# Oleg Andreev <oleganza@gmail.com>
# November 3, 2008

require 'thread'
module DataMapper
  class Repository
    # Original context returns new context stack for the current thread:
    #   Thread.current[:dm_repository_contexts] ||= []
    # This is not cool because there might be new thread creation on each request,
    # what turns into tons of stacks and repositories generated for each request.
    class ContextsPool

      THREAD_VAR = :dm_repository_contexts

      # Ensures that THREAD_VAR is used.
      module OverrideContext
        def context
          Thread.current[THREAD_VAR]
        end
      end

      def initialize(options = {})
        options = options.merge(:size => 2, :clean_interval => 120)
        size = options[:size]
        int = options[:clean_interval]

        @queue = Queue.new
        size.times{ @queue.push([]) }
        Repository.extend(OverrideContext)

        @cleaner = Thread.new(size, int) do |s, i|
          sleep i
          q = Queue.new
          s.times { q.push([]) }
          @queue = q
        end
      end

      # Merb Usage:
      #
      # CTX_POOL_SIZE = 10 # number of IdentityMaps per process
      # CTX_POOL = DataMapper::Repository:ContextsPool.new(CTX_POOL_SIZE)
      #
      # def _call_action(*args)
      #   CTX_POOL.wrap do
      #     repository do
      #       # time out the action if it takes longer than 1 second
      #       SystemTimer.timeout(1) do
      #         super
      #       end
      #     end
      #   end
      # end
      #
      def wrap
        prev = Thread.current[THREAD_VAR]
        q = @queue # @queue can be changed by @cleaner, therefore we use local reference
        Thread.current[THREAD_VAR] = q.pop
        yield
      ensure
        q.push(Thread.current[THREAD_VAR])
        Thread.current[THREAD_VAR] = prev
      end

    end
  end
end