Java wait/notify/notifyAll for MRI and JRuby

gistfile1.txt

# Old school Java wait/notify

if defined?(RUBY_ENGINE) && RUBY_ENGINE == 'jruby'
  # Use Java wait/notify/notifyAll
  require "java"

  class Object

    def wait
      create_monitor unless @monitor
      @monitor.synchronized {
        @monitor.wait
      }
    end

    def notify
      create_monitor unless @monitor
      @monitor.synchronized {
        @monitor.notify
      }
    end

    def notify_all
      create_monitor unless @monitor
      @monitor.synchronized {
        @monitor.notify_all
      }
    end

    protected

    def create_monitor
      Thread.exclusive {
        # If the monitor was created by another thread, just exit
        return if @monitor
        @monitor = java.lang.Object.new
      }
    end

  end

else
  # Implement an equivalent in MRI

  class Object
    def wait
      create_monitor unless @monitor
      @monitor.synchronize {
        @waiting_threads << Thread.current
      }
      # Warning: Due to lack of language support in Ruby, the thead stop is outside synchronized block
      Thread.stop
    end
   
    def notify
      create_monitor unless @monitor
      if @monitor and @waiting_threads
        @monitor.synchronize {
          @waiting_threads.delete_at(0).run unless @waiting_threads.empty?
        }
      end
    end
   
    def notify_all
      create_monitor unless @monitor
      if @monitor and @waiting_threads
        @monitor.synchronize {
          @waiting_threads.each {|thread| thread.run}
          @waiting_threads = []
        }
      end
    end

    protected

    def create_monitor
      Thread.exclusive {
        # If the monitor was created by another thread, just exit
        return if @monitor
        @waiting_threads = [] unless @waiting_threads
        @monitor = Mutex.new unless @monitor_mutex
      }
    end

  end

end