public class SnowflakeIdGenerator {
private final long twepoch = 1609459200000L; // 2021-01-01 00:00:00
private final long workerIdBits = 5L;
private final long datacenterIdBits = 5L;
private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
private final long sequenceBits = 12L;
private final long workerIdShift = sequenceBits;
private final long datacenterIdShift = sequenceBits + workerIdBits;
private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
private final long sequenceMask = -1L ^ (-1L << sequenceBits);
private long workerId;
private long datacenterId;
private long sequence = 0L;
private long lastTimestamp = -1L;
public SnowflakeIdGenerator(long workerId, long datacenterId) {
if (workerId > maxWorkerId || workerId < 0) {
throw new IllegalArgumentException("Worker ID out of range");
}
if (datacenterId > maxDatacenterId || datacenterId < 0) {
throw new IllegalArgumentException("Datacenter ID out of range");
}
this.workerId = workerId;
this.datacenterId = datacenterId;
}
public synchronized long nextId() {
long timestamp = timeGen();
if (timestamp < lastTimestamp) {
throw new RuntimeException("Clock moved backwards");
}
if (timestamp == lastTimestamp) {
sequence = (sequence + 1) & sequenceMask;
if (sequence == 0) {
timestamp = tilNextMillis(lastTimestamp);
}
} else {
sequence = 0L;
}
lastTimestamp = timestamp;
return ((timestamp - twepoch) << timestampLeftShift)
| (datacenterId << datacenterIdShift)
| (workerId << workerIdShift)
| sequence;
}
private long timeGen() {
return System.currentTimeMillis();
}
private long tilNextMillis(long lastTimestamp) {
long timestamp = timeGen();
while (timestamp <= lastTimestamp) {
timestamp = timeGen();
}
return timestamp;
}
}
2.3 时钟回拨处理
java复制代码
public synchronized long nextId() {
long timestamp = timeGen();
if (timestamp < lastTimestamp) {
long offset = lastTimestamp - timestamp;
if (offset <= 5) {
try {
wait(offset << 1);
timestamp = timeGen();
if (timestamp < lastTimestamp) {
throw new RuntimeException("Clock moved backwards");
}
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
} else {
throw new RuntimeException("Clock moved backwards too much");
}
}
if (timestamp == lastTimestamp) {
sequence = (sequence + 1) & sequenceMask;
if (sequence == 0) {
timestamp = tilNextMillis(lastTimestamp);
}
} else {
sequence = 0L;
}
lastTimestamp = timestamp;
return ((timestamp - twepoch) << timestampLeftShift)
| (datacenterId << datacenterIdShift)
| (workerId << workerIdShift)
| sequence;
}
public class RedisIdGenerator {
private final StringRedisTemplate redisTemplate;
private final String keyPrefix = "sequence:";
private final long step = 100;
public long nextId(String bizType) {
String key = keyPrefix + bizType;
Long current = redisTemplate.opsForValue().increment(key);
if (current <= step) {
redisTemplate.opsForValue().set(key, String.valueOf(current + step * 10));
}
return current;
}
}
4.2 Lua脚本保证原子性
lua复制代码
local key = KEYS[1]
local step = tonumber(ARGV[1])
local current = redis.call('INCR', key)
if current <= step then
redis.call('SET', key, current + step * 10)
end
return current