    # File lib/rack/session/memcache.rb, line 29
          def initialize(app, options={})
            super

            @mutex = Mutex.new
            mserv = @default_options[:memcache_server]
            mopts = @default_options.reject{|k,v| !MemCache::DEFAULT_OPTIONS.include? k }

            @pool = options[:cache] || MemCache.new(mserv, mopts)
            unless @pool.active? and @pool.servers.any?{|c| c.alive? }
              raise 'No memcache servers'
            end
          end