code: func MemLocker(c context.Context) Locker {
  	return &memLocker{
  		clientID: strings.Join([]string{
  			"datastore_cache",
  			info.RequestID(c),
  		}, "\x00"),
  	}
  }
docs: // MemLocker returns a Locker instance that uses a memcache lock bound to the
  // current request ID.