Ruby Object Pool

object_pool.rb

# Module that handles object pool behaviour
# for you.
#
# Usage:
#   class Thing
#     extend Pool
#
#     def initialize a, b, c
#       @a, @b, @c = a, b, c
#     end
#   end
#   thing = Thing.obtain 1, 2, 3
#   thing.release
#   thing = Thing.obtain 4, 5, 6
#   Thing.release_all # Releases all managed instances.
#   Pool.release_all # Releases all managed instances in all pools.
#
module Pool
  
  class << self
    require 'set'
    @@pools = Set.new
    
    # Add a Pool to the managed pools.
    #
    def add klass
      @@pools << klass
    end
    
    # Releases all obtained objects.
    #
    def release_all
      @@pools.each { |pool| pool.release_all }
    end
    
  end
  
  def self.extended klass
    add klass
    
    class << klass
      
      # Clear the free and used.
      #
      def clear
        @__free__ = []
        @__used__ = []
      end
         
      # Obtain creates a new reference if there is no free one
      # and uses an existing one if there is.
      #
      # (Any caches should be cleared using clear TODO in all initializers)
      #
      def obtain *args, &block
        unless reference = @__free__.shift
          reference = allocate
        end
        reference.send :initialize, *args, &block
        @__used__ << reference
        reference
      end
    
      # Releasing an instance adds it to the free pool.
      # (And removes it from the used pool)
      #
      def release instance
         @__free__ << instance
         @__used__.delete instance # TODO Optimize
      end
    
      # After you have called release all, you can't
      # use any reference that has formerly been obtained
      # anymore.
      #
      def release_all
        @__used__.each { |used| @__free__ << used } # TODO Optimize
        @__used__.clear
      end
    
      # How many obtainable objects are there?
      #
      def free_size
        @__free__.size
      end
    
      # How many used objects are there?
      #
      def used_size
        @__used__.size
      end
    end
    
    # Initialize the pool.
    #
    klass.clear
  
    # Pooled objects can be released using
    #   object.release
    #
    # Note: Do not use the object in any form after the release.
    #
    klass.send :define_method, :release do
      klass.release self
    end
    
  end
  
end