/Lib/test/test_asyncio/test_tasks.py

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"""Tests for tasks.py."""

import contextlib
import functools
import io
import os
import re
import sys
import types
import unittest
import weakref
from unittest import mock

import asyncio
from asyncio import coroutines
from asyncio import test_utils
try:
    from test import support
except ImportError:
    from asyncio import test_support as support
try:
    from test.support.script_helper import assert_python_ok
except ImportError:
    try:
        from test.script_helper import assert_python_ok
    except ImportError:
        from asyncio.test_support import assert_python_ok


PY34 = (sys.version_info >= (3, 4))
PY35 = (sys.version_info >= (3, 5))


@asyncio.coroutine
def coroutine_function():
    pass


@contextlib.contextmanager
def set_coroutine_debug(enabled):
    coroutines = asyncio.coroutines

    old_debug = coroutines._DEBUG
    try:
        coroutines._DEBUG = enabled
        yield
    finally:
        coroutines._DEBUG = old_debug



def format_coroutine(qualname, state, src, source_traceback, generator=False):
    if generator:
        state = '%s' % state
    else:
        state = '%s, defined' % state
    if source_traceback is not None:
        frame = source_traceback[-1]
        return ('coro=<%s() %s at %s> created at %s:%s'
                % (qualname, state, src, frame[0], frame[1]))
    else:
        return 'coro=<%s() %s at %s>' % (qualname, state, src)


class Dummy:

    def __repr__(self):
        return '<Dummy>'

    def __call__(self, *args):
        pass


class TaskTests(test_utils.TestCase):

    def setUp(self):
        self.loop = self.new_test_loop()

    def test_task_class(self):
        @asyncio.coroutine
        def notmuch():
            return 'ok'
        t = asyncio.Task(notmuch(), loop=self.loop)
        self.loop.run_until_complete(t)
        self.assertTrue(t.done())
        self.assertEqual(t.result(), 'ok')
        self.assertIs(t._loop, self.loop)

        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)
        t = asyncio.Task(notmuch(), loop=loop)
        self.assertIs(t._loop, loop)
        loop.run_until_complete(t)
        loop.close()

    def test_ensure_future_coroutine(self):
        @asyncio.coroutine
        def notmuch():
            return 'ok'
        t = asyncio.ensure_future(notmuch(), loop=self.loop)
        self.loop.run_until_complete(t)
        self.assertTrue(t.done())
        self.assertEqual(t.result(), 'ok')
        self.assertIs(t._loop, self.loop)

        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)
        t = asyncio.ensure_future(notmuch(), loop=loop)
        self.assertIs(t._loop, loop)
        loop.run_until_complete(t)
        loop.close()

    def test_ensure_future_future(self):
        f_orig = asyncio.Future(loop=self.loop)
        f_orig.set_result('ko')

        f = asyncio.ensure_future(f_orig)
        self.loop.run_until_complete(f)
        self.assertTrue(f.done())
        self.assertEqual(f.result(), 'ko')
        self.assertIs(f, f_orig)

        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        with self.assertRaises(ValueError):
            f = asyncio.ensure_future(f_orig, loop=loop)

        loop.close()

        f = asyncio.ensure_future(f_orig, loop=self.loop)
        self.assertIs(f, f_orig)

    def test_ensure_future_task(self):
        @asyncio.coroutine
        def notmuch():
            return 'ok'
        t_orig = asyncio.Task(notmuch(), loop=self.loop)
        t = asyncio.ensure_future(t_orig)
        self.loop.run_until_complete(t)
        self.assertTrue(t.done())
        self.assertEqual(t.result(), 'ok')
        self.assertIs(t, t_orig)

        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        with self.assertRaises(ValueError):
            t = asyncio.ensure_future(t_orig, loop=loop)

        loop.close()

        t = asyncio.ensure_future(t_orig, loop=self.loop)
        self.assertIs(t, t_orig)

    def test_ensure_future_neither(self):
        with self.assertRaises(TypeError):
            asyncio.ensure_future('ok')

    def test_async_warning(self):
        f = asyncio.Future(loop=self.loop)
        with self.assertWarnsRegex(DeprecationWarning,
                                   'function is deprecated, use ensure_'):
            self.assertIs(f, asyncio.async(f))

    def test_get_stack(self):
        T = None

        @asyncio.coroutine
        def foo():
            yield from bar()

        @asyncio.coroutine
        def bar():
            # test get_stack()
            f = T.get_stack(limit=1)
            try:
                self.assertEqual(f[0].f_code.co_name, 'foo')
            finally:
                f = None

            # test print_stack()
            file = io.StringIO()
            T.print_stack(limit=1, file=file)
            file.seek(0)
            tb = file.read()
            self.assertRegex(tb, r'foo\(\) running')

        @asyncio.coroutine
        def runner():
            nonlocal T
            T = asyncio.ensure_future(foo(), loop=self.loop)
            yield from T

        self.loop.run_until_complete(runner())

    def test_task_repr(self):
        self.loop.set_debug(False)

        @asyncio.coroutine
        def notmuch():
            yield from []
            return 'abc'

        # test coroutine function
        self.assertEqual(notmuch.__name__, 'notmuch')
        if PY35:
            self.assertEqual(notmuch.__qualname__,
                             'TaskTests.test_task_repr.<locals>.notmuch')
        self.assertEqual(notmuch.__module__, __name__)

        filename, lineno = test_utils.get_function_source(notmuch)
        src = "%s:%s" % (filename, lineno)

        # test coroutine object
        gen = notmuch()
        if coroutines._DEBUG or PY35:
            coro_qualname = 'TaskTests.test_task_repr.<locals>.notmuch'
        else:
            coro_qualname = 'notmuch'
        self.assertEqual(gen.__name__, 'notmuch')
        if PY35:
            self.assertEqual(gen.__qualname__,
                             coro_qualname)

        # test pending Task
        t = asyncio.Task(gen, loop=self.loop)
        t.add_done_callback(Dummy())

        coro = format_coroutine(coro_qualname, 'running', src,
                                t._source_traceback, generator=True)
        self.assertEqual(repr(t),
                         '<Task pending %s cb=[<Dummy>()]>' % coro)

        # test cancelling Task
        t.cancel()  # Does not take immediate effect!
        self.assertEqual(repr(t),
                         '<Task cancelling %s cb=[<Dummy>()]>' % coro)

        # test cancelled Task
        self.assertRaises(asyncio.CancelledError,
                          self.loop.run_until_complete, t)
        coro = format_coroutine(coro_qualname, 'done', src,
                                t._source_traceback)
        self.assertEqual(repr(t),
                         '<Task cancelled %s>' % coro)

        # test finished Task
        t = asyncio.Task(notmuch(), loop=self.loop)
        self.loop.run_until_complete(t)
        coro = format_coroutine(coro_qualname, 'done', src,
                                t._source_traceback)
        self.assertEqual(repr(t),
                         "<Task finished %s result='abc'>" % coro)

    def test_task_repr_coro_decorator(self):
        self.loop.set_debug(False)

        @asyncio.coroutine
        def notmuch():
            # notmuch() function doesn't use yield from: it will be wrapped by
            # @coroutine decorator
            return 123

        # test coroutine function
        self.assertEqual(notmuch.__name__, 'notmuch')
        if PY35:
            self.assertEqual(notmuch.__qualname__,
                             'TaskTests.test_task_repr_coro_decorator'
                             '.<locals>.notmuch')
        self.assertEqual(notmuch.__module__, __name__)

        # test coroutine object
        gen = notmuch()
        if coroutines._DEBUG or PY35:
            # On Python >= 3.5, generators now inherit the name of the
            # function, as expected, and have a qualified name (__qualname__
            # attribute).
            coro_name = 'notmuch'
            coro_qualname = ('TaskTests.test_task_repr_coro_decorator'
                             '.<locals>.notmuch')
        else:
            # On Python < 3.5, generators inherit the name of the code, not of
            # the function. See: http://bugs.python.org/issue21205
            coro_name = coro_qualname = 'coro'
        self.assertEqual(gen.__name__, coro_name)
        if PY35:
            self.assertEqual(gen.__qualname__, coro_qualname)

        # test repr(CoroWrapper)
        if coroutines._DEBUG:
            # format the coroutine object
            if coroutines._DEBUG:
                filename, lineno = test_utils.get_function_source(notmuch)
                frame = gen._source_traceback[-1]
                coro = ('%s() running, defined at %s:%s, created at %s:%s'
                        % (coro_qualname, filename, lineno,
                           frame[0], frame[1]))
            else:
                code = gen.gi_code
                coro = ('%s() running at %s:%s'
                        % (coro_qualname, code.co_filename,
                           code.co_firstlineno))

            self.assertEqual(repr(gen), '<CoroWrapper %s>' % coro)

        # test pending Task
        t = asyncio.Task(gen, loop=self.loop)
        t.add_done_callback(Dummy())

        # format the coroutine object
        if coroutines._DEBUG:
            src = '%s:%s' % test_utils.get_function_source(notmuch)
        else:
            code = gen.gi_code
            src = '%s:%s' % (code.co_filename, code.co_firstlineno)
        coro = format_coroutine(coro_qualname, 'running', src,
                                t._source_traceback,
                                generator=not coroutines._DEBUG)
        self.assertEqual(repr(t),
                         '<Task pending %s cb=[<Dummy>()]>' % coro)
        self.loop.run_until_complete(t)

    def test_task_repr_wait_for(self):
        self.loop.set_debug(False)

        @asyncio.coroutine
        def wait_for(fut):
            return (yield from fut)

        fut = asyncio.Future(loop=self.loop)
        task = asyncio.Task(wait_for(fut), loop=self.loop)
        test_utils.run_briefly(self.loop)
        self.assertRegex(repr(task),
                         '<Task .* wait_for=%s>' % re.escape(repr(fut)))

        fut.set_result(None)
        self.loop.run_until_complete(task)

    def test_task_repr_partial_corowrapper(self):
        # Issue #222: repr(CoroWrapper) must not fail in debug mode if the
        # coroutine is a partial function
        with set_coroutine_debug(True):
            self.loop.set_debug(True)

            @asyncio.coroutine
            def func(x, y):
                yield from asyncio.sleep(0)

            partial_func = asyncio.coroutine(functools.partial(func, 1))
            task = self.loop.create_task(partial_func(2))

            # make warnings quiet
            task._log_destroy_pending = False
            self.addCleanup(task._coro.close)

        coro_repr = repr(task._coro)
        expected = ('<CoroWrapper TaskTests.test_task_repr_partial_corowrapper'
                    '.<locals>.func(1)() running, ')
        self.assertTrue(coro_repr.startswith(expected),
                        coro_repr)

    def test_task_basics(self):
        @asyncio.coroutine
        def outer():
            a = yield from inner1()
            b = yield from inner2()
            return a+b

        @asyncio.coroutine
        def inner1():
            return 42

        @asyncio.coroutine
        def inner2():
            return 1000

        t = outer()
        self.assertEqual(self.loop.run_until_complete(t), 1042)

    def test_cancel(self):

        def gen():
            when = yield
            self.assertAlmostEqual(10.0, when)
            yield 0

        loop = self.new_test_loop(gen)

        @asyncio.coroutine
        def task():
            yield from asyncio.sleep(10.0, loop=loop)
            return 12

        t = asyncio.Task(task(), loop=loop)
        loop.call_soon(t.cancel)
        with self.assertRaises(asyncio.CancelledError):
            loop.run_until_complete(t)
        self.assertTrue(t.done())
        self.assertTrue(t.cancelled())
        self.assertFalse(t.cancel())

    def test_cancel_yield(self):
        @asyncio.coroutine
        def task():
            yield
            yield
            return 12

        t = asyncio.Task(task(), loop=self.loop)
        test_utils.run_briefly(self.loop)  # start coro
        t.cancel()
        self.assertRaises(
            asyncio.CancelledError, self.loop.run_until_complete, t)
        self.assertTrue(t.done())
        self.assertTrue(t.cancelled())
        self.assertFalse(t.cancel())

    def test_cancel_inner_future(self):
        f = asyncio.Future(loop=self.loop)

        @asyncio.coroutine
        def task():
            yield from f
            return 12

        t = asyncio.Task(task(), loop=self.loop)
        test_utils.run_briefly(self.loop)  # start task
        f.cancel()
        with self.assertRaises(asyncio.CancelledError):
            self.loop.run_until_complete(t)
        self.assertTrue(f.cancelled())
        self.assertTrue(t.cancelled())

    def test_cancel_both_task_and_inner_future(self):
        f = asyncio.Future(loop=self.loop)

        @asyncio.coroutine
        def task():
            yield from f
            return 12

        t = asyncio.Task(task(), loop=self.loop)
        test_utils.run_briefly(self.loop)

        f.cancel()
        t.cancel()

        with self.assertRaises(asyncio.CancelledError):
            self.loop.run_until_complete(t)

        self.assertTrue(t.done())
        self.assertTrue(f.cancelled())
        self.assertTrue(t.cancelled())

    def test_cancel_task_catching(self):
        fut1 = asyncio.Future(loop=self.loop)
        fut2 = asyncio.Future(loop=self.loop)

        @asyncio.coroutine
        def task():
            yield from fut1
            try:
                yield from fut2
            except asyncio.CancelledError:
                return 42

        t = asyncio.Task(task(), loop=self.loop)
        test_utils.run_briefly(self.loop)
        self.assertIs(t._fut_waiter, fut1)  # White-box test.
        fut1.set_result(None)
        test_utils.run_briefly(self.loop)
        self.assertIs(t._fut_waiter, fut2)  # White-box test.
        t.cancel()
        self.assertTrue(fut2.cancelled())
        res = self.loop.run_until_complete(t)
        self.assertEqual(res, 42)
        self.assertFalse(t.cancelled())

    def test_cancel_task_ignoring(self):
        fut1 = asyncio.Future(loop=self.loop)
        fut2 = asyncio.Future(loop=self.loop)
        fut3 = asyncio.Future(loop=self.loop)

        @asyncio.coroutine
        def task():
            yield from fut1
            try:
                yield from fut2
            except asyncio.CancelledError:
                pass
            res = yield from fut3
            return res

        t = asyncio.Task(task(), loop=self.loop)
        test_utils.run_briefly(self.loop)
        self.assertIs(t._fut_waiter, fut1)  # White-box test.
        fut1.set_result(None)
        test_utils.run_briefly(self.loop)
        self.assertIs(t._fut_waiter, fut2)  # White-box test.
        t.cancel()
        self.assertTrue(fut2.cancelled())
        test_utils.run_briefly(self.loop)
        self.assertIs(t._fut_waiter, fut3)  # White-box test.
        fut3.set_result(42)
        res = self.loop.run_until_complete(t)
        self.assertEqual(res, 42)
        self.assertFalse(fut3.cancelled())
        self.assertFalse(t.cancelled())

    def test_cancel_current_task(self):
        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        @asyncio.coroutine
        def task():
            t.cancel()
            self.assertTrue(t._must_cancel)  # White-box test.
            # The sleep should be cancelled immediately.
            yield from asyncio.sleep(100, loop=loop)
            return 12

        t = asyncio.Task(task(), loop=loop)
        self.assertRaises(
            asyncio.CancelledError, loop.run_until_complete, t)
        self.assertTrue(t.done())
        self.assertFalse(t._must_cancel)  # White-box test.
        self.assertFalse(t.cancel())

    def test_stop_while_run_in_complete(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0.1
            self.assertAlmostEqual(0.2, when)
            when = yield 0.1
            self.assertAlmostEqual(0.3, when)
            yield 0.1

        loop = self.new_test_loop(gen)

        x = 0
        waiters = []

        @asyncio.coroutine
        def task():
            nonlocal x
            while x < 10:
                waiters.append(asyncio.sleep(0.1, loop=loop))
                yield from waiters[-1]
                x += 1
                if x == 2:
                    loop.stop()

        t = asyncio.Task(task(), loop=loop)
        with self.assertRaises(RuntimeError) as cm:
            loop.run_until_complete(t)
        self.assertEqual(str(cm.exception),
                         'Event loop stopped before Future completed.')
        self.assertFalse(t.done())
        self.assertEqual(x, 2)
        self.assertAlmostEqual(0.3, loop.time())

        # close generators
        for w in waiters:
            w.close()
        t.cancel()
        self.assertRaises(asyncio.CancelledError, loop.run_until_complete, t)

    def test_wait_for(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.2, when)
            when = yield 0
            self.assertAlmostEqual(0.1, when)
            when = yield 0.1

        loop = self.new_test_loop(gen)

        foo_running = None

        @asyncio.coroutine
        def foo():
            nonlocal foo_running
            foo_running = True
            try:
                yield from asyncio.sleep(0.2, loop=loop)
            finally:
                foo_running = False
            return 'done'

        fut = asyncio.Task(foo(), loop=loop)

        with self.assertRaises(asyncio.TimeoutError):
            loop.run_until_complete(asyncio.wait_for(fut, 0.1, loop=loop))
        self.assertTrue(fut.done())
        # it should have been cancelled due to the timeout
        self.assertTrue(fut.cancelled())
        self.assertAlmostEqual(0.1, loop.time())
        self.assertEqual(foo_running, False)

    def test_wait_for_blocking(self):
        loop = self.new_test_loop()

        @asyncio.coroutine
        def coro():
            return 'done'

        res = loop.run_until_complete(asyncio.wait_for(coro(),
                                                       timeout=None,
                                                       loop=loop))
        self.assertEqual(res, 'done')

    def test_wait_for_with_global_loop(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.2, when)
            when = yield 0
            self.assertAlmostEqual(0.01, when)
            yield 0.01

        loop = self.new_test_loop(gen)

        @asyncio.coroutine
        def foo():
            yield from asyncio.sleep(0.2, loop=loop)
            return 'done'

        asyncio.set_event_loop(loop)
        try:
            fut = asyncio.Task(foo(), loop=loop)
            with self.assertRaises(asyncio.TimeoutError):
                loop.run_until_complete(asyncio.wait_for(fut, 0.01))
        finally:
            asyncio.set_event_loop(None)

        self.assertAlmostEqual(0.01, loop.time())
        self.assertTrue(fut.done())
        self.assertTrue(fut.cancelled())

    def test_wait_for_race_condition(self):

        def gen():
            yield 0.1
            yield 0.1
            yield 0.1

        loop = self.new_test_loop(gen)

        fut = asyncio.Future(loop=loop)
        task = asyncio.wait_for(fut, timeout=0.2, loop=loop)
        loop.call_later(0.1, fut.set_result, "ok")
        res = loop.run_until_complete(task)
        self.assertEqual(res, "ok")

    def test_wait(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0
            self.assertAlmostEqual(0.15, when)
            yield 0.15

        loop = self.new_test_loop(gen)

        a = asyncio.Task(asyncio.sleep(0.1, loop=loop), loop=loop)
        b = asyncio.Task(asyncio.sleep(0.15, loop=loop), loop=loop)

        @asyncio.coroutine
        def foo():
            done, pending = yield from asyncio.wait([b, a], loop=loop)
            self.assertEqual(done, set([a, b]))
            self.assertEqual(pending, set())
            return 42

        res = loop.run_until_complete(asyncio.Task(foo(), loop=loop))
        self.assertEqual(res, 42)
        self.assertAlmostEqual(0.15, loop.time())

        # Doing it again should take no time and exercise a different path.
        res = loop.run_until_complete(asyncio.Task(foo(), loop=loop))
        self.assertAlmostEqual(0.15, loop.time())
        self.assertEqual(res, 42)

    def test_wait_with_global_loop(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.01, when)
            when = yield 0
            self.assertAlmostEqual(0.015, when)
            yield 0.015

        loop = self.new_test_loop(gen)

        a = asyncio.Task(asyncio.sleep(0.01, loop=loop), loop=loop)
        b = asyncio.Task(asyncio.sleep(0.015, loop=loop), loop=loop)

        @asyncio.coroutine
        def foo():
            done, pending = yield from asyncio.wait([b, a])
            self.assertEqual(done, set([a, b]))
            self.assertEqual(pending, set())
            return 42

        asyncio.set_event_loop(loop)
        res = loop.run_until_complete(
            asyncio.Task(foo(), loop=loop))

        self.assertEqual(res, 42)

    def test_wait_duplicate_coroutines(self):
        @asyncio.coroutine
        def coro(s):
            return s
        c = coro('test')

        task = asyncio.Task(
            asyncio.wait([c, c, coro('spam')], loop=self.loop),
            loop=self.loop)

        done, pending = self.loop.run_until_complete(task)

        self.assertFalse(pending)
        self.assertEqual(set(f.result() for f in done), {'test', 'spam'})

    def test_wait_errors(self):
        self.assertRaises(
            ValueError, self.loop.run_until_complete,
            asyncio.wait(set(), loop=self.loop))

        # -1 is an invalid return_when value
        sleep_coro = asyncio.sleep(10.0, loop=self.loop)
        wait_coro = asyncio.wait([sleep_coro], return_when=-1, loop=self.loop)
        self.assertRaises(ValueError,
                          self.loop.run_until_complete, wait_coro)

        sleep_coro.close()

    def test_wait_first_completed(self):

        def gen():
            when = yield
            self.assertAlmostEqual(10.0, when)
            when = yield 0
            self.assertAlmostEqual(0.1, when)
            yield 0.1

        loop = self.new_test_loop(gen)

        a = asyncio.Task(asyncio.sleep(10.0, loop=loop), loop=loop)
        b = asyncio.Task(asyncio.sleep(0.1, loop=loop), loop=loop)
        task = asyncio.Task(
            asyncio.wait([b, a], return_when=asyncio.FIRST_COMPLETED,
                         loop=loop),
            loop=loop)

        done, pending = loop.run_until_complete(task)
        self.assertEqual({b}, done)
        self.assertEqual({a}, pending)
        self.assertFalse(a.done())
        self.assertTrue(b.done())
        self.assertIsNone(b.result())
        self.assertAlmostEqual(0.1, loop.time())

        # move forward to close generator
        loop.advance_time(10)
        loop.run_until_complete(asyncio.wait([a, b], loop=loop))

    def test_wait_really_done(self):
        # there is possibility that some tasks in the pending list
        # became done but their callbacks haven't all been called yet

        @asyncio.coroutine
        def coro1():
            yield

        @asyncio.coroutine
        def coro2():
            yield
            yield

        a = asyncio.Task(coro1(), loop=self.loop)
        b = asyncio.Task(coro2(), loop=self.loop)
        task = asyncio.Task(
            asyncio.wait([b, a], return_when=asyncio.FIRST_COMPLETED,
                         loop=self.loop),
            loop=self.loop)

        done, pending = self.loop.run_until_complete(task)
        self.assertEqual({a, b}, done)
        self.assertTrue(a.done())
        self.assertIsNone(a.result())
        self.assertTrue(b.done())
        self.assertIsNone(b.result())

    def test_wait_first_exception(self):

        def gen():
            when = yield
            self.assertAlmostEqual(10.0, when)
            yield 0

        loop = self.new_test_loop(gen)

        # first_exception, task already has exception
        a = asyncio.Task(asyncio.sleep(10.0, loop=loop), loop=loop)

        @asyncio.coroutine
        def exc():
            raise ZeroDivisionError('err')

        b = asyncio.Task(exc(), loop=loop)
        task = asyncio.Task(
            asyncio.wait([b, a], return_when=asyncio.FIRST_EXCEPTION,
                         loop=loop),
            loop=loop)

        done, pending = loop.run_until_complete(task)
        self.assertEqual({b}, done)
        self.assertEqual({a}, pending)
        self.assertAlmostEqual(0, loop.time())

        # move forward to close generator
        loop.advance_time(10)
        loop.run_until_complete(asyncio.wait([a, b], loop=loop))

    def test_wait_first_exception_in_wait(self):

        def gen():
            when = yield
            self.assertAlmostEqual(10.0, when)
            when = yield 0
            self.assertAlmostEqual(0.01, when)
            yield 0.01

        loop = self.new_test_loop(gen)

        # first_exception, exception during waiting
        a = asyncio.Task(asyncio.sleep(10.0, loop=loop), loop=loop)

        @asyncio.coroutine
        def exc():
            yield from asyncio.sleep(0.01, loop=loop)
            raise ZeroDivisionError('err')

        b = asyncio.Task(exc(), loop=loop)
        task = asyncio.wait([b, a], return_when=asyncio.FIRST_EXCEPTION,
                            loop=loop)

        done, pending = loop.run_until_complete(task)
        self.assertEqual({b}, done)
        self.assertEqual({a}, pending)
        self.assertAlmostEqual(0.01, loop.time())

        # move forward to close generator
        loop.advance_time(10)
        loop.run_until_complete(asyncio.wait([a, b], loop=loop))

    def test_wait_with_exception(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0
            self.assertAlmostEqual(0.15, when)
            yield 0.15

        loop = self.new_test_loop(gen)

        a = asyncio.Task(asyncio.sleep(0.1, loop=loop), loop=loop)

        @asyncio.coroutine
        def sleeper():
            yield from asyncio.sleep(0.15, loop=loop)
            raise ZeroDivisionError('really')

        b = asyncio.Task(sleeper(), loop=loop)

        @asyncio.coroutine
        def foo():
            done, pending = yield from asyncio.wait([b, a], loop=loop)
            self.assertEqual(len(done), 2)
            self.assertEqual(pending, set())
            errors = set(f for f in done if f.exception() is not None)
            self.assertEqual(len(errors), 1)

        loop.run_until_complete(asyncio.Task(foo(), loop=loop))
        self.assertAlmostEqual(0.15, loop.time())

        loop.run_until_complete(asyncio.Task(foo(), loop=loop))
        self.assertAlmostEqual(0.15, loop.time())

    def test_wait_with_timeout(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0
            self.assertAlmostEqual(0.15, when)
            when = yield 0
            self.assertAlmostEqual(0.11, when)
            yield 0.11

        loop = self.new_test_loop(gen)

        a = asyncio.Task(asyncio.sleep(0.1, loop=loop), loop=loop)
        b = asyncio.Task(asyncio.sleep(0.15, loop=loop), loop=loop)

        @asyncio.coroutine
        def foo():
            done, pending = yield from asyncio.wait([b, a], timeout=0.11,
                                                    loop=loop)
            self.assertEqual(done, set([a]))
            self.assertEqual(pending, set([b]))

        loop.run_until_complete(asyncio.Task(foo(), loop=loop))
        self.assertAlmostEqual(0.11, loop.time())

        # move forward to close generator
        loop.advance_time(10)
        loop.run_until_complete(asyncio.wait([a, b], loop=loop))

    def test_wait_concurrent_complete(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0
            self.assertAlmostEqual(0.15, when)
            when = yield 0
            self.assertAlmostEqual(0.1, when)
            yield 0.1

        loop = self.new_test_loop(gen)

        a = asyncio.Task(asyncio.sleep(0.1, loop=loop), loop=loop)
        b = asyncio.Task(asyncio.sleep(0.15, loop=loop), loop=loop)

        done, pending = loop.run_until_complete(
            asyncio.wait([b, a], timeout=0.1, loop=loop))

        self.assertEqual(done, set([a]))
        self.assertEqual(pending, set([b]))
        self.assertAlmostEqual(0.1, loop.time())

        # move forward to close generator
        loop.advance_time(10)
        loop.run_until_complete(asyncio.wait([a, b], loop=loop))

    def test_as_completed(self):

        def gen():
            yield 0
            yield 0
            yield 0.01
            yield 0

        loop = self.new_test_loop(gen)
        # disable "slow callback" warning
        loop.slow_callback_duration = 1.0
        completed = set()
        time_shifted = False

        @asyncio.coroutine
        def sleeper(dt, x):
            nonlocal time_shifted
            yield from asyncio.sleep(dt, loop=loop)
            completed.add(x)
            if not time_shifted and 'a' in completed and 'b' in completed:
                time_shifted = True
                loop.advance_time(0.14)
            return x

        a = sleeper(0.01, 'a')
        b = sleeper(0.01, 'b')
        c = sleeper(0.15, 'c')

        @asyncio.coroutine
        def foo():
            values = []
            for f in asyncio.as_completed([b, c, a], loop=loop):
                values.append((yield from f))
            return values

        res = loop.run_until_complete(asyncio.Task(foo(), loop=loop))
        self.assertAlmostEqual(0.15, loop.time())
        self.assertTrue('a' in res[:2])
        self.assertTrue('b' in res[:2])
        self.assertEqual(res[2], 'c')

        # Doing it again should take no time and exercise a different path.
        res = loop.run_until_complete(asyncio.Task(foo(), loop=loop))
        self.assertAlmostEqual(0.15, loop.time())

    def test_as_completed_with_timeout(self):

        def gen():
            yield
            yield 0
            yield 0
            yield 0.1

        loop = self.new_test_loop(gen)

        a = asyncio.sleep(0.1, 'a', loop=loop)
        b = asyncio.sleep(0.15, 'b', loop=loop)

        @asyncio.coroutine
        def foo():
            values = []
            for f in asyncio.as_completed([a, b], timeout=0.12, loop=loop):
                if values:
                    loop.advance_time(0.02)
                try:
                    v = yield from f
                    values.append((1, v))
                except asyncio.TimeoutError as exc:
                    values.append((2, exc))
            return values

        res = loop.run_until_complete(asyncio.Task(foo(), loop=loop))
        self.assertEqual(len(res), 2, res)
        self.assertEqual(res[0], (1, 'a'))
        self.assertEqual(res[1][0], 2)
        self.assertIsInstance(res[1][1], asyncio.TimeoutError)
        self.assertAlmostEqual(0.12, loop.time())

        # move forward to close generator
        loop.advance_time(10)
        loop.run_until_complete(asyncio.wait([a, b], loop=loop))

    def test_as_completed_with_unused_timeout(self):

        def gen():
            yield
            yield 0
            yield 0.01

        loop = self.new_test_loop(gen)

        a = asyncio.sleep(0.01, 'a', loop=loop)

        @asyncio.coroutine
        def foo():
            for f in asyncio.as_completed([a], timeout=1, loop=loop):
                v = yield from f
                self.assertEqual(v, 'a')

        loop.run_until_complete(asyncio.Task(foo(), loop=loop))

    def test_as_completed_reverse_wait(self):

        def gen():
            yield 0
            yield 0.05
            yield 0

        loop = self.new_test_loop(gen)

        a = asyncio.sleep(0.05, 'a', loop=loop)
        b = asyncio.sleep(0.10, 'b', loop=loop)
        fs = {a, b}
        futs = list(asyncio.as_completed(fs, loop=loop))
        self.assertEqual(len(futs), 2)

        x = loop.run_until_complete(futs[1])
        self.assertEqual(x, 'a')
        self.assertAlmostEqual(0.05, loop.time())
        loop.advance_time(0.05)
        y = loop.run_until_complete(futs[0])
        self.assertEqual(y, 'b')
        self.assertAlmostEqual(0.10, loop.time())

    def test_as_completed_concurrent(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.05, when)
            when = yield 0
            self.assertAlmostEqual(0.05, when)
            yield 0.05

        loop = self.new_test_loop(gen)

        a = asyncio.sleep(0.05, 'a', loop=loop)
        b = asyncio.sleep(0.05, 'b', loop=loop)
        fs = {a, b}
        futs = list(asyncio.as_completed(fs, loop=loop))
        self.assertEqual(len(futs), 2)
        waiter = asyncio.wait(futs, loop=loop)
        done, pending = loop.run_until_complete(waiter)
        self.assertEqual(set(f.result() for f in done), {'a', 'b'})

    def test_as_completed_duplicate_coroutines(self):

        @asyncio.coroutine
        def coro(s):
            return s

        @asyncio.coroutine
        def runner():
            result = []
            c = coro('ham')
            for f in asyncio.as_completed([c, c, coro('spam')],
                                          loop=self.loop):
                result.append((yield from f))
            return result

        fut = asyncio.Task(runner(), loop=self.loop)
        self.loop.run_until_complete(fut)
        result = fut.result()
        self.assertEqual(set(result), {'ham', 'spam'})
        self.assertEqual(len(result), 2)

    def test_sleep(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.05, when)
            when = yield 0.05
            self.assertAlmostEqual(0.1, when)
            yield 0.05

        loop = self.new_test_loop(gen)

        @asyncio.coroutine
        def sleeper(dt, arg):
            yield from asyncio.sleep(dt/2, loop=loop)
            res = yield from asyncio.sleep(dt/2, arg, loop=loop)
            return res

        t = asyncio.Task(sleeper(0.1, 'yeah'), loop=loop)
        loop.run_until_complete(t)
        self.assertTrue(t.done())
        self.assertEqual(t.result(), 'yeah')
        self.assertAlmostEqual(0.1, loop.time())

    def test_sleep_cancel(self):

        def gen():
            when = yield
            self.assertAlmostEqual(10.0, when)
            yield 0

        loop = self.new_test_loop(gen)

        t = asyncio.Task(asyncio.sleep(10.0, 'yeah', loop=loop),
                         loop=loop)

        handle = None
        orig_call_later = loop.call_later

        def call_later(delay, callback, *args):
            nonlocal handle
            handle = orig_call_later(delay, callback, *args)
            return handle

        loop.call_later = call_later
        test_utils.run_briefly(loop)

        self.assertFalse(handle._cancelled)

        t.cancel()
        test_utils.run_briefly(loop)
        self.assertTrue(handle._cancelled)

    def test_task_cancel_sleeping_task(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0
            self.assertAlmostEqual(5000, when)
            yield 0.1

        loop = self.new_test_loop(gen)

        @asyncio.coroutine
        def sleep(dt):
            yield from asyncio.sleep(dt, loop=loop)

        @asyncio.coroutine
        def doit():
            sleeper = asyncio.Task(sleep(5000), loop=loop)
            loop.call_later(0.1, sleeper.cancel)
            try:
                yield from sleeper
            except asyncio.CancelledError:
                return 'cancelled'
            else:
                return 'slept in'

        doer = doit()
        self.assertEqual(loop.run_until_complete(doer), 'cancelled')
        self.assertAlmostEqual(0.1, loop.time())

    def test_task_cancel_waiter_future(self):
        fut = asyncio.Future(loop=self.loop)

        @asyncio.coroutine
        def coro():
            yield from fut

        task = asyncio.Task(coro(), loop=self.loop)
        test_utils.run_briefly(self.loop)
        self.assertIs(task._fut_waiter, fut)

        task.cancel()
        test_utils.run_briefly(self.loop)
        self.assertRaises(
            asyncio.CancelledError, self.loop.run_until_complete, task)
        self.assertIsNone(task._fut_waiter)
        self.assertTrue(fut.cancelled())

    def test_step_in_completed_task(self):
        @asyncio.coroutine
        def notmuch():
            return 'ko'

        gen = notmuch()
        task = asyncio.Task(gen, loop=self.loop)
        task.set_result('ok')

        self.assertRaises(AssertionError, task._step)
        gen.close()

    def test_step_result(self):
        @asyncio.coroutine
        def notmuch():
            yield None
            yield 1
            return 'ko'

        self.assertRaises(
            RuntimeError, self.loop.run_until_complete, notmuch())

    def test_step_result_future(self):
        # If coroutine returns future, task waits on this future.

        class Fut(asyncio.Future):
            def __init__(self, *args, **kwds):
                self.cb_added = False
                super().__init__(*args, **kwds)

            def add_done_callback(self, fn):
                self.cb_added = True
                super().add_done_callback(fn)

        fut = Fut(loop=self.loop)
        result = None

        @asyncio.coroutine
        def wait_for_future():
            nonlocal result
            result = yield from fut

        t = asyncio.Task(wait_for_future(), loop=self.loop)
        test_utils.run_briefly(self.loop)
        self.assertTrue(fut.cb_added)

        res = object()
        fut.set_result(res)
        test_utils.run_briefly(self.loop)
        self.assertIs(res, result)
        self.assertTrue(t.done())
        self.assertIsNone(t.result())

    def test_step_with_baseexception(self):
        @asyncio.coroutine
        def notmutch():
            raise BaseException()

        task = asyncio.Task(notmutch(), loop=self.loop)
        self.assertRaises(BaseException, task._step)

        self.assertTrue(task.done())
        self.assertIsInstance(task.exception(), BaseException)

    def test_baseexception_during_cancel(self):

        def gen():
            when = yield
            self.assertAlmostEqual(10.0, when)
            yield 0

        loop = self.new_test_loop(gen)

        @asyncio.coroutine
        def sleeper():
            yield from asyncio.sleep(10, loop=loop)

        base_exc = BaseException()

        @asyncio.coroutine
        def notmutch():
            try:
                yield from sleeper()
            except asyncio.CancelledError:
                raise base_exc

        task = asyncio.Task(notmutch(), loop=loop)
        test_utils.run_briefly(loop)

        task.cancel()
        self.assertFalse(task.done())

        self.assertRaises(BaseException, test_utils.run_briefly, loop)

        self.assertTrue(task.done())
        self.assertFalse(task.cancelled())
        self.assertIs(task.exception(), base_exc)

    def test_iscoroutinefunction(self):
        def fn():
            pass

        self.assertFalse(asyncio.iscoroutinefunction(fn))

        def fn1():
            yield
        self.assertFalse(asyncio.iscoroutinefunction(fn1))

        @asyncio.coroutine
        def fn2():
            yield
        self.assertTrue(asyncio.iscoroutinefunction(fn2))

    def test_yield_vs_yield_from(self):
        fut = asyncio.Future(loop=self.loop)

        @asyncio.coroutine
        def wait_for_future():
            yield fut

        task = wait_for_future()
        with self.assertRaises(RuntimeError):
            self.loop.run_until_complete(task)

        self.assertFalse(fut.done())

    def test_yield_vs_yield_from_generator(self):
        @asyncio.coroutine
        def coro():
            yield

        @asyncio.coroutine
        def wait_for_future():
            gen = coro()
            try:
                yield gen
            finally:
                gen.close()

        task = wait_for_future()
        self.assertRaises(
            RuntimeError,
            self.loop.run_until_complete, task)

    def test_coroutine_non_gen_function(self):
        @asyncio.coroutine
        def func():
            return 'test'

        self.assertTrue(asyncio.iscoroutinefunction(func))

        coro = func()
        self.assertTrue(asyncio.iscoroutine(coro))

        res = self.loop.run_until_complete(coro)
        self.assertEqual(res, 'test')

    def test_coroutine_non_gen_function_return_future(self):
        fut = asyncio.Future(loop=self.loop)

        @asyncio.coroutine
        def func():
            return fut

        @asyncio.coroutine
        def coro():
            fut.set_result('test')

        t1 = asyncio.Task(func(), loop=self.loop)
        t2 = asyncio.Task(coro(), loop=self.loop)
        res = self.loop.run_until_complete(t1)
        self.assertEqual(res, 'test')
        self.assertIsNone(t2.result())

    def test_current_task(self):
        self.assertIsNone(asyncio.Task.current_task(loop=self.loop))

        @asyncio.coroutine
        def coro(loop):
            self.assertTrue(asyncio.Task.current_task(loop=loop) is task)

        task = asyncio.Task(coro(self.loop), loop=self.loop)
        self.loop.run_until_complete(task)
        self.assertIsNone(asyncio.Task.current_task(loop=self.loop))

    def test_current_task_with_interleaving_tasks(self):
        self.assertIsNone(asyncio.Task.current_task(loop=self.loop))

        fut1 = asyncio.Future(loop=self.loop)
        fut2 = asyncio.Future(loop=self.loop)

        @asyncio.coroutine
        def coro1(loop):
            self.assertTrue(asyncio.Task.current_task(loop=loop) is task1)
            yield from fut1
            self.assertTrue(asyncio.Task.current_task(loop=loop) is task1)
            fut2.set_result(True)

        @asyncio.coroutine
        def coro2(loop):
            self.assertTrue(asyncio.Task.current_task(loop=loop) is task2)
            fut1.set_result(True)
            yield from fut2
            self.assertTrue(asyncio.Task.current_task(loop=loop) is task2)

        task1 = asyncio.Task(coro1(self.loop), loop=self.loop)
        task2 = asyncio.Task(coro2(self.loop), loop=self.loop)

        self.loop.run_until_complete(asyncio.wait((task1, task2),
                                                  loop=self.loop))
        self.assertIsNone(asyncio.Task.current_task(loop=self.loop))

    # Some thorough tests for cancellation propagation through
    # coroutines, tasks and wait().

    def test_yield_future_passes_cancel(self):
        # Cancelling outer() cancels inner() cancels waiter.
        proof = 0
        waiter = asyncio.Future(loop=self.loop)

        @asyncio.coroutine
        def inner():
            nonlocal proof
            try:
                yield from waiter
            except asyncio.CancelledError:
                proof += 1
                raise
            else:
                self.fail('got past sleep() in inner()')

        @asyncio.coroutine
        def outer():
            nonlocal proof
            try:
                yield from inner()
            except asyncio.CancelledError:
                proof += 100  # Expect this path.
            else:
                proof += 10

        f = asyncio.ensure_future(outer(), loop=self.loop)
        test_utils.run_briefly(self.loop)
        f.cancel()
        self.loop.run_until_complete(f)
        self.assertEqual(proof, 101)
        self.assertTrue(waiter.cancelled())

    def test_yield_wait_does_not_shield_cancel(self):
        # Cancelling outer() makes wait() return early, leaves inner()
        # running.
        proof = 0
        waiter = asyncio.Future(loop=self.loop)

        @asyncio.coroutine
        def inner():
            nonlocal proof
            yield from waiter
            proof += 1

        @asyncio.coroutine
        def outer():
            nonlocal proof
            d, p = yield from asyncio.wait([inner()], loop=self.loop)
            proof += 100

        f = asyncio.ensure_future(outer(), loop=self.loop)
        test_utils.run_briefly(self.loop)
        f.cancel()
        self.assertRaises(
            asyncio.CancelledError, self.loop.run_until_complete, f)
        waiter.set_result(None)
        test_utils.run_briefly(self.loop)
        self.assertEqual(proof, 1)

    def test_shield_result(self):
        inner = asyncio.Future(loop=self.loop)
        outer = asyncio.shield(inner)
        inner.set_result(42)
        res = self.loop.run_until_complete(outer)
        self.assertEqual(res, 42)

    def test_shield_exception(self):
        inner = asyncio.Future(loop=self.loop)
        outer = asyncio.shield(inner)
        test_utils.run_briefly(self.loop)
        exc = RuntimeError('expected')
        inner.set_exception(exc)
        test_utils.run_briefly(self.loop)
        self.assertIs(outer.exception(), exc)

    def test_shield_cancel(self):
        inner = asyncio.Future(loop=self.loop)
        outer = asyncio.shield(inner)
        test_utils.run_briefly(self.loop)
        inner.cancel()
        test_utils.run_briefly(self.loop)
        self.assertTrue(outer.cancelled())

    def test_shield_shortcut(self):
        fut = asyncio.Future(loop=self.loop)
        fut.set_result(42)
        res = self.loop.run_until_complete(asyncio.shield(fut))
        self.assertEqual(res, 42)

    def test_shield_effect(self):
        # Cancelling outer() does not affect inner().
        proof = 0
        waiter = asyncio.Future(loop=self.loop)

        @asyncio.coroutine
        def inner():
            nonlocal proof
            yield from waiter
            proof += 1

        @asyncio.coroutine
        def outer():
            nonlocal proof
            yield from asyncio.shield(inner(), loop=self.loop)
            proof += 100

        f = asyncio.ensure_future(outer(), loop=self.loop)
        test_utils.run_briefly(self.loop)
        f.cancel()
        with self.assertRaises(asyncio.CancelledError):
            self.loop.run_until_complete(f)
        waiter.set_result(None)
        test_utils.run_briefly(self.loop)
        self.assertEqual(proof, 1)

    def test_shield_gather(self):
        child1 = asyncio.Future(loop=self.loop)
        child2 = asyncio.Future(loop=self.loop)
        parent = asyncio.gather(child1, child2, loop=self.loop)
        outer = asyncio.shield(parent, loop=self.loop)
        test_utils.run_briefly(self.loop)
        outer.cancel()
        test_utils.run_briefly(self.loop)
        self.assertTrue(outer.cancelled())
        child1.set_result(1)
        child2.set_result(2)
        test_utils.run_briefly(self.loop)
        self.assertEqual(parent.result(), [1, 2])

    def test_gather_shield(self):
        child1 = asyncio.Future(loop=self.loop)
        child2 = asyncio.Future(loop=self.loop)
        inner1 = asyncio.shield(child1, loop=self.loop)
        inner2 = asyncio.shield(child2, loop=self.loop)
        parent = asyncio.gather(inner1, inner2, loop=self.loop)
        test_utils.run_briefly(self.loop)
        parent.cancel()
        # This should cancel inner1 and inner2 but bot child1 and child2.
        test_utils.run_briefly(self.loop)
        self.assertIsInstance(parent.exception(), asyncio.CancelledError)
        self.assertTrue(inner1.cancelled())
        self.assertTrue(inner2.cancelled())
        child1.set_result(1)
        child2.set_result(2)
        test_utils.run_briefly(self.loop)

    def test_as_completed_invalid_args(self):
        fut = asyncio.Future(loop=self.loop)

        # as_completed() expects a list of futures, not a future instance
        self.assertRaises(TypeError, self.loop.run_until_complete,
            asyncio.as_completed(fut, loop=self.loop))
        coro = coroutine_function()
        self.assertRaises(TypeError, self.loop.run_until_complete,
            asyncio.as_completed(coro, loop=self.loop))
        coro.close()

    def test_wait_invalid_args(self):
        fut = asyncio.Future(loop=self.loop)

        # wait() expects a list of futures, not a future instance
        self.assertRaises(TypeError, self.loop.run_until_complete,
            asyncio.wait(fut, loop=self.loop))
        coro = coroutine_function()
        self.assertRaises(TypeError, self.loop.run_until_complete,
            asyncio.wait(coro, loop=self.loop))
        coro.close()

        # wait() expects at least a future
        self.assertRaises(ValueError, self.loop.run_until_complete,
            asyncio.wait([], loop=self.loop))

    def test_corowrapper_mocks_generator(self):

        def check():
            # A function that asserts various things.
            # Called twice, with different debug flag values.

            @asyncio.coroutine
            def coro():
                # The actual coroutine.
              …