Function _wait

Lib/asyncio/tasks.py:490–534

Internal helper for wait(). The fs argument must be a collection of Futures.

(fs, timeout, return_when, loop)

        return await fut

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)
    cur_task = current_task()

    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)
        futures.future_discard_from_awaited_by(f, cur_task)

    for f in fs:
        f.add_done_callback(_on_completion)
        futures.future_add_to_awaited_by(f, cur_task)

    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):