thread-pool.rb

require 'concurrent'

pool = Concurrent::FixedThreadPool.new(8, idletime: nil)

100.times do |i|
  pool.post do
    rnd   = SecureRandom.random_number(5)
    puts "task #{i}: sleep #{rnd}"
    sleep rnd
  end
end

pool.shutdown
pool.wait_for_termination