From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-07-07T01:15:21+09:00
Subject: Re: Problem of share variable in function using thread

On Tue, Jul 6, 2010 at 6:00 PM, Nita Neou <sophoah@gmail.com> wrote:
> Hi All
>
> I got a little problem when using thread function and variable, let's
> say this code :
>
> require 'rubygems'
> require 'watir'
> require 'thread'
>
> def testfunc(id)
>        total = id + 5
>        puts "id #{id} is #{total}"
> end
>
> threads = []
> numberlist = [1, 2, 3]
> for id in numberlist
>        threads << Thread.new {testfunc(id)}
> end
>
> threads.each { |aThread|  aThread.join }
>
> my output is :
> [sophoah@fedora ]$ ruby test.rb
> id 3 is 8
> id 3 is 8
> id 3 is 8
>
> The fact is that I would like this output :
> id 1 is 6
> id 2 is 7
> id 3 is 8
>
> I am suspecting that all variable id, and total are all share among
> all the thread, is that right ? why ? I thought variable in a block
> were not share among variable ? How can I fix this problem ?

Blocks in Ruby are closures, this means that inside the block you pass
to Thread.new, the variable id is the same.
The Thread class has a way to avoid this, take a look at the constructor:

http://ruby-doc.org/core/classes/Thread.html#M000437

You can pass parameters to #new and it will pass them to the block.
You can use this technique to use a variable in the block that is
different for each thread, like this:

def testfunc(id)
  total = id + 5
  puts "id #{id} is #{total}"
end

threads = []
numberlist = [1, 2, 3]
for id in numberlist
 threads << Thread.new(id) {|my_id| testfunc(my_id)}
end

threads.each { |aThread|  aThread.join }


$ ruby threads.rb
id 1 is 6
id 2 is 7
id 3 is 8


Jesus.