Python-asyncio - using timers/threading to terminate async

Question

I have an async coroutine that I want to terminate using a timer/thread. The coroutine is based of this example from aiortc.

args = parse_args()
client = Client(connection, media, args.role)

# run event loop
loop = asyncio.get_event_loop()

try:
    timer = None
    if args.timeout:
        print("Timer started")
        timer = threading.Timer(args.timeout, loop.run_until_complete, args=(client.close(),))
        timer.start()

    loop.run_until_complete(client.run())

    if timer:
        timer.join()
except KeyboardInterrupt:
    pass
finally:
    # cleanup
    loop.run_until_complete(client.close())

This does not work and raises RuntimeError('This event loop is already running')

Why does this raise the error? My guess is that it's because the loop is running on a different thread. However, creating a new loop doesn't work as it gets a future attached to a different loop.

def timer_callback():
    new_loop = asyncio.new_event_loop()
    new_loop.run_until_complete(client.close())

Following that, how can I use a timer to end the script?

user4815162342 · Accepted Answer · 2022-01-12 11:07:33Z

2

Following that, how can I use a timer to end the script?

You can call asyncio.run_coroutine_threadsafe() to submit a coroutine to an event loop running in another thread:

    if args.timeout:
        print("Timer started")
        timer = threading.Timer(
            args.timeout,
            asyncio.run_coroutine_threadsafe,
            args=(client.close(), loop),
        )
        timer.start()

Note, however, that since you're working with asyncio, you don't need a dedicated thread for the timer, you could just create a coroutine and tell it to wait before doing something:

    if args.timeout:
        print("Timer started")
        async def close_after_timeout(): 
            await asyncio.sleep(args.timeout)
            await client.close()
        loop.create_task(close_after_timeout())

edited Jan 12, 2022 at 11:07

answered Jan 12, 2022 at 9:33

user4815162342

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Comments

Jordan Sim · Accepted Answer · 2022-01-12 00:48:25Z

0

This isn't the general solution that I was looking for, I added a timeout variable to the client constructor, and within client.run() I added asyncio.sleep(timeout) which would exit the loop. This is enough for my purposes.

answered Jan 12, 2022 at 0:48

Jordan Sim

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