Redundant self.empty() check in asyncio.Queue.get()

[deadlovelll]

Bug report

Bug description:

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

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-149740: Remove redundant self.empty() check in asyncio.Queue.get() #149741

[picnixz]

The docs say:

Raises QueueShutDown if the queue has been shut down and is empty, or if the queue has been shut down immediately.

So I don't think it's redundant. We may have a race if the queue is empty after the shutdown check.

cc @kumaraditya303

[jonathandung]

asyncio.Queue should only be used in a single thread, so I don't see why there would be a race.

[picnixz]

OTOH one could argue that we still want to raise the shutdown even if the queue is not empty. After looking at other parts of the code it looks like the pattern assumes that shutdown implies no more queued callbacks.