Submit Tornado Coroutine to IOLoop.current().

    :param fn: Tornado Coroutine to execute
    :param io_loop: Tornado IOLoop where to schedule the coroutine
    :param args: Args to pass to coroutine
    :param kwargs: Kwargs to pass to coroutine
    :returns tornado.concurrent.Future: future result of coroutine

def submit(fn, io_loop, *args, **kwargs):
    """Submit Tornado Coroutine to IOLoop.current().

    :param fn: Tornado Coroutine to execute
    :param io_loop: Tornado IOLoop where to schedule the coroutine
    :param args: Args to pass to coroutine
    :param kwargs: Kwargs to pass to coroutine
    :returns tornado.concurrent.Future: future result of coroutine
    """
    future = Future()

    def execute():
        """Execute fn on the IOLoop."""
        try:
            result = gen.maybe_future(fn(*args, **kwargs))
        except Exception:
            # The function we ran didn't return a future and instead raised
            # an exception. Let's pretend that it returned this dummy
            # future with our stack trace.
            f = gen.Future()
            f.set_exc_info(sys.exc_info())
            on_done(f)
        else:
            result.add_done_callback(on_done)

    def on_done(tornado_future):
        """
        Set tornado.Future results to the concurrent.Future.
        :param tornado_future:
        """
        exception = tornado_future.exception()
        if not exception:
            future.set_result(tornado_future.result())
        else:
            future.set_exception(exception)

    io_loop.add_callback(execute)

    return future