gistfile1.rb

# Runs the given array of +commands+ in parallel. The amount of spawned
# simultaneous jobs is determined by the `j' env variable and defaults to 1.
def parallel_execute(commands)
  @jobs ||= ENV['j'] ? ENV['j'].to_i : 1
  queue = Queue.new
  queue = commands.each { |command| queue << command }

  Array.new(@jobs) do
    Thread.new do
      while command = queue.shift
        sh command
      end
    end
  end.each { |t| t.join }
end