Python - asyncio - Wait for a future inside a callback

Question

Here is my code, I want my_reader to wait maximum 5 seconds for a future then do something with the my_future.result() . Please note that my_reader is not a coroutine , it is a callback .

import asyncio, socket

sock = ...

async def my_coroutine():
    ...

def my_reader():
    my_future = asyncio.Future()
    ...

    # I want to wait (with a timeout) for my_future


loop = asyncio.get_event_loop()
loop.add_reader(sock, my_reader)
loop.run_forever()
loop.close()

I don't want to use either:

• AbstractEventLoop.create_datagram_endpoint()
• AbstractEventLoop.create_connection()
• ...

The socket I have is returned from another module and I have to read packets with a given size. The transfer must happen under 5 seconds.

How to wait for a future inside a callback?

Answer 1

Sorry, waiting in callbacks is impossible. Callback should be executed instantly by definition -- otherwise event loop hangs on callback execution period.

Your logic should be built on coroutines but low-level on_read callback may inform these coroutines by setting a value of future.

See aiopg.connection for inspiration. The callback is named Connection._ready .

Answer 2

You should run the coroutine separately and send data to it from the callback via Queue.

Look on this answer:

https://stackoverflow.com/a/29475218/1112457