3, 0, 5])
        self.assertEqual(next(i), (0, 1))
        self.assertEqual(next(i), (0, 1))
        self.assertRaises(ZeroDivisionError, next, i)

    def test_map_timeout(self):
        results = []
        try:
            for i in self.executor.map(time.sleep,
                                       [0, 0, 3],
                                       timeout=1.5):
                results.append(i)
        except futures.TimeoutError:
            pass
        else:
            self.fail('expected TimeoutError')

        self.assertEqual([None, None], results)

    def test_max_workers_negative(self):
        for number in (0, -1):
            with self.assertRaises(ValueError) as cm:
                self.executor_type(max_workers=number)

            assert str(cm.exception) == "max_workers must be greater than 0"


class ThreadPoolExecutorTest(ThreadPoolMixin, ExecutorTest):
    def test_map_submits_without_iteration(self):
        """Tests verifying issue 11777."""
        finished = []
        def record_finished(n):
            finished.append(n)

        self.executor.map(record_finished, range(10))
        self.executor.shutdown(wait=True)
        self.assertEqual(len(finished), 10)

    def test_default_workers(self):
        executor = self.executor_type()
        self.assertEqual(executor._max_workers,
                         (cpu_count() or 1) * 5)

    def test_thread_initializer(self):
        initialized = []
        def initializer(i):
            initialized.append(i)
        executor = self.executor_type(initializer=initializer, initargs=(1,))
        executor.submit(time.sleep, 1)
        executor.submit(time.sleep, 1)
        executor.shutdown(wait=True)
        self.assertEqual(initialized, [1, 1])

    def test_broken_thread_initializer(self):
        def broken_initializer(i):
            raise ValueError()
        executor = self.executor_type(initializer=broken_initializer)
        with self.assertRaises(BrokenExecutor):
            executor.submit(time.sleep, 1).result()
        with self.assertRaises(BrokenExecutor):
            executor.submit(time.sleep, 1)
        executor.shutdown(wait=True)

    def test_saturation(self):
        executor = self.executor_type(4)
        def acquire_lock(lock):
            lock.acquire()

        sem = threading.Semaphore(0)
        for i in range(15 * executor._max_workers):
            executor.submit(acquire_lock, sem)
        self.assertEqual(len(executor._threads), executor._max_workers)
        for i in range(15 * executor._max_workers):
            sem.release()
        executor.shutdown(wait=True)

    def test_idle_thread_reuse(self):
        executor = self.executor_type()
        executor.submit(mul, 21, 2).result()
        time.sleep(0.001)
        executor.submit(mul, 6, 7).result()
        time.sleep(0.001)
        executor.submit(mul, 3, 14).result()
        self.assertEqual(len(executor._threads), 1)
        executor.shutdown(wait=True)


class ProcessPoolExecutorTest(ProcessPoolMixin, ExecutorTest):
    pass


class FutureTests(unittest.TestCase):
    def test_done_callback_with_result(self):
        callback_result = [None]
        def fn(callback_future):
            callback_result[0] = callback_future.result()

        f = Future()
        f.add_done_callback(fn)
        f.set_result(5)
        self.assertEqual(5, callback_result[0])

    def test_done_callback_with_exception(self):
        callback_exception = [None]
        def fn(callback_future):
            callback_exception[0] = callback_future.exception()

        f = Future()
        f.add_done_callback(fn)
        f.set_exception(Exception('test'))
        self.assertEqual(('test',), callback_exception[0].args)

    def test_done_callback_with_cancel(self):
        was_cancelled = [None]
        def fn(callback_future):
            was_cancelled[0] = callback_future.cancelled()

        f = Future()
        f.add_done_callback(fn)
        self.assertTrue(f.cancel())
        self.assertTrue(was_cancelled[0])

    def test_done_callback_raises(self):
        with captured_stderr() as stderr:
            raising_was_called = [False]
            raising_old_style_was_called = [False]
            fn_was_called = [False]

            def raising_fn(callback_future):
                raising_was_called[0] = True
                raise Exception('doh!')

            def raising_old_style_fn(callback_future):
                raising_old_style_was_called[0] = True
                class OldStyle:  # Does not inherit from object
                   def __str__(self):
                       return 'doh!'
                raise OldStyle()

            def fn(callback_future):
                fn_was_called[0] = True

            f = Future()
            f.add_done_callback(raising_fn)
            f.add_done_callback(raising_old_style_fn)
            f.add_done_callback(fn)
            f.set_result(5)
            self.assertTrue(raising_was_called)
            self.assertTrue(raising_old_style_was_called)
            self.assertTrue(fn_was_called)
            self.assertIn('Exception: doh!', stderr.getvalue())
            self.assertIn('OldStyle: doh!', stderr.getvalue())

    def test_done_callback_already_successful(self):
        callback_result = [None]
        def fn(callback_future):
            callback_result[0] = callback_future.result()

        f = Future()
        f.set_result(5)
        f.add_done_callback(fn)
        self.assertEqual(5, callback_result[0])

    def test_done_callback_already_failed(self):
        callback_exception = [None]
        def fn(callback_future):
            callback_exception[0] = callback_future.exception()

        f = Future()
        f.set_exception(Exception('test'))
        f.add_done_callback(fn)
        self.assertEqual(('test',), callback_exception[0].args)

    def test_done_callback_already_cancelled(self):
        was_cancelled = [None]
        def fn(callback_future):
            was_cancelled[0] = callback_future.cancelled()

        f = Future()
        self.assertTrue(f.cancel())
        f.add_done_callback(fn)
        self.assertTrue(was_cancelled[0])

    def test_repr(self):
        self.assertRegexpMatches(repr(PENDING_FUTURE),
                                 '<Future at 0x[0-9a-f]+L? state=pending>')
        self.assertRegexpMatches(repr(RUNNING_FUTURE),
                                 '<Future at 0x[0-9a-f]+L? state=running>')
        self.assertRegexpMatches(repr(CANCELLED_FUTURE),
                                 '<Future at 0x[0-9a-f]+L? state=cancelled>')
        self.assertRegexpMatches(repr(CANCELLED_AND_NOTIFIED_FUTURE),
                                 '<Future at 0x[0-9a-f]+L? state=cancelled>')
        self.assertRegexpMatches(
                repr(EXCEPTION_FUTURE),
                '<Future at 0x[0-9a-f]+L? state=finished raised IOError>')
        self.assertRegexpMatches(
                repr(SUCCESSFUL_FUTURE),
                '<Future at 0x[0-9a-f]+L? state=finished returned int>')

    def test_cancel(self):
        f1 = create_future(state=PENDING)
        f2 = create_future(state=RUNNING)
        f3 = create_future(state=CANCELLED)
        f4 = create_future(state=CANCELLED_AND_NOTIFIED)
        f5 = create_future(state=FINISHED, exception=IOError())
        f6 = create_future(state=FINISHED, result=5)

        self.assertTrue(f1.cancel())
        self.assertEqual(f1._state, CANCELLED)

        self.assertFalse(f2.cancel())
        self.assertEqual(f2._state, RUNNING)

        self.assertTrue(f3.cancel())
        self.assertEqual(f3._state, CANCELLED)

        self.assertTrue(f4.cancel())
        self.assertEqual(f4._state, CANCELLED_AND_NOTIFIED)

        self.assertFalse(f5.cancel())
        self.assertEqual(f5._state, FINISHED)

        self.assertFalse(f6.cancel())
        self.assertEqual(f6._state, FINISHED)

    def test_cancelled(self):
        self.assertFalse(PENDING_FUTURE.cancelled())
        self.assertFalse(RUNNING_FUTURE.cancelled())
        self.assertTrue(CANCELLED_FUTURE.cancelled())
        self.assertTrue(CANCELLED_AND_NOTIFIED_FUTURE.cancelled())
        self.assertFalse(EXCEPTION_FUTURE.cancelled())
        self.assertFalse(SUCCESSFUL_FUTURE.cancelled())

    def test_done(self):
        self.assertFalse(PENDING_FUTURE.done())
        self.assertFalse(RUNNING_FUTURE.done())
        self.assertTrue(CANCELLED_FUTURE.done())
        self.assertTrue(CANCELLED_AND_NOTIFIED_FUTURE.done())
        self.assertTrue(EXCEPTION_FUTURE.done())
        self.assertTrue(SUCCESSFUL_FUTURE.done())

    def test_running(self):
        self.assertFalse(PENDING_FUTURE.running())
        self.assertTrue(RUNNING_FUTURE.running())
        self.assertFalse(CANCELLED_FUTURE.running())
        self.assertFalse(CANCELLED_AND_NOTIFIED_FUTURE.running())
        self.assertFalse(EXCEPTION_FUTURE.running())
        self.assertFalse(SUCCESSFUL_FUTURE.running())

    def test_result_with_timeout(self):
        self.assertRaises(futures.TimeoutError,
                          PENDING_FUTURE.result, timeout=0)
        self.assertRaises(futures.TimeoutError,
                          RUNNING_FUTURE.result, timeout=0)
        self.assertRaises(futures.CancelledError,
                          CANCELLED_FUTURE.result, timeout=0)
        self.assertRaises(futures.CancelledError,
                          CANCELLED_AND_NOTIFIED_FUTURE.result, timeout=0)
        self.assertRaises(IOError, EXCEPTION_FUTURE.result, timeout=0)
        self.assertEqual(SUCCESSFUL_FUTURE.result(timeout=0), 42)

    def test_result_with_success(self):
        # TODO(brian@sweetapp.com): This test is timing dependent.
        def notification():
            # Wait until the main thread is waiting for the result.
            time.sleep(1)
            f1.set_result(42)

        f1 = create_future(state=PENDING)
        t = threading.Thread(target=notification)
        t.start()

        self.assertEqual(f1.result(timeout=5), 42)

    def test_result_with_cancel(self):
        # TODO(brian@sweetapp.com): This test is timing dependent.
        def notification():
            # Wait until the main thread is waiting for the result.
            time.sleep(1)
            f1.cancel()

        f1 = create_future(state=PENDING)
        t = threading.Thread(target=notification)
        t.start()

        self.assertRaises(futures.CancelledError, f1.result, timeout=5)

    def test_exception_with_timeout(self):
        self.assertRaises(futures.TimeoutError,
                          PENDING_FUTURE.exception, timeout=0)
        self.assertRaises(futures.TimeoutError,
                          RUNNING_FUTURE.exception, timeout=0)
        self.assertRaises(futures.CancelledError,
                          CANCELLED_FUTURE.exception, timeout=0)
        self.assertRaises(futures.CancelledError,
                          CANCELLED_AND_NOTIFIED_FUTURE.exception, timeout=0)
        self.assertTrue(isinstance(EXCEPTION_FUTURE.exception(timeout=0),
                                   IOError))
        self.assertEqual(SUCCESSFUL_FUTURE.exception(timeout=0), None)

    def test_exception_with_success(self):
        def notification():
            # Wait until the main thread is waiting for the exception.
            time.sleep(1)
            with f1._condition:
                f1._state = FINISHED
                f1._exception = IOError()
                f1._condition.notify_all()

        f1 = create_future(state=PENDING)
        t = threading.Thread(target=notification)
        t.start()

        self.assertTrue(isinstance(f1.exception(timeout=5), IOError))

    def test_old_style_exception(self):
        class OldStyle:  # Does not inherit from object
            def  __str__(self):
                return 'doh!'
        callback_exc_info = [None]
        def fn(callback_future):
            callback_exc_info[0] = callback_future.exception_info()
        f = Future()
        f.add_done_callback(fn)
        try:
            raise OldStyle()
        except OldStyle:
            want_exc_info = sys.exc_info()
            f.set_exception_info(*want_exc_info[1:])
        self.assertEqual(f.exception_info(), want_exc_info[1:])
        self.assertEqual(callback_exc_info[0], want_exc_info[1:])
        try:
            f.result()
        except OldStyle:
            got_exc_info = sys.exc_info()
        else:
            self.fail('OldStyle exception not raised')
        self.assertEqual(got_exc_info[:2], want_exc_info[:2])
        got_tb = traceback.extract_tb(got_exc_info[2])
        want_tb = traceback.extract_tb(want_exc_info[2])
        self.assertEqual(got_tb[-len(want_tb):], want_tb)

@reap_threads
def test_main():
    try:
        test_support.run_unittest(ProcessPoolExecutorTest,
                                  ThreadPoolExecutorTest,
                                  ProcessPoolWaitTests,
                                  ThreadPoolWaitTests,
                                  ProcessPoolAsCompletedTests,
                                  ThreadPoolAsCompletedTests,
                                  FutureTests,
                                  ProcessPoolShutdownTest,
                                  ThreadPoolShutdownTest)
    finally:
        test_support.reap_children()

if __name__ == "__main__":
    test_main()