Using a background thread with asyncio/futures with flask
Frank Millman
frank at chagford.com
Fri Mar 22 07:28:56 EDT 2024
On 2024-03-22 1:23 PM, Frank Millman via Python-list wrote:
> On 2024-03-22 12:09 PM, Frank Millman via Python-list wrote:
>>
>> I am no expert. However, I do have something similar in my app, and it
>> works.
>>
>> I do not use 'await future', I use 'asyncio.wait_for(future)'.
>>
>
> I tested it and it did not work.
>
> I am not sure, but I think the problem is that you have a mixture of
> blocking and non-blocking functions.
>
> Here is a version that works. However, it is a bit different, so I don't
> know if it fits your use case.
>
> I have replaced the threads with background asyncio tasks.
>
> I have replaced instances of queue.Queue with asyncio.Queue.
>
> Frank
>
> ===============================================
>
> import asyncio
>
> in_queue = asyncio.Queue()
> out_queue = asyncio.Queue()
>
> async def worker():
> print("worker started running")
> while True:
> future = await in_queue.get()
> print(f"worker got future: {future}")
> await asyncio.sleep(5)
> print("worker sleeped")
> await out_queue.put(future)
>
> async def finalizer():
> print("finalizer started running")
> while True:
> future = await out_queue.get()
> print(f"finalizer got future: {future}")
> future.set_result("completed")
> print("finalizer set result")
>
> async def main():
> asyncio.create_task(worker()) # start a background task
> asyncio.create_task(finalizer()) # ditto
> future = asyncio.get_event_loop().create_future()
> await in_queue.put(future)
> print(f"main put future: {future}")
> result = await asyncio.wait_for(future, timeout=None)
> print(result)
>
> if __name__ == "__main__":
> # loop = asyncio.get_event_loop()
> # loop.run_until_complete(main())
>
> # this is the preferred way to start an asyncio app
> asyncio.run(main())
>
>
One more point.
If I change 'await asyncio.wait_for(future, timeout=None)' back to your
original 'await future', it still works.
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