Avoid busy loop in workers, while waiting for work.

[briot]

My application has a main loop that basically looks like

    async with aiomultiprocess.Pool(
        processes=Global.PROCESSES,
        initializer=Global.create,
        initargs=(args, Global.psql, openai_factory),
        maxtasksperchild=0,   # kill processes after those tasks
        childconcurrency=Global.CHILD_CONCURRENCY,
        queuecount=Global.QUEUES,
        scheduler=scheduler,
        loop_initializer=uvloop.new_event_loop,
    ) as pool:
        monitor = Monitor(pool, scheduler=scheduler, job_factory=job_factory)

        async with asyncio.TaskGroup() as tg:
            _ = tg.create_task(monitor.listen()

The last part is listening for postgresql notifications when database tables change, and then calling queue_work(). One minor issue is that the worker processes are in fact doing busy looping (with a small 0.005s delay) while calling get_no_wait on the queue repeatedly. On the other hand, if the worker is not handling any pending work, we might as well call a blocking get while waiting for initial work.