Worker pool in Ruby

worker_pool.rb

# from https://hspazio.github.io/2017/worker-pool/

SIZED_QUEUE_SIZE = 10

############################################################################
def fib(n)
  n < 2 ? n : fib(n-1) + fib(n-2)
end

############################################################################
class Worker
  attr_reader :name

  def initialize(name)
    @name = name
    @queue = SizedQueue.new(SIZED_QUEUE_SIZE)
    @thread = Thread.new { perform }
  end

  def <<(job)
    @queue << job
  end

  def jobs_count
    @queue.size
  end

  def join
    @thread.join
  end

  private

  def perform
    while (job = @queue.pop)
      break if job == :done
      job.call
      puts "#{name} got #{job}" # only for debugging
    end
  end
end

############################################################################
class LeastBusyFirstScheduler
  def initialize(workers)
    @workers = workers
  end

  def schedule(job)
    worker = @workers.sort_by(&:jobs_count).first
    worker << job
  end
end

############################################################################
class WorkerPool
  def initialize(num_workers, scheduler_factory)
    @workers = Array.new(num_workers) { |n| Worker.new("worker_#{n}") }
    @scheduler = scheduler_factory.new(@workers)
  end

  def <<(job)
    if job == :done
      @workers.map { |worker| worker << :done }
    else
      @scheduler.schedule(job)
    end
  end

  def wait
    @workers.map(&:join)
  end
end

############################################################################
pool = WorkerPool.new(5, LeastBusyFirstScheduler)
results = {}

Thread.new do
  30.times { |n| pool << -> { results[n] = fib(n+20) } }
  pool << :done
end

pool.wait
puts results

CRuby (GIL):
$ rvm 2.5.1
$ ruby worker_pool.rb

JRuby (real threads):
$ rvm jruby-9.1.7.0
$ ruby worker_pool.rb