From: Wesley J Landaker <wjl@...>
Date: 2001-08-07T07:31:21+09:00
Subject: [ruby-talk:19256] Re: Trying to get to grips with Ruby threads

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On Monday 06 August 2001  3:21pm, Peter Hickman wrote:
> I am trying to get to grips with threads in Ruby and I wrote (adapted
> more like) the following code. What happens is each thread processes
> in turn with everything pausing on the sleep in thread id 0. What I
> was expecting was thread 0 would sleep and thread 1 would eat up all
> the work, or at least a fair amount of it. But thread 1 does not seem
> to run until thread 0 finishes and then it goes back to thread 0.
>
> Threads can do what I'm asking of them can't they? I need to do it in
> this manner as each thread will infact also be adding work into the
> work array. Thus forking would seem to be out of the question. A clue
> please.
>
> require 'thread'
> mutex = Mutex.new
>
> cv = ConditionVariable.new
>
> work = Array.new
> 100.times {|i| work << "Job #{i}" }
>
> threads = Array.new
>
> 2.times {|i|
>  threads << Thread.new(i) {|id|
>   mutex.synchronize {
>    while 1 == 1 do
>     cv.wait(mutex)
>     if ! work.empty? then
>      job = work.pop
>      cv.signal
>      puts "Thread #{id} processing #{job}\n"
>      if id == 0 then
>       sleep(5)
>      end
>     else
>      cv.signal
>      break
>     end
>    end
>   }
>  }
> }
>
> cv.signal
>
> threads.each {|i| i.join }

Sleeping does not release the mutex... so thread #1 is always going to 
be waiting for thread #0 to stop sleeping, as thread #0 owns the mutex.

- -- 
Wesley J. Landaker - wjl@mindless.com
http://www.landaker.net            PGP DSS/DH Key: 0x0F338E07
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