    # File lib/active_support/vendor/memcache-client-1.5.0/memcache.rb, line 403
      def flush_all
        raise MemCacheError, 'No active servers' unless active?
        raise MemCacheError, "Update of readonly cache" if @readonly
        begin
          @mutex.lock if @multithread
          @servers.each do |server|
            begin
              sock = server.socket
              raise MemCacheError, "No connection to server" if sock.nil?
              sock.write "flush_all\r\n"
              result = sock.gets
              raise_on_error_response! result
              result
            rescue SocketError, SystemCallError, IOError => err
              server.close
              raise MemCacheError, err.message
            end
          end
        ensure
          @mutex.unlock if @multithread
        end
      end