def _send_coroutine():
    """
    Creates a running coroutine to receive message instances and send
    them in a futures executor.
    """
    with PoolExecutor() as executor:
        while True:
            msg = yield
            future = executor.submit(msg.send)
            future.add_done_callback(_exception_handler)
Creates a running coroutine to receive message instances and send
    them in a futures executor.