Simple thread poll

demo.rb

require 'colorize'
# require 'thread/pool'

# pool = Thread.pool(3)
pool = ThreadPool.new 3
1.upto(10).to_a.each { |num|
  pool.process do
    sleep_for = (rand()*10).to_i
    text      = "#{num} sleep #{sleep_for}"

    puts "START #{text}".red
    sleep sleep_for
    puts "END #{text}".green
  end
}

pool.shutdown

thread_poll_2.rb

require 'thread'

class ThreadPool
  def initialize max_threads = 5
    @pool = SizedQueue.new max_threads
    max_threads.times{ @pool << 1 }
    @mutex = Mutex.new
    @running_threads = []
  end

  def process &block
    @pool.pop
    @mutex.synchronize do
      @running_threads << Thread.start do
        begin
          block.call
        rescue Exception => e
          puts "Exception: #{e.message}\n#{e.backtrace}"
        ensure
          @pool << 1
        end
      end
    end
  end

  def shutdown
    @running_threads.each &:join
  end
end

thread_pool.rb

class ThreadPool
  def initialize parallel
    @parallel = parallel
    @running  = 0
    @pool     = []
    @threads  = []
    @mutex    = Mutex.new # synchronize
  end

  def process func=nil, &block
    @pool.push func || block
  end

  def run!
    return shutdown unless @pool[0]

    if @running < @parallel
      @mutex.synchronize { @running += 1 }

      @threads << Thread.new {
        @pool.shift.call
        @mutex.synchronize { @running -= 1 }
      }
    else
      sleep 1.0/100
    end
    run!
  end

  def shutdown
    return run! if @pool[0]
    @threads.each(&:join)
  end
end