Noosfero/noosfero

# based on https://github.com/discourse/discourse/blob/master/lib/scheduler/defer.rb

module Noosfero
  module Scheduler
    module Deferrable
      def initialize
        # FIXME: do some other way when not using Unicorn
        (@async = (not Rails.env.test?)) && defined? Unicorn
        @queue = Queue.new
        @mutex = Mutex.new
        @paused = false
        @thread = nil
      end

      def pause
        stop!
        @paused = true
      end

      def resume
        @paused = false
      end

      # for test
      def async=(val)
        @async = val
      end

      def later(desc = nil, &blk)
        if @async
          start_thread unless (@thread && @thread.alive?) || @paused
          @queue << [blk, desc]
        else
          blk.call
        end
      end

      def stop!
        @thread.kill if @thread && @thread.alive?
        @thread = nil
      end

      # test only
      def stopped?
        !(@thread && @thread.alive?)
      end

      def do_all_work
        while !@queue.empty?
          do_work _non_block = true
        end
      end

      private

        def start_thread
          @mutex.synchronize do
            return if @thread && @thread.alive?

            @thread = Thread.new do
              while true
                do_work
              end
            end
            @thread.priority = -2
          end
        end

        # using non_block to match Ruby #deq
        def do_work(non_block = false)
          job, desc = @queue.deq non_block
          begin
            job.call
          rescue => ex
            ExceptionNotifier.notify_exception ex, message: "Running deferred code '#{desc}'"
          end
        rescue => ex
          ExceptionNotifier.notify_exception ex, message: "Processing deferred code queue"
        end
    end

    class Defer
      module Unicorn
        def process_client(client)
          ::Noosfero::Scheduler::Defer.pause
          super client
          ::Noosfero::Scheduler::Defer.do_all_work
          ::Noosfero::Scheduler::Defer.resume
        end
      end

      extend Deferrable
      initialize
    end
  end
end