Ruby parellel processing and inter-process messaging with fork

parallel_processor.rb

class ParallelProcessor
  attr_accessor :pid_params
  
  def initialize
    @pid_params = {}
  end

  def spawn_worker(start, finish, writer)
    pid = fork do
      puts "worker working on #{start} to #{finish}"
      (start..finish).each do |i|
        sleep rand(0.5) # do some work
        puts "finished #{i}"
        writer.puts
      end
      puts "#{start}-#{finish} finished!"
    end
    puts "started worker for #{start} to #{finish}"
    pid_params[pid] = [start, finish]
  end

  def run
    reader, writer = IO.pipe

    stuff_to_do = [ [1,10], [11,20], [21,30], [31,40], [41,50], [51,60], [61,70], [71,80], [81,90], [91,100] ]

    fork do
      completed = 0
      puts "progress bar process started"
      writer.close
      while !reader.eof?
        reader.readline
        completed += 1
        puts "finished #{completed} of 100 parts"
      end
    end
    reader.close
    
    running_workers = 0
    while !stuff_to_do.empty?
      start, finish = stuff_to_do.shift
      spawn_worker(start, finish, writer)
      running_workers += 1
      if running_workers >= 2
        pid = Process.wait
        puts "child #{pid} finished doing #{pid_params[pid]}"
        running_workers -= 1
      end
    end
  end
end

ParallelProcessor.new.run