Ruby parallel run slow commands with Thread pool

ruby-thread-pool.rb

# gem 'thread'
require 'thread/pool'

pool = Thread.pool(20)
total = 10000
total.times do |i|
  pool.process do
    stdout = ""
    stdout << "\n"
    stdout << "Queue #{i}/#{total}"
    stdout << `./run-slow-command` + "\n"
    stdout << "------------------------------------------------------------------\n"
    puts stdout
  end
end
pool.shutdown