Asyncio is blocking using FastAPI [duplicate]

Question

I have a function that make a post request with a lot of treatment. All of that takes 30 seconds.

I need to execute this function every 6 mins. So I used asyncio for that ... But it's not asynchrone my api is blocked since the end of function ... Later I will have treatment that takes 5 minutes to execute.

def update_all():
    # do request and treatment (30 secs)

async run_update_all():
    while True:
        await asyncio.sleep(6 * 60)
        update_all()

loop = asyncio.get_event_loop()
loop.create_task(run_update_all())

So, I don't understand why during the execute time of update_all() all requests comming are in pending, waiting for the end of update_all() instead of being asynchronous

If update_all() is not an async function it will block the thread. It's not clear why you are expecting it not to. — Mark
– Mark, Commented Oct 20, 2022 at 17:23
Because I think there is a way to use a blocking function in a thread ? But I don't know how to do that — LelouchXV
– LelouchXV, Commented Oct 20, 2022 at 17:56
You may be looking for the run_in_executor method, which will wrap a synchronous function in a thread (or process) so that it doesn't block your event loop. — larsks
– larsks, Commented Oct 20, 2022 at 18:04
Does this answer your question? asyncio, wrapping a normal function as asynchronous — SuperStormer
– SuperStormer, Commented Oct 20, 2022 at 18:19

LelouchXV · Accepted Answer · 2022-10-20 19:15:12Z

4

I found an answer with the indication of larsks

I did that :

def update_all():
    # Do synchrone post request and treatment that take long time

async def launch_async():
    loop = asyncio.get_event_loop()
    while True:
        await asyncio.sleep(120)
        loop.run_in_executore(None, update_all)

asyncio.create_task(launch_async())

With that code I'm able to launch a synchrone function every X seconds without blocking the main thread of FastApi :D

I hope that will help other people in the same case than me.

answered Oct 20, 2022 at 19:15

LelouchXV

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1 Comment

clesiemo3 Over a year ago

Thanks this helped me get around the blocking behavior I was stuck on trying to get an "after startup" event to fire (basically launch this async task in startup event function with a timer)

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