面试题：在分布式系统，你能想出来几种生成唯一ID的方案？(14)_系统唯一ID是我们在设计一个系统的时候

{
sequence = 0L;

lastTimestamp = timestamp;

return ((timestamp - twepoch) << (int)timestampLeftShift) | (datacenterId << (int)datacenterIdShift) | (workerId << (int)workerIdShift) | sequence;

protected long tilNextMillis(long lastTimestamp)
{
long timestamp = timeGen();
while (timestamp <= lastTimestamp)
{
timestamp = timeGen();