code: func (lr *LockedRand) Read(p []byte) (n int, err error) {
  	lr.lk.Lock()
  	n, err = lr.r.Read(p)
  	lr.lk.Unlock()
  	return
  }
docs: // Read generates len(p) random bytes and writes them into p. It
  // always returns len(p) and a nil error.
  // Read should not be called concurrently with any other Rand method.