code: func bumpLastUpdate(loc *int64, newVal int64) {
  	prev := atomic.SwapInt64(loc, newVal)
  	for prev > newVal {
  		newVal = prev
  		prev = atomic.SwapInt64(loc, newVal)
  	}
  }
docs: // bumpLastUpdate increases lastUpdate.
  // note:
  // * received point may be older than a previously received point, in which case the previous value was correct
  // * someone else may have just concurrently updated lastUpdate to a higher value than what we have, which we should restore
  // * by the time we look at the previous value and try to restore it, someone else may have updated it to a higher value
  // all these scenarios are unlikely but we should accommodate them anyway.