[ruby-core:108518] [Ruby master Feature#18774] Add Queue#pop(timeout:)

Issue #18774 has been updated by Eregon (Benoit Daloze).


Indeed, I forgot to mention that. I think returning `nil` is easiest, most consistent and convenient.
I believe it is already common practice to use another element than `nil` in a Queue for special markers, so it seems a rare issue in practice.

> however pop already returns nil when called in "non_block" mode

Actually it's `queue empty (ThreadError)` in that case. Which seems pretty expensive for such a poll case, but that's the current semantics.
When the queue is closed, then `queue.pop` returns `nil` indeed.

FWIW the semantics of Rubinius' `Channel#receive_timeout` is to return `nil` when timed out:
https://github.com/rubinius/rubinius/blob/b7a755c83f3dd3f0c1f5e546f0e58fb61851ea44/machine/class/channel.cpp#L96

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Feature #18774: Add Queue#pop(timeout:)
https://bugs.ruby-lang.org/issues/18774#change-97559

* Author: Eregon (Benoit Daloze)
* Status: Open
* Priority: Normal
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This has been mentioned many times but somehow was never added.
It is useful for many different use cases:
* Implementing Timeout#timeout without needing to create a Thread per call which is very inefficient (especially when the timeout is not hit): https://github.com/ruby/timeout/pull/14#issuecomment-1123380880
* @jeremyevans0 I would love a Queue#pop :timeout argument. It would simplify the mutex/condition variable approach currently used for Sequel's connection pool.
* @byroot Same. I wanted it so many times
* https://bugs.ruby-lang.org/issues/17363
* https://spin.atomicobject.com/2014/07/07/ruby-queue-pop-timeout/ + https://spin.atomicobject.com/2017/06/28/queue-pop-with-timeout-fixed/
* More in my email searches but this seems already plenty

I think it should be a keyword argument for clarity, and so there is no confusion with the existing optional argument `non_block=false`.



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