From: Edwin Fine <efine145-nospam01@...>
Date: 2006-11-25T14:42:45+09:00
Subject: Re: newbie question regarding threads and system commands

This is one possible solution, which seems to work fine (it takes 3.14 
seconds on my system to ping 3 web sites). Bottom line: you need to keep 
a list of the threads and join all of them in the calling code. Hope 
this helps. I recommend that you get a copy of the "Pickaxe" book 
(Programming Ruby: The Pragmatic Programmers Guide, 2nd edition) , which 
has a very good section on threading and lots of examples. In the 
meantime, you can read this from the first edition:

http://www.rubycentral.com/book/tut_threads.html
-------------
require 'thread'

class SystemExecutor
  # Returns array [[cmd, response], [cmd, response], ...]
  def SystemExecutor.run(system_cmd_list)
    thread_list = []
    system_response_list = []
    srl_mutex = Mutex.new

    system_cmd_list.each do |cmd|
      thread_list << Thread.new do
        begin
          response = %x{ #{cmd} }
          srl_mutex.synchronize do
            system_response_list << [cmd, response]
          end
        rescue Exception => exc
          srl_mutex.synchronize do
            system_response_list << [cmd, exc]
          end
        end
      end
    end

    thread_list.each { |thr| thr.join }
    system_response_list
  end
end

puts "Starting ping"
start_time = Time.now
resp = SystemExecutor.run(['ping www.ruby-forum.org', 'ping 
www.sourceforge.net', 'ping www.google.com'])
elapsed_time = Time.now - start_time

resp.each do |cmd, resp|
  puts "Command: #{cmd}", '-' * 20
  puts "Response:\n", '-' * 20, "#{resp}"
end

puts "Elapsed time: #{elapsed_time} seconds."

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