Issue #10600 has been updated by Koichi Sasada.


I decide to reduce specification of Queue#close. For closed queues, deq returns nil.

No exception is raised for deq.
Other tokens are also not supported.

We can introduce them as new feature.

For Ruby 2.3 (or just now), Queue#close is only for shortcut of such common case.

```ruby
consumer_threads = (1..3).map{
  Thread.new do
    while e = q.pop
      do_something e
    end
  end
}

q.push 1
q.push 2
3.times{
  q.push nil # terminater
}
```

We can write last 3 lines with:

```ruby
q.close
```

I agree that it is reasonable to add options (raise exception, and so on) to Queue.new.
We can add this feature later.


----------------------------------------
Feature #10600: [PATCH] Queue#close
https://bugs.ruby-lang.org/issues/10600#change-55021

* Author: John Anderson
* Status: Assigned
* Priority: Normal
* Assignee: Koichi Sasada
----------------------------------------
In a multiple-producer / multiple-consumer situation using blocking enq and deq, closing a queue cleanly is difficult. It's possible using a queue poison token, but unpleasant because either producers have to know how to match up number of poison tokens with number of consumers, or consumers have to keep putting the poison back into the queue which complicates testing for empty and not blocking on deq.

This patch (from trunk at b2a128f) implements Queue#close which will close the queue to producers, leaving consumers to deq the remaining items. Once the queue is both closed and empty, consumers will not block. When an empty queue is closed, all consumers blocking on deq will be woken up and given nil.

With Queue#close, clean queue shutdown is simple:

~~~ ruby
queue = SizedQueue.new 1000

consumer_threads = lots_of.times.map do
  Thread.new do
    while item = queue.pop
      do_work item
    end
  end
end

source = somewhat_async_enumerator

producer_threads = a_few.times.map do
  Thread.new do
    loop{queue << source.next}
  end
end

producer_threads.each &:join
queue.close
consumer_threads.each &:join
~~~


---Files--------------------------------
queue-close.diff (5.18 KB)
queue-close-2.diff (10.2 KB)
patch-25f99aef.diff (25.2 KB)
queue_benchmark.rb (2.95 KB)


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