Using a background thread with asyncio/futures with flask

[Frank Millman]

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())