A small, probably bad Thread Pool written in the service of reproducing a bug.

thread_pool.rb

require 'thread'

module ThreadPool

  class Executor

    def initialize(queue)
      @queue = queue
      @thread = nil
    end

    def start
      @thread = Thread.tap { |t| t.abort_on_exception = true }.new do
        loop do
          @queue.shift.call
        end
      end
    end

    def stop
      @thread.exit if @thread
    end

  end

  class Pool

    def initialize(limit)
      @queue = Queue.new
      @limit = limit
      @executors = limit.times.map { Executor.new(@queue).tap(&:start) }
    end

    def execute(&block)
      loop do
        if full?
          # Disclaimer: I don't know if this how one is supposed to use Thread.pass, but it seems right, based on the docs.
          Thread.pass
        else
          break
        end
      end

      @queue.push(block)
    end

    def size
      @queue.size
    end

    def empty?
      size == 0
    end

    def full?
      size >= @limit
    end

    def stop
      @executors.each(&:stop)
    end

  end

end

thread_pool_usage.rb

pool = ThreadPool::Pool.new(10)

100.times do
  pool.execute do
    # do something!
  end
end