class Concurrent::FixedThreadPool

def <<(block)
  self.post(&block)
  return self
end

def clean_pool
  @pool.reject! {|worker| worker.dead? } 
end

def create_worker_thread
  wrkr = Worker.new(@queue, self)
  Thread.new(wrkr, self) do |worker, parent|
    Thread.current.abort_on_exception = false
    worker.run
    parent.on_worker_exit(worker)
  end
  return wrkr
end

def drain_pool
  @pool.each {|worker| worker.kill }
  @pool.clear
end

def fill_pool
  return unless @state == :running
  while @pool.length < @max_threads
    @pool << create_worker_thread
  end
end

def initialize(size, opts = {})
  @max_threads = size || MAX_POOL_SIZE
  if @max_threads < MIN_POOL_SIZE || @max_threads > MAX_POOL_SIZE
    raise ArgumentError.new("size must be from #{MIN_POOL_SIZE} to #{MAX_POOL_SIZE}")
  end
  @state = :running
  @pool = []
  @terminator = Event.new
  @queue = Queue.new
  @mutex = Mutex.new
end

def kill
  @mutex.synchronize do
    break if @state == :shutdown
    @state = :shutdown
    @queue.clear
    drain_pool
    @terminator.set
  end
end

def length
  @mutex.synchronize do
    @state == :running ? @pool.length : 0
  end
end

def on_end_task(worker)
  @mutex.synchronize do
    break unless @state == :running
    clean_pool
    fill_pool
  end
end

def on_start_task(worker)
end

def on_worker_exit(worker)
  @mutex.synchronize do
    @pool.delete(worker)
    if @pool.empty? && @state != :running
      @state = :shutdown
      @terminator.set
    end
  end
end

def post(*args, &block)
  raise ArgumentError.new('no block given') if block.nil?
  @mutex.synchronize do
    break false unless @state == :running
    @queue << [args, block]
    clean_pool
    fill_pool
    true
  end
end

def running?
  return @state == :running
end

def shutdown
  @mutex.synchronize do
    break unless @state == :running
    if @pool.empty?
      @state = :shutdown
      @terminator.set
    else
      @state = :shuttingdown
      @pool.length.times{ @queue << :stop }
    end
  end
end

def wait_for_termination(timeout = nil)
  return @terminator.wait(timeout)
end