From: Justin Collins <justincollins@...>
Date: 2007-11-07T03:47:24+09:00
Subject: Re: ruby thread newbie problem

Bram Kuijper wrote:
> Hi all,
>
> As a ruby newbie, I am trying to have two Threads process the
> contents of one Queue. However, in my code only one Thread is processing
> the contents of Queue, instead of both Threads. How can I make sure that
> _both_ Threads process the Queue mentioned below?
>
>
> This is my code:
>
> queue = Queue.new
> queue << "$contents_of_queue"
> queue << "$contents_of_queue"
> queue << "$contents_of_queue"
>
> threads = []
>
> 2.times do |thread_index|
>     threads[thread_index] =
>         Thread.new(thread_index) do | this_thread_name |
>        
>     # let each Thread work with things from the queue
>     while ! queue.empty?   
>
>             contents_of_queue = queue.deq
>
>             # output Thread number
>             puts "executing #{contents_of_queue} " \
>                 + "by thread #{this_thread_name}"
>
>         end
>     end   
> end
>
> This code will output:
> "executing $contents_of_queue by thread 0"
> "executing $contents_of_queue by thread 0"
> "executing $contents_of_queue by thread 0"
>
> my question is: why will thread 1 never show up?
>
> thanks,
> Bram

Thread 1 isn't showing up because Thread 0 empties the queue before 
Thread 1 even gets to run.
Before

while ! queue.empty?

add

puts "This is thread #{this_thread_name}"

and you'll see that they do both run, it's just the second thread 
doesn't need to do anything.

-Justin