asyncio: 50ms delay between put_nowait and get to/from a queue

Question

I have a python asyncio application, with several coroutines being run within a single thread. Some data is being passed using queues.

The queue consumer looks like this:

    async def queue_consumer(q):
        """Consume from an asyncio.Queue, making it an async iterable"""
        while True:
            try:
                e = await q.get()
                yield e
            except:
                continue

the consumer is being pulled from with async for. In this particular case the coroutine which consumes from a specific queue sequentially calls some code which puts data into its queue with put_nowait. EDIT: In this particular case coroutine A, which is listening for inbound network traffic, puts message into queue of coroutine B.

I have noticed that there is a consistent ~50ms delay between a call to put_nowait in coroutine A and then the data being processed as a result of pulling it from queue async iterable in coroutine B.

I suspect it might have something to do with some asyncio internal polling resolution, but I am not sure, not I would suspect where such configuration could be modified.

I would be very much interested in increasing event polling frequency in the asyncio loop, hence, decreasing observed delay between put_nowait and get to/from a queue between coroutines. Maybe also there's a way to hint asyncio framework to process items from the queue earlier?

NB: the application I am working with is not doing any computationally demanding work.

Answer 1

It turns out the problem was caused by my app doing some UI updates with prompt_toolkit. I tracked this down by placing some measurements within _run_once. Anyway, the queue was not being processed because the event loop was busy executing some UI code that I did not expect to take so much time.