[ruby-core:44355] Re: [ruby-trunk - Feature #6293][Open] new queue / blocking queues

On Sat, Apr 14, 2012 at 10:23:56AM +0900, Eric Wong wrote:
> "tenderlovemaking (Aaron Patterson)" <[e-mail]> wrote:
> > Whenever I use queues, I either use them in a blocking or non-blocking
> > manner only, so I have separated them in to two classes Thread::Queue,
> > and Thread::BlockingQueue.
> 
> I don't think queues should be limited to strictly
> blocking/non-blocking.
> 
> Outside of Ruby, but I've occassionally needed queues that could
> toggle between blocking/non-blocking (even in the same thread)
> to enforce some sort of fairness.  Something like:
> 
>   while task = queue.take
>     while task.run_one_timeslice
> 
>       if pending_task = queue.trytake # non-blocking
> 
>         # reschedule task if another task shows up
>         queue.push(task)
>         task = pending_task
>       end
> 
>     end
>   end

The patch I submitted includes a method `poll` which will not block if a
timeout isn't supplied.  In your case, I would rewrite as:

    queue = Thread::BlockingQueue.new

    while task = queue.shift
      while task.run_one_timeslice
    
        if pending_task = queue.poll # non-blocking
    
          # reschedule task if another task shows up
          queue.push(task)
          task = pending_task
        end
    
      end
    end

> Also, I very often use queues (often Unix pipes) where one end is
> blocking and the other end is not (though you don't implement
> non-blocking push at all)

Both of these queues should have non-blocking push since neither is
bounded.  If this patch is applied, I'll add sized queues which can
block. :-)

-- 
Aaron Patterson
http://tenderlovemaking.com/