    # File lib/phusion_passenger/abstract_server_collection.rb, line 260
            def cleanup
                    must_not_be_in_synchronize_block
                    @cleanup_lock.synchronize do
                            return if @done
                            @lock.synchronize do
                                    @done = true
                                    @cond.signal
                            end
                            @cleaner_thread.join
                            synchronize do
                                    clear
                            end
                    end
            end