From: Robert Klemme <shortcutter@...>
Date: 2006-06-04T22:41:19+09:00
Subject: Re: SizedQueue

2006/6/3, Paul Tsung <ptsung@gmail.com>:
> Does anyone know about threads and SizedQueue?
>
> I want to limit or control the number of threads created in a script.  I
> am not sure what is the best way to handle this.

You probably haev a misconception on how a SizedQueue works. The limit
on the queue ensures that at most n elements reside in the queue at
any given point in time. You typically do that if the queue is filled
faster than it is emptied. When the queue is full an enqueue operation
blocks the calling thread.

What you probably want is a leigth weight processing framework.  The
basic idea is to have a single queue (sized limited or not) and a
fixed number of threads reading from the queue.

A typical setting:

require 'thread'

MAX_THREADS = 10
QUEUE = Queue.new

threads = (1..MAX_THREADS).map do |i|
  Thread.new(QUEUE) do |q|
    until ( q == ( task = q.deq ) )
      # process task
      print "thread-", i, " ", task.inspect, "\n"
    end
  end
end

# generate tasks
1000.times {|i| QUEUE.enq i}

# send terminators down the queue
threads.size.times { QUEUE.enq QUEUE}

# wait for threads to finish
threads.each {|t| t.join}

# eof

HTH

robert



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