From: Aaron Patterson <tenderlove@...>
Date: 2012-04-14T11:08:46+09:00
Subject: [ruby-core:44355] Re: [ruby-trunk - Feature #6293][Open] new queue / blocking queues


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On Sat, Apr 14, 2012 at 10:23:56AM +0900, Eric Wong wrote:
> "tenderlovemaking (Aaron Patterson)" <aaron@tenderlovemaking.com> 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.
>=20
> I don't think queues should be limited to strictly
> blocking/non-blocking.
>=20
> 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:
>=20
>   while task =3D queue.take
>     while task.run_one_timeslice
>=20
>       if pending_task =3D queue.trytake # non-blocking
>=20
>         # reschedule task if another task shows up
>         queue.push(task)
>         task =3D pending_task
>       end
>=20
>     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 =3D Thread::BlockingQueue.new

    while task =3D queue.shift
      while task.run_one_timeslice
   =20
        if pending_task =3D queue.poll # non-blocking
   =20
          # reschedule task if another task shows up
          queue.push(task)
          task =3D pending_task
        end
   =20
      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. :-)

--=20
Aaron Patterson
http://tenderlovemaking.com/

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