top.openyuan.jpa.id.snowflake.SnowflakeGenerationStrategy Maven / Gradle / Ivy
package top.openyuan.jpa.id.snowflake;
import top.openyuan.jpa.common.util.SystemClockUtils;
import java.net.InetAddress;
import java.util.concurrent.ThreadLocalRandom;
/**
* 基于Twitter的Snowflake算法实现分布式高效有序ID生产黑科技(sequence)——升级版Snowflake
*
* @author lzy
* @since v1.0.0
*/
public class SnowflakeGenerationStrategy {
private static volatile SnowflakeGenerationStrategy instance = null;
/**
* 起始时间戳
**/
private final static long START_TIME = 1631769292000L;
/**
* dataCenterId占用的位数：2
**/
private final static long DATA_CENTER_ID_BITS = 2L;
/**
* workerId占用的位数：8
**/
private final static long WORKER_ID_BITS = 8L;
/**
* 序列号占用的位数：12（表示只允许workId的范围为：0-4095）
**/
private final static long SEQUENCE_BITS = 12L;
/**
* workerId可以使用范围：0-255
**/
private final static long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);
/**
* dataCenterId可以使用范围：0-3
**/
private final static long MAX_DATA_CENTER_ID = ~(-1L << DATA_CENTER_ID_BITS);
private final static long WORKER_ID_SHIFT = SEQUENCE_BITS;
private final static long DATA_CENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;
private final static long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATA_CENTER_ID_BITS;
/**
* 用mask防止溢出:位与运算保证计算的结果范围始终是 0-4095
**/
private final static long SEQUENCE_MASK = ~(-1L << SEQUENCE_BITS);
private final long workerId;
private final long dataCenterId;
private long sequence = 0L;
private long lastTimestamp = -1L;
private static byte LAST_IP = 0;
private final boolean clock;
private final long timeOffset;
private final boolean randomSequence;
private final ThreadLocalRandom tlr = ThreadLocalRandom.current();
/**
* 采用单例模式初始化雪花帮助类，采用线程安全模式.
**/
public static SnowflakeGenerationStrategy getInstance(long dataCenterId){
if(instance == null){
synchronized(SnowflakeGenerationStrategy.class){
if(instance == null){
instance = new SnowflakeGenerationStrategy(dataCenterId);
}
}
}
return instance;
}
public SnowflakeGenerationStrategy(long dataCenterId) {
this(dataCenterId, 0x000000FF & getLastIPAddress(), false, 5L, false);
}
public SnowflakeGenerationStrategy(long dataCenterId, boolean clock, boolean randomSequence) {
this(dataCenterId, 0x000000FF & getLastIPAddress(), clock, 5L, randomSequence);
}
/**
* 基于Snowflake创建分布式ID生成器
*
* @param dataCenterId 数据中心ID,数据范围为0~255
* @param workerId 工作机器ID,数据范围为0~3
* @param clock true表示解决高并发下获取时间戳的性能问题
* @param timeOffset 允许时间回拨的毫秒量,建议5ms
* @param randomSequence true表示使用毫秒内的随机序列(超过范围则取余)
*/
public SnowflakeGenerationStrategy(long dataCenterId, long workerId, boolean clock, long timeOffset, boolean randomSequence) {
if (dataCenterId > MAX_DATA_CENTER_ID || dataCenterId < 0) {
throw new IllegalArgumentException("Data Center Id can't be greater than " +
MAX_DATA_CENTER_ID + " or less than 0");
}
if (workerId > MAX_WORKER_ID || workerId < 0) {
throw new IllegalArgumentException("Worker Id can't be greater than " +
MAX_WORKER_ID + " or less than 0");
}
this.workerId = workerId;
this.dataCenterId = dataCenterId;
this.clock = clock;
this.timeOffset = timeOffset;
this.randomSequence = randomSequence;
}
/**
* 获取ID
*
* @return long
*/
public synchronized Long nextId() {
long currentTimestamp = this.timeGen();
// 闰秒：如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过，这个时候应当抛出异常
if (currentTimestamp < lastTimestamp) {
// 校验时间偏移回拨量
long offset = lastTimestamp - currentTimestamp;
if (offset > timeOffset) {
throw new RuntimeException("Clock moved backwards, refusing to generate id for [" + offset + "ms]");
}
try {
// 时间回退timeOffset毫秒内，则允许等待2倍的偏移量后重新获取，解决小范围的时间回拨问题
this.wait(offset << 1);
} catch (Exception e) {
throw new RuntimeException(e);
}
// 再次获取
currentTimestamp = this.timeGen();
// 再次校验
if (currentTimestamp < lastTimestamp) {
throw new RuntimeException("Clock moved backwards, refusing to generate id for [" + offset + "ms]");
}
}
// 同一毫秒内序列直接自增
if (lastTimestamp == currentTimestamp) {
// randomSequence为true表示随机生成允许范围内的序列起始值并取余数,否则毫秒内起始值为0L开始自增
long tempSequence = sequence + 1;
if (randomSequence && tempSequence > SEQUENCE_MASK) {
tempSequence = tempSequence % SEQUENCE_MASK;
}
// 通过位与运算保证计算的结果范围始终是 0-4095
sequence = tempSequence & SEQUENCE_MASK;
if (sequence == 0) {
currentTimestamp = this.tilNextMillis(lastTimestamp);
}
} else {
// randomSequence为true表示随机生成允许范围内的序列起始值,否则毫秒内起始值为0L开始自增
sequence = randomSequence ? tlr.nextLong(SEQUENCE_MASK + 1) : 0L;
}
lastTimestamp = currentTimestamp;
long currentOffsetTime = currentTimestamp - START_TIME;
/*
* 1.左移运算是为了将数值移动到对应的段(41、5、5，12那段因为本来就在最右，因此不用左移)
* 2.然后对每个左移后的值(la、lb、lc、sequence)做位或运算，是为了把各个短的数据合并起来，合并成一个二进制数
* 3.最后转换成10进制，就是最终生成的id
*/
return (currentOffsetTime << TIMESTAMP_LEFT_SHIFT) |
// 数据中心位
(dataCenterId << DATA_CENTER_ID_SHIFT) |
// 工作ID位
(workerId << WORKER_ID_SHIFT) |
// 毫秒序列化位
sequence;
}
/**
* 保证返回的毫秒数在参数之后(阻塞到下一个毫秒，直到获得新的时间戳)——CAS
*
* @param lastTimestamp last timestamp
* @return next millis
*/
private long tilNextMillis(long lastTimestamp) {
long timestamp = this.timeGen();
while (timestamp <= lastTimestamp) {
// 如果发现时间回拨，则自动重新获取（可能会处于无限循环中）
timestamp = this.timeGen();
}
return timestamp;
}
/**
* 获得系统当前毫秒时间戳
*
* @return timestamp 毫秒时间戳
*/
private long timeGen() {
return clock ? SystemClockUtils.currentTimeMillis() : System.currentTimeMillis();
}
/**
* 用IP地址最后几个字节标示
*
* eg:192.168.1.30->30
*
* @return last IP
*/
private static byte getLastIPAddress() {
if (LAST_IP != 0) {
return LAST_IP;
}
try {
InetAddress inetAddress = InetAddress.getLocalHost();
byte[] addressByte = inetAddress.getAddress();
LAST_IP = addressByte[addressByte.length - 1];
} catch (Exception e) {
throw new RuntimeException("Unknown Host Exception", e);
}
return LAST_IP;
}
}