Small sample program to illustrate process management in ruby

proctest.rb

#!/usr/bin/env ruby
require 'set'

class Monitor
  @@max_procs = 3

  def initialize(worker_class)
    @worker = worker_class.new
    @interrupted = false
    @threads = []
  end

  def run
    trap("INT") { @interrupted = true }
    
    puts "Monitor #{Process.pid} started"



    @@max_procs.times do |thread_num|
      puts "Starting Monitor Thread #{thread_num}"
  
      thread = Thread.new do
        Thread.current[:num] = thread_num
        puts "Monitor #{current_thread_num} started"
        while !@interrupted
          puts "Monitor #{current_thread_num} new iteration"
          pid = spawn_child
          wait_child(pid)
        end
        puts "Monitor #{current_thread_num} stopped"
      end
      
      @threads << thread
    end
    
    while threads_remaining
      sleep(0.1)
    end
    
  end
  
  def threads_remaining
    @threads.find {|t| t.status}
  end
  
  def current_thread_num
    Thread.current[:num]
  end
  
  def wait_child(pid)
    puts "Monitor #{current_thread_num} waiting for Worker #{pid}"    
    Process.wait(pid)
    puts "Monitor #{current_thread_num} received exit from Worker #{pid}"
  end
  
  def spawn_child
    if pid = Process.fork()
      puts "Monitor #{current_thread_num} spawned Worker #{pid}"
      return pid
    else
      puts "\t Worker (Monitor #{current_thread_num}) #{Process.pid} starting"
      @worker.run
      puts "\t Worker (Monitor #{current_thread_num}) #{Process.pid} exiting"
      exit
    end
  end
end

class Worker
  
  def rand_time
    byte = 0
    File.open('/dev/random', 'r') do |f|
      byte += f.getbyte
      byte += f.getbyte
      byte += f.getbyte
      byte += f.getbyte
    end
    byte / 1000.0
  end
  
  def run
    puts "\t Worker #{Process.pid} started"
    time = 3 * rand_time
    puts "\t Worker #{Process.pid} sleeping #{time}"
    sleep(time)
  end
end

monitor = Monitor.new(Worker)
monitor.run