From: Robert Klemme <shortcutter@...>
Date: 2009-05-28T01:11:42+09:00
Subject: Re: Newbie on Threads

2009/5/27 Nabs Kahn <nabusman@gmail.com>:
> This is what I ended up doing, similar to what was suggested.
> (definition of screenScrape method not included)

Thanks for the update!

> bufferSize = 10
> buffer = SizedQueue.new(bufferSize)
> threads = []
>
> producer = Thread.new do
>  File.open("urls.txt").each do |url|
>    buffer.enq url
>  end
>  bufferSize.times {buffer.enq(:END_OF_WORK)}
> end
>
> bufferSize.times do
>  threads << Thread.new do
>    url = nil
>    while(url != :END_OF_WORK)
>      url = buffer.deq
>      screenScrape(url)
>    end
>  end
> end

The loop above does not work properly because you will hand off
:END_OF_WORK to screenScrape().  Rather do

 threads << Thread.new do
   while ((url = buffer.deq) != :END_OF_WORK)
     screenScrape(url)
   end
 end

or

 threads << Thread.new do
   until ((url = buffer.deq) == :END_OF_WORK)
     screenScrape(url)
   end
 end

> producer.join
> threads.each do |thr|
>  thr.join
> end

Btw, you do not need a separate producer thread.  You can simply do
that in the main thread.  But of course you must start worker threads
before you start to fill the queue.

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/