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devel / comp.lang.python / Re: Using a background thread with asyncio/futures with flask

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o Re: Using a background thread with asyncio/futures with flaskFrank Millman

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Re: Using a background thread with asyncio/futures with flask

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From: frank@chagford.com (Frank Millman)
Newsgroups: comp.lang.python
Subject: Re: Using a background thread with asyncio/futures with flask
Date: Fri, 22 Mar 2024 13:23:43 +0200
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<7af73918-8209-4393-8aa2-140940567456@chagford.com>
 by: Frank Millman - Fri, 22 Mar 2024 11:23 UTC

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())

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