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def run_once():
    """
    A helper that takes one trip through the event-loop to process any
    pending Futures. This is a no-op for Twisted, because you don't
    need to use the event-loop to get callbacks to happen in Twisted.
    """

    import txaio

    if txaio.using_twisted:
        return

    try:
        import sys
        import asyncio

        if sys.version_info >= (3, 7):
            # https://github.com/crossbario/txaio/issues/139
            def _run_once(loop):
                """Legacy API to run once through the event loop.

                This is the recommended pattern for test code.  It will poll the
                selector once and run all callbacks scheduled in response to I/O
                events.
                """
                loop.call_soon(loop.stop)
                loop.run_forever()

        else:
            from asyncio.test_utils import run_once as _run_once

        return _run_once(txaio.config.loop or _get_loop())

    except ImportError:
        import trollius as asyncio

        # let any trollius import error out; if we're not using
        # twisted, and have no asyncio *and* no trollius, that's a
        # problem.

        # copied from asyncio.testutils because trollius has no
        # testutils"

        # just like modern asyncio.testutils.run_once does it...
        loop = asyncio.get_event_loop()
        loop.stop()
        loop.run_forever()
        asyncio.gather(*asyncio.Task.all_tasks())


def _get_loop():
    import asyncio

    try:
        return asyncio.get_event_loop()
    except RuntimeError:
        loop = asyncio.new_event_loop()
        asyncio.set_event_loop(loop)
        return loop


def _await(future):
    """
    Essentially just a way to call "run_until_complete" that becomes a
    no-op if we're using Twisted.
    """

    import txaio

    if txaio.using_twisted:
        return

    try:
        import asyncio
    except ImportError:
        import trollius as asyncio

    asyncio.get_event_loop().run_until_complete(future)
