Internally, is asyncio run_forever() basically a while True loop?

Question

python asyncio run_forever or while True is similar but it is a "should I do this..." question.

I am more trying to understand if the internals of python asyncio is basically a

while True:
  ...
  time.sleep(1)

(or more precisely... while not stopped: loop.

Does it use also use sleep to prevent spin waits?

Vouge

Does stackoverflow.com/questions/40851872 help? – Muffler

Answer 1

Check the source code? If you're in IPython, it's pretty trivial:

>>> import asyncio
>>> loop = asyncio.get_event_loop()
>>> loop.run_forever??

The core of the loop (on my 3.11 install) is:

            while True:
                self._run_once()
                if self._stopping:
                    break

So yep, it's a while True: loop. You can check loop._run_once?? to see the source code for that, and it's much more complicated, but short version is that it's not a sleep, it's a select call that blocks (not polls) until some async task completes, adds itself to the queue, and signals the event loop that there is work to do.

Fp

I think that key thing is the select I presume that would be significantly better than a sleep I presume it's waiting for an OS event and constant rechecking. Can you add that to your answer if it is true. – Vouge

@ArchimedesTrajano: That's already in the answer? select is signaled, it blocks without consuming resources until that happens. – Fp

Yup but the part that says "without consuming any resources" is the key phrase that should be added to the answer. I wasn't sure about it until your comment. – Vouge