rpool.rb

class RPool

	attr_accessor :max_size
	attr_reader :workers

	def initialize(max_size = 128)
		@max_size = max_size
		@workers = Array.new
		@mutex = Mutex.new
	end

	def size()
		@mutex.synchronize{ @workers.size }
	end

	def busy?()
		@mutex.synchronize{ @workers.any?{|w| w.busy?} }
	end

	# prevent program from exiting while
	# there are working workers
	def join()
		sleep 0.01 while busy?
	end

	# do something
	def do(&b)
		wait_for_worker.set_job(&b)
	end

	def wait_for_worker()
		while true
			#find free worker, or create one
			worker = @mutex.synchronize{ get_free_worker || create_worker }
			return worker if worker
			sleep 0.01
		end
	end

	def get_free_worker
		@workers.each {|w| return w unless w.busy?}; nil
	end

	def create_worker
		return nil if @workers.size >= @max_size
		worker = RWorker.new nil
		@workers << worker
		worker
	end

end

rworker.rb

class RWorker

	def initialize(&b)
		@mutex = Mutex.new #for accessing block in thread
		@job = &b
	end


	def run()
		@thread = Thread.new do
			while true
				sleep 0.001
				job = @mutex.synchronize{@job}
				if !job.nil?
					job.call #Run task
					@mutex.synchronize{@job = nil} #Then remove job
				else
					sleep 0.01 #Waiting for a job
				end
			end
		end
	end

	def busy?()
		@mutex.synchronize{ !@job.nil? }
	end

	def set_job(&b)
		@mutex.synchronize do
			if @block
				@block = &b
			else
				raise RuntimeError, "Thread is busy."
			end
		end
	end

end