/Windows/Python3.8/WPy64-3830/WPy64-3830/python-3.8.3.amd64/Lib/asyncio/tasks.py

"""Support for tasks, coroutines and the scheduler."""



__all__ = (

    'Task', 'create_task',

    'FIRST_COMPLETED', 'FIRST_EXCEPTION', 'ALL_COMPLETED',

    'wait', 'wait_for', 'as_completed', 'sleep',

    'gather', 'shield', 'ensure_future', 'run_coroutine_threadsafe',

    'current_task', 'all_tasks',

    '_register_task', '_unregister_task', '_enter_task', '_leave_task',

)



import concurrent.futures

import contextvars

import functools

import inspect

import itertools

import types

import warnings

import weakref



from . import base_tasks

from . import coroutines

from . import events

from . import exceptions

from . import futures

from .coroutines import _is_coroutine



# Helper to generate new task names

# This uses itertools.count() instead of a "+= 1" operation because the latter

# is not thread safe. See bpo-11866 for a longer explanation.

_task_name_counter = itertools.count(1).__next__





def current_task(loop=None):

    """Return a currently executed task."""

    if loop is None:

        loop = events.get_running_loop()

    return _current_tasks.get(loop)





def all_tasks(loop=None):

    """Return a set of all tasks for the loop."""

    if loop is None:

        loop = events.get_running_loop()

    # Looping over a WeakSet (_all_tasks) isn't safe as it can be updated from another

    # thread while we do so. Therefore we cast it to list prior to filtering. The list

    # cast itself requires iteration, so we repeat it several times ignoring

    # RuntimeErrors (which are not very likely to occur). See issues 34970 and 36607 for

    # details.

    i = 0

    while True:

        try:

            tasks = list(_all_tasks)

        except RuntimeError:

            i += 1

            if i >= 1000:

                raise

        else:

            break

    return {t for t in tasks

            if futures._get_loop(t) is loop and not t.done()}





def _all_tasks_compat(loop=None):

    # Different from "all_task()" by returning *all* Tasks, including

    # the completed ones.  Used to implement deprecated "Tasks.all_task()"

    # method.

    if loop is None:

        loop = events.get_event_loop()

    # Looping over a WeakSet (_all_tasks) isn't safe as it can be updated from another

    # thread while we do so. Therefore we cast it to list prior to filtering. The list

    # cast itself requires iteration, so we repeat it several times ignoring

    # RuntimeErrors (which are not very likely to occur). See issues 34970 and 36607 for

    # details.

    i = 0

    while True:

        try:

            tasks = list(_all_tasks)

        except RuntimeError:

            i += 1

            if i >= 1000:

                raise

        else:

            break

    return {t for t in tasks if futures._get_loop(t) is loop}





def _set_task_name(task, name):

    if name is not None:

        try:

            set_name = task.set_name

        except AttributeError:

            pass

        else:

            set_name(name)





class Task(futures._PyFuture):  # Inherit Python Task implementation

                                # from a Python Future implementation.



    """A coroutine wrapped in a Future."""



    # An important invariant maintained while a Task not done:

    #

    # - Either _fut_waiter is None, and _step() is scheduled;

    # - or _fut_waiter is some Future, and _step() is *not* scheduled.

    #

    # The only transition from the latter to the former is through

    # _wakeup().  When _fut_waiter is not None, one of its callbacks

    # must be _wakeup().



    # If False, don't log a message if the task is destroyed whereas its

    # status is still pending

    _log_destroy_pending = True



    @classmethod

    def current_task(cls, loop=None):

        """Return the currently running task in an event loop or None.



        By default the current task for the current event loop is returned.



        None is returned when called not in the context of a Task.

        """

        warnings.warn("Task.current_task() is deprecated since Python 3.7, "

                      "use asyncio.current_task() instead",

                      DeprecationWarning,

                      stacklevel=2)

        if loop is None:

            loop = events.get_event_loop()

        return current_task(loop)



    @classmethod

    def all_tasks(cls, loop=None):

        """Return a set of all tasks for an event loop.



        By default all tasks for the current event loop are returned.

        """

        warnings.warn("Task.all_tasks() is deprecated since Python 3.7, "

                      "use asyncio.all_tasks() instead",

                      DeprecationWarning,

                      stacklevel=2)

        return _all_tasks_compat(loop)



    def __init__(self, coro, *, loop=None, name=None):

        super().__init__(loop=loop)

        if self._source_traceback:

            del self._source_traceback[-1]

        if not coroutines.iscoroutine(coro):

            # raise after Future.__init__(), attrs are required for __del__

            # prevent logging for pending task in __del__

            self._log_destroy_pending = False

            raise TypeError(f"a coroutine was expected, got {coro!r}")



        if name is None:

            self._name = f'Task-{_task_name_counter()}'

        else:

            self._name = str(name)



        self._must_cancel = False

        self._fut_waiter = None

        self._coro = coro

        self._context = contextvars.copy_context()



        self._loop.call_soon(self.__step, context=self._context)

        _register_task(self)



    def __del__(self):

        if self._state == futures._PENDING and self._log_destroy_pending:

            context = {

                'task': self,

                'message': 'Task was destroyed but it is pending!',

            }

            if self._source_traceback:

                context['source_traceback'] = self._source_traceback

            self._loop.call_exception_handler(context)

        super().__del__()



    def _repr_info(self):

        return base_tasks._task_repr_info(self)



    def get_coro(self):

        return self._coro



    def get_name(self):

        return self._name



    def set_name(self, value):

        self._name = str(value)



    def set_result(self, result):

        raise RuntimeError('Task does not support set_result operation')



    def set_exception(self, exception):

        raise RuntimeError('Task does not support set_exception operation')



    def get_stack(self, *, limit=None):

        """Return the list of stack frames for this task's coroutine.



        If the coroutine is not done, this returns the stack where it is

        suspended.  If the coroutine has completed successfully or was

        cancelled, this returns an empty list.  If the coroutine was

        terminated by an exception, this returns the list of traceback

        frames.



        The frames are always ordered from oldest to newest.



        The optional limit gives the maximum number of frames to

        return; by default all available frames are returned.  Its

        meaning differs depending on whether a stack or a traceback is

        returned: the newest frames of a stack are returned, but the

        oldest frames of a traceback are returned.  (This matches the

        behavior of the traceback module.)



        For reasons beyond our control, only one stack frame is

        returned for a suspended coroutine.

        """

        return base_tasks._task_get_stack(self, limit)



    def print_stack(self, *, limit=None, file=None):

        """Print the stack or traceback for this task's coroutine.



        This produces output similar to that of the traceback module,

        for the frames retrieved by get_stack().  The limit argument

        is passed to get_stack().  The file argument is an I/O stream

        to which the output is written; by default output is written

        to sys.stderr.

        """

        return base_tasks._task_print_stack(self, limit, file)



    def cancel(self):

        """Request that this task cancel itself.



        This arranges for a CancelledError to be thrown into the

        wrapped coroutine on the next cycle through the event loop.

        The coroutine then has a chance to clean up or even deny

        the request using try/except/finally.



        Unlike Future.cancel, this does not guarantee that the

        task will be cancelled: the exception might be caught and

        acted upon, delaying cancellation of the task or preventing

        cancellation completely.  The task may also return a value or

        raise a different exception.



        Immediately after this method is called, Task.cancelled() will

        not return True (unless the task was already cancelled).  A

        task will be marked as cancelled when the wrapped coroutine

        terminates with a CancelledError exception (even if cancel()

        was not called).

        """

        self._log_traceback = False

        if self.done():

            return False

        if self._fut_waiter is not None:

            if self._fut_waiter.cancel():

                # Leave self._fut_waiter; it may be a Task that

                # catches and ignores the cancellation so we may have

                # to cancel it again later.

                return True

        # It must be the case that self.__step is already scheduled.

        self._must_cancel = True

        return True



    def __step(self, exc=None):

        if self.done():

            raise exceptions.InvalidStateError(

                f'_step(): already done: {self!r}, {exc!r}')

        if self._must_cancel:

            if not isinstance(exc, exceptions.CancelledError):

                exc = exceptions.CancelledError()

            self._must_cancel = False

        coro = self._coro

        self._fut_waiter = None



        _enter_task(self._loop, self)

        # Call either coro.throw(exc) or coro.send(None).

        try:

            if exc is None:

                # We use the `send` method directly, because coroutines

                # don't have `__iter__` and `__next__` methods.

                result = coro.send(None)

            else:

                result = coro.throw(exc)

        except StopIteration as exc:

            if self._must_cancel:

                # Task is cancelled right before coro stops.

                self._must_cancel = False

                super().cancel()

            else:

                super().set_result(exc.value)

        except exceptions.CancelledError:

            super().cancel()  # I.e., Future.cancel(self).

        except (KeyboardInterrupt, SystemExit) as exc:

            super().set_exception(exc)

            raise

        except BaseException as exc:

            super().set_exception(exc)

        else:

            blocking = getattr(result, '_asyncio_future_blocking', None)

            if blocking is not None:

                # Yielded Future must come from Future.__iter__().

                if futures._get_loop(result) is not self._loop:

                    new_exc = RuntimeError(

                        f'Task {self!r} got Future '

                        f'{result!r} attached to a different loop')

                    self._loop.call_soon(

                        self.__step, new_exc, context=self._context)

                elif blocking:

                    if result is self:

                        new_exc = RuntimeError(

                            f'Task cannot await on itself: {self!r}')

                        self._loop.call_soon(

                            self.__step, new_exc, context=self._context)

                    else:

                        result._asyncio_future_blocking = False

                        result.add_done_callback(

                            self.__wakeup, context=self._context)

                        self._fut_waiter = result

                        if self._must_cancel:

                            if self._fut_waiter.cancel():

                                self._must_cancel = False

                else:

                    new_exc = RuntimeError(

                        f'yield was used instead of yield from '

                        f'in task {self!r} with {result!r}')

                    self._loop.call_soon(

                        self.__step, new_exc, context=self._context)



            elif result is None:

                # Bare yield relinquishes control for one event loop iteration.

                self._loop.call_soon(self.__step, context=self._context)

            elif inspect.isgenerator(result):

                # Yielding a generator is just wrong.

                new_exc = RuntimeError(

                    f'yield was used instead of yield from for '

                    f'generator in task {self!r} with {result!r}')

                self._loop.call_soon(

                    self.__step, new_exc, context=self._context)

            else:

                # Yielding something else is an error.

                new_exc = RuntimeError(f'Task got bad yield: {result!r}')

                self._loop.call_soon(

                    self.__step, new_exc, context=self._context)

        finally:

            _leave_task(self._loop, self)

            self = None  # Needed to break cycles when an exception occurs.



    def __wakeup(self, future):

        try:

            future.result()

        except BaseException as exc:

            # This may also be a cancellation.

            self.__step(exc)

        else:

            # Don't pass the value of `future.result()` explicitly,

            # as `Future.__iter__` and `Future.__await__` don't need it.

            # If we call `_step(value, None)` instead of `_step()`,

            # Python eval loop would use `.send(value)` method call,

            # instead of `__next__()`, which is slower for futures

            # that return non-generator iterators from their `__iter__`.

            self.__step()

        self = None  # Needed to break cycles when an exception occurs.





_PyTask = Task





try:

    import _asyncio

except ImportError:

    pass

else:

    # _CTask is needed for tests.

    Task = _CTask = _asyncio.Task





def create_task(coro, *, name=None):

    """Schedule the execution of a coroutine object in a spawn task.



    Return a Task object.

    """

    loop = events.get_running_loop()

    task = loop.create_task(coro)

    _set_task_name(task, name)

    return task





# wait() and as_completed() similar to those in PEP 3148.



FIRST_COMPLETED = concurrent.futures.FIRST_COMPLETED

FIRST_EXCEPTION = concurrent.futures.FIRST_EXCEPTION

ALL_COMPLETED = concurrent.futures.ALL_COMPLETED





async def wait(fs, *, loop=None, timeout=None, return_when=ALL_COMPLETED):

    """Wait for the Futures and coroutines given by fs to complete.



    The sequence futures must not be empty.



    Coroutines will be wrapped in Tasks.



    Returns two sets of Future: (done, pending).



    Usage:



        done, pending = await asyncio.wait(fs)



    Note: This does not raise TimeoutError! Futures that aren't done

    when the timeout occurs are returned in the second set.

    """

    if futures.isfuture(fs) or coroutines.iscoroutine(fs):

        raise TypeError(f"expect a list of futures, not {type(fs).__name__}")

    if not fs:

        raise ValueError('Set of coroutines/Futures is empty.')

    if return_when not in (FIRST_COMPLETED, FIRST_EXCEPTION, ALL_COMPLETED):

        raise ValueError(f'Invalid return_when value: {return_when}')



    if loop is None:

        loop = events.get_running_loop()

    else:

        warnings.warn("The loop argument is deprecated since Python 3.8, "

                      "and scheduled for removal in Python 3.10.",

                      DeprecationWarning, stacklevel=2)



    fs = {ensure_future(f, loop=loop) for f in set(fs)}



    return await _wait(fs, timeout, return_when, loop)





def _release_waiter(waiter, *args):

    if not waiter.done():

        waiter.set_result(None)





async def wait_for(fut, timeout, *, loop=None):

    """Wait for the single Future or coroutine to complete, with timeout.



    Coroutine will be wrapped in Task.



    Returns result of the Future or coroutine.  When a timeout occurs,

    it cancels the task and raises TimeoutError.  To avoid the task

    cancellation, wrap it in shield().



    If the wait is cancelled, the task is also cancelled.



    This function is a coroutine.

    """

    if loop is None:

        loop = events.get_running_loop()

    else:

        warnings.warn("The loop argument is deprecated since Python 3.8, "

                      "and scheduled for removal in Python 3.10.",

                      DeprecationWarning, stacklevel=2)



    if timeout is None:

        return await fut



    if timeout <= 0:

        fut = ensure_future(fut, loop=loop)



        if fut.done():

            return fut.result()



        fut.cancel()

        raise exceptions.TimeoutError()



    waiter = loop.create_future()

    timeout_handle = loop.call_later(timeout, _release_waiter, waiter)

    cb = functools.partial(_release_waiter, waiter)



    fut = ensure_future(fut, loop=loop)

    fut.add_done_callback(cb)



    try:

        # wait until the future completes or the timeout

        try:

            await waiter

        except exceptions.CancelledError:

            fut.remove_done_callback(cb)

            fut.cancel()

            raise



        if fut.done():

            return fut.result()

        else:

            fut.remove_done_callback(cb)

            # We must ensure that the task is not running

            # after wait_for() returns.

            # See https://bugs.python.org/issue32751

            await _cancel_and_wait(fut, loop=loop)

            raise exceptions.TimeoutError()

    finally:

        timeout_handle.cancel()





async def _wait(fs, timeout, return_when, loop):

    """Internal helper for wait().



    The fs argument must be a collection of Futures.

    """

    assert fs, 'Set of Futures is empty.'

    waiter = loop.create_future()

    timeout_handle = None

    if timeout is not None:

        timeout_handle = loop.call_later(timeout, _release_waiter, waiter)

    counter = len(fs)



    def _on_completion(f):

        nonlocal counter

        counter -= 1

        if (counter <= 0 or

            return_when == FIRST_COMPLETED or

            return_when == FIRST_EXCEPTION and (not f.cancelled() and

                                                f.exception() is not None)):

            if timeout_handle is not None:

                timeout_handle.cancel()

            if not waiter.done():

                waiter.set_result(None)



    for f in fs:

        f.add_done_callback(_on_completion)



    try:

        await waiter

    finally:

        if timeout_handle is not None:

            timeout_handle.cancel()

        for f in fs:

            f.remove_done_callback(_on_completion)



    done, pending = set(), set()

    for f in fs:

        if f.done():

            done.add(f)

        else:

            pending.add(f)

    return done, pending





async def _cancel_and_wait(fut, loop):

    """Cancel the *fut* future or task and wait until it completes."""



    waiter = loop.create_future()

    cb = functools.partial(_release_waiter, waiter)

    fut.add_done_callback(cb)



    try:

        fut.cancel()

        # We cannot wait on *fut* directly to make

        # sure _cancel_and_wait itself is reliably cancellable.

        await waiter

    finally:

        fut.remove_done_callback(cb)





# This is *not* a @coroutine!  It is just an iterator (yielding Futures).

def as_completed(fs, *, loop=None, timeout=None):

    """Return an iterator whose values are coroutines.



    When waiting for the yielded coroutines you'll get the results (or

    exceptions!) of the original Futures (or coroutines), in the order

    in which and as soon as they complete.



    This differs from PEP 3148; the proper way to use this is:



        for f in as_completed(fs):

            result = await f  # The 'await' may raise.

            # Use result.



    If a timeout is specified, the 'await' will raise

    TimeoutError when the timeout occurs before all Futures are done.



    Note: The futures 'f' are not necessarily members of fs.

    """

    if futures.isfuture(fs) or coroutines.iscoroutine(fs):

        raise TypeError(f"expect a list of futures, not {type(fs).__name__}")



    from .queues import Queue  # Import here to avoid circular import problem.

    done = Queue(loop=loop)



    if loop is None:

        loop = events.get_event_loop()

    else:

        warnings.warn("The loop argument is deprecated since Python 3.8, "

                      "and scheduled for removal in Python 3.10.",

                      DeprecationWarning, stacklevel=2)

    todo = {ensure_future(f, loop=loop) for f in set(fs)}

    timeout_handle = None



    def _on_timeout():

        for f in todo:

            f.remove_done_callback(_on_completion)

            done.put_nowait(None)  # Queue a dummy value for _wait_for_one().

        todo.clear()  # Can't do todo.remove(f) in the loop.



    def _on_completion(f):

        if not todo:

            return  # _on_timeout() was here first.

        todo.remove(f)

        done.put_nowait(f)

        if not todo and timeout_handle is not None:

            timeout_handle.cancel()



    async def _wait_for_one():

        f = await done.get()

        if f is None:

            # Dummy value from _on_timeout().

            raise exceptions.TimeoutError

        return f.result()  # May raise f.exception().



    for f in todo:

        f.add_done_callback(_on_completion)

    if todo and timeout is not None:

        timeout_handle = loop.call_later(timeout, _on_timeout)

    for _ in range(len(todo)):

        yield _wait_for_one()





@types.coroutine

def __sleep0():

    """Skip one event loop run cycle.



    This is a private helper for 'asyncio.sleep()', used

    when the 'delay' is set to 0.  It uses a bare 'yield'

    expression (which Task.__step knows how to handle)

    instead of creating a Future object.

    """

    yield





async def sleep(delay, result=None, *, loop=None):

    """Coroutine that completes after a given time (in seconds)."""

    if delay <= 0:

        await __sleep0()

        return result



    if loop is None:

        loop = events.get_running_loop()

    else:

        warnings.warn("The loop argument is deprecated since Python 3.8, "

                      "and scheduled for removal in Python 3.10.",

                      DeprecationWarning, stacklevel=2)



    future = loop.create_future()

    h = loop.call_later(delay,

                        futures._set_result_unless_cancelled,

                        future, result)

    try:

        return await future

    finally:

        h.cancel()





def ensure_future(coro_or_future, *, loop=None):

    """Wrap a coroutine or an awaitable in a future.



    If the argument is a Future, it is returned directly.

    """

    if coroutines.iscoroutine(coro_or_future):

        if loop is None:

            loop = events.get_event_loop()

        task = loop.create_task(coro_or_future)

        if task._source_traceback:

            del task._source_traceback[-1]

        return task

    elif futures.isfuture(coro_or_future):

        if loop is not None and loop is not futures._get_loop(coro_or_future):

            raise ValueError('The future belongs to a different loop than '

                             'the one specified as the loop argument')

        return coro_or_future

    elif inspect.isawaitable(coro_or_future):

        return ensure_future(_wrap_awaitable(coro_or_future), loop=loop)

    else:

        raise TypeError('An asyncio.Future, a coroutine or an awaitable is '

                        'required')





@types.coroutine

def _wrap_awaitable(awaitable):

    """Helper for asyncio.ensure_future().



    Wraps awaitable (an object with __await__) into a coroutine

    that will later be wrapped in a Task by ensure_future().

    """

    return (yield from awaitable.__await__())



_wrap_awaitable._is_coroutine = _is_coroutine





class _GatheringFuture(futures.Future):

    """Helper for gather().



    This overrides cancel() to cancel all the children and act more

    like Task.cancel(), which doesn't immediately mark itself as

    cancelled.

    """



    def __init__(self, children, *, loop=None):

        super().__init__(loop=loop)

        self._children = children

        self._cancel_requested = False



    def cancel(self):

        if self.done():

            return False

        ret = False

        for child in self._children:

            if child.cancel():

                ret = True

        if ret:

            # If any child tasks were actually cancelled, we should

            # propagate the cancellation request regardless of

            # *return_exceptions* argument.  See issue 32684.

            self._cancel_requested = True

        return ret





def gather(*coros_or_futures, loop=None, return_exceptions=False):

    """Return a future aggregating results from the given coroutines/futures.



    Coroutines will be wrapped in a future and scheduled in the event

    loop. They will not necessarily be scheduled in the same order as

    passed in.



    All futures must share the same event loop.  If all the tasks are

    done successfully, the returned future's result is the list of

    results (in the order of the original sequence, not necessarily

    the order of results arrival).  If *return_exceptions* is True,

    exceptions in the tasks are treated the same as successful

    results, and gathered in the result list; otherwise, the first

    raised exception will be immediately propagated to the returned

    future.



    Cancellation: if the outer Future is cancelled, all children (that

    have not completed yet) are also cancelled.  If any child is

    cancelled, this is treated as if it raised CancelledError --

    the outer Future is *not* cancelled in this case.  (This is to

    prevent the cancellation of one child to cause other children to

    be cancelled.)

    """

    if not coros_or_futures:

        if loop is None:

            loop = events.get_event_loop()

        else:

            warnings.warn("The loop argument is deprecated since Python 3.8, "

                          "and scheduled for removal in Python 3.10.",

                          DeprecationWarning, stacklevel=2)

        outer = loop.create_future()

        outer.set_result([])

        return outer



    def _done_callback(fut):

        nonlocal nfinished

        nfinished += 1



        if outer.done():

            if not fut.cancelled():

                # Mark exception retrieved.

                fut.exception()

            return



        if not return_exceptions:

            if fut.cancelled():

                # Check if 'fut' is cancelled first, as

                # 'fut.exception()' will *raise* a CancelledError

                # instead of returning it.

                exc = exceptions.CancelledError()

                outer.set_exception(exc)

                return

            else:

                exc = fut.exception()

                if exc is not None:

                    outer.set_exception(exc)

                    return



        if nfinished == nfuts:

            # All futures are done; create a list of results

            # and set it to the 'outer' future.

            results = []



            for fut in children:

                if fut.cancelled():

                    # Check if 'fut' is cancelled first, as

                    # 'fut.exception()' will *raise* a CancelledError

                    # instead of returning it.

                    res = exceptions.CancelledError()

                else:

                    res = fut.exception()

                    if res is None:

                        res = fut.result()

                results.append(res)



            if outer._cancel_requested:

                # If gather is being cancelled we must propagate the

                # cancellation regardless of *return_exceptions* argument.

                # See issue 32684.

                outer.set_exception(exceptions.CancelledError())

            else:

                outer.set_result(results)



    arg_to_fut = {}

    children = []

    nfuts = 0

    nfinished = 0

    for arg in coros_or_futures:

        if arg not in arg_to_fut:

            fut = ensure_future(arg, loop=loop)

            if loop is None:

                loop = futures._get_loop(fut)

            if fut is not arg:

                # 'arg' was not a Future, therefore, 'fut' is a new

                # Future created specifically for 'arg'.  Since the caller

                # can't control it, disable the "destroy pending task"

                # warning.

                fut._log_destroy_pending = False



            nfuts += 1

            arg_to_fut[arg] = fut

            fut.add_done_callback(_done_callback)



        else:

            # There's a duplicate Future object in coros_or_futures.

            fut = arg_to_fut[arg]



        children.append(fut)



    outer = _GatheringFuture(children, loop=loop)

    return outer





def shield(arg, *, loop=None):

    """Wait for a future, shielding it from cancellation.



    The statement



        res = await shield(something())



    is exactly equivalent to the statement



        res = await something()



    *except* that if the coroutine containing it is cancelled, the

    task running in something() is not cancelled.  From the POV of

    something(), the cancellation did not happen.  But its caller is

    still cancelled, so the yield-from expression still raises

    CancelledError.  Note: If something() is cancelled by other means

    this will still cancel shield().



    If you want to completely ignore cancellation (not recommended)

    you can combine shield() with a try/except clause, as follows:



        try:

            res = await shield(something())

        except CancelledError:

            res = None

    """

    if loop is not None:

        warnings.warn("The loop argument is deprecated since Python 3.8, "

                      "and scheduled for removal in Python 3.10.",

                      DeprecationWarning, stacklevel=2)

    inner = ensure_future(arg, loop=loop)

    if inner.done():

        # Shortcut.

        return inner

    loop = futures._get_loop(inner)

    outer = loop.create_future()



    def _inner_done_callback(inner):

        if outer.cancelled():

            if not inner.cancelled():

                # Mark inner's result as retrieved.

                inner.exception()

            return



        if inner.cancelled():

            outer.cancel()

        else:

            exc = inner.exception()

            if exc is not None:

                outer.set_exception(exc)

            else:

                outer.set_result(inner.result())





    def _outer_done_callback(outer):

        if not inner.done():

            inner.remove_done_callback(_inner_done_callback)



    inner.add_done_callback(_inner_done_callback)

    outer.add_done_callback(_outer_done_callback)

    return outer





def run_coroutine_threadsafe(coro, loop):

    """Submit a coroutine object to a given event loop.



    Return a concurrent.futures.Future to access the result.

    """

    if not coroutines.iscoroutine(coro):

        raise TypeError('A coroutine object is required')

    future = concurrent.futures.Future()



    def callback():

        try:

            futures._chain_future(ensure_future(coro, loop=loop), future)

        except (SystemExit, KeyboardInterrupt):

            raise

        except BaseException as exc:

            if future.set_running_or_notify_cancel():

                future.set_exception(exc)

            raise



    loop.call_soon_threadsafe(callback)

    return future





# WeakSet containing all alive tasks.

_all_tasks = weakref.WeakSet()



# Dictionary containing tasks that are currently active in

# all running event loops.  {EventLoop: Task}

_current_tasks = {}





def _register_task(task):

    """Register a new task in asyncio as executed by loop."""

    _all_tasks.add(task)





def _enter_task(loop, task):

    current_task = _current_tasks.get(loop)

    if current_task is not None:

        raise RuntimeError(f"Cannot enter into task {task!r} while another "

                           f"task {current_task!r} is being executed.")

    _current_tasks[loop] = task





def _leave_task(loop, task):

    current_task = _current_tasks.get(loop)

    if current_task is not task:

        raise RuntimeError(f"Leaving task {task!r} does not match "

                           f"the current task {current_task!r}.")

    del _current_tasks[loop]





def _unregister_task(task):

    """Unregister a task."""

    _all_tasks.discard(task)





_py_register_task = _register_task

_py_unregister_task = _unregister_task

_py_enter_task = _enter_task

_py_leave_task = _leave_task





try:

    from _asyncio import (_register_task, _unregister_task,

                          _enter_task, _leave_task,

                          _all_tasks, _current_tasks)

except ImportError:

    pass

else:

    _c_register_task = _register_task

    _c_unregister_task = _unregister_task

    _c_enter_task = _enter_task

    _c_leave_task = _leave_task