# File lib/rack/session/memcache.rb, line 78
      def with_lock(env, default=nil)
        @mutex.lock if env['rack.multithread']
        yield
      rescue MemCache::MemCacheError, Errno::ECONNREFUSED
        if $VERBOSE
          warn "#{self} is unable to find memcached server."
          warn $!.inspect
        end
        default
      ensure
        @mutex.unlock if @mutex.locked?
      end