gh-149740: Remove redundant self.empty() check in asyncio.Queue.get()

[deadlovelll]

Bug description:

In Lib/asyncio/queues.py, Queue.get() contains a redundant call to self.empty() inside its waiting loop:

async def get(self):
    while self.empty():
        if self._is_shutdown and self.empty():   # second self.empty() is redundant
            raise QueueShutDown

self.empty() is guaranteed to be true by the enclosing while self.empty() the loop body cannot execute otherwise. This check is a dead code.

Proposed fix:

Drop the redundant and self.empty():

while self.empty():
    if self._is_shutdown:
        raise QueueShutDown

This PR is cleanup only, no behavior change

• Issue: Redundant self.empty() check in asyncio.Queue.get() #149740

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[picnixz]

I don't think it's correct. See the issue.

[picnixz]

Looking at the other parts of the code, I think it would make indeed more sense to consistently raise on shutdown whether the queue is empty or not. So it is not dead code but it rathet looks like a bug to me.

[MojoVampire]

You could just change the loop to while self.empty() and not self._is_shutdown:; get_nowait already rechecks all this stuff when it's called, and would raise the necessary exception for us.

[picnixz]

I would prefer keeping this as is, so to keep the symmetry in the get() method.

[deadlovelll]

Looking at the other parts of the code, I think it would make indeed more sense to consistently raise on shutdown whether the queue is empty or not. So it is not dead code but it rathet looks like a bug to me.

Hello! Sorry for the slow follow-up, just lost the conversation.

Its not a bug because get() only raises QueueShutDown if its empty and shutdown, OR queue was shutdown immediatly (link). shutdown(immedeate=True) is not separate path, it sets the self._is_shutdown to True, then clears the queue. get() sees an empty queue and shutdown flag and raises QueueShutDown (link)

You also mentioned in issue body that there can be race, but all asyncio primitives are not thread-safe (link)

So there's no behavioral bug here, just drops the duplicate check

We'll be happy to close it if you prefer to leave it as is