gistfile1.rb

require 'thread'
require 'timeout'

class ObjectPool
  attr_reader :max
  attr_accessor :timeout
  attr_accessor :create
  attr_accessor :objects
  attr_accessor :used
  
  def initialize(*args, &block)
    @max = Integer(args.shift || 10)
    @timeout = nil
    @objects = []
    @used = {}
    @mutex = Mutex.new
    @cond  = ConditionVariable.new
    @create = block
  end
    
  def get(&block)
    object = nil
    @mutex.synchronize {
      if !@objects.empty?
        object = @objects.pop
      elsif @used.size < @max
        object = create ? create.call : nil
      else
        Timeout.timeout(@timeout){ @cond.wait(@mutex) }
        object = @objects.pop
      end
      @used.store(object.__id__, object)
    }
    if block
      begin
        block.call(object)
      ensure
        release(object)
      end
    else
      object
    end
  end

  def release(object)
    @mutex.synchronize {
      @used.delete(object.__id__)
      @objects.push(object)
      @cond.signal
    }
    object
  end
  
  def max=(size)
    @mutex.synchronize {
      if @objects.size + @used.size > size
	raise ArgumentError.new("Cannot change max size to %d. There are objects over the size." % size)
      end
      @max = size
    }
    size
  end
end


if $0 == __FILE__

  pool = ObjectPool.new{ Array.new }

  n = 2**16

  Thread.new do
    Thread.current.abort_on_exception=true
    n.times{ 10.times{ pool.get{} } }
  end

  n.times do
    Thread.new do
      Thread.current.abort_on_exception=true
      sleep rand

      Thread.new do
        Thread.current.abort_on_exception=true
        sleep rand
        pool.get do |array|
          array.push Thread.current.object_id
        end
      end
    end
  end

  Thread.list.map{|t| t.join unless Thread.current==t}

  values = pool.objects.flatten

  p values.size
  p values.uniq.size
end