[ruby-core:109786] [Ruby master Feature#18982] Add an `exception: false` argument for Queue#push, Queue#pop, SizedQueue#push and SizedQueue#pop

Issue #18982 has been updated by shyouhei (Shyouhei Urabe).


I don't think people want to exit from a `while item = queue.pop` loop because the queue would block.  `for (;;) { if (errno != EAGAIN) break; ... }` is a C idiom (people often break from a loop on error, _except_ EAGAIN).

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Feature #18982: Add an `exception: false` argument for Queue#push, Queue#pop, SizedQueue#push and SizedQueue#pop
https://bugs.ruby-lang.org/issues/18982#change-99022

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
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This replaces [Feature #18965]

Currently these methods raise in three occasions:

  - `ThreadError(queue empty)` for `#pop` in `nonblock=true` mode, and the operation would block.
  - `ThreadError(queue full)` for `SizedQueue#push` in `nonblock=true` mode, and the operation would block.
  - `ClosedQueueError` if trying to `#push` in a closed queue.

I see several reasons to prefer a `nil` return value.

- Queue is often used in conjunction with threads, so you have to be very careful not to rescue an unrelated `ThreadError`.
- Queue if often used for low level code, deep in the stack, so exceptions are costly.

I propose that passing `exception: false` would cause the method to return `nil` instead of raising in the three cases listed above.

The argument `exception: true` is consistent with various other methods such as `IO#read_nonblock(exception: false)`.



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