关于雪花算法全是偶数的问题处理

1. 问题描述 生成的id全是偶数的
2. 问题发现 由于跨毫秒后,最后的sequence累加就会清零,导入末位为偶数。如果id生成不频繁,则生成的就是全是偶数
3. 解决 【关于雪花算法全是偶数的问题处理】主要的根本就在跨毫秒清零,如果在跨毫秒时候sequence不清零,实际上每次生成id时,时间毫秒在增加,sequence也在增加,也是不会重复的。所以,索性去掉这一块
同时由于sequence = (sequence + 1) & MAX_SEQUENCE; sequence累加到最大值后,下一次依然是0,所以只保留这句话就行了。

完整代码:

class Snowflake { /** * 起始的时间戳 */ private final static long START_STMP = 1480166465631L; /** * 每一部分占用的位数 */ private final static long SEQUENCE_BIT = 12; // 序列号占用的位数 private final static long MACHINE_BIT = 5; // 机器标识占用的位数 private final static long DATACENTER_BIT = 5; // 数据中心占用的位数 /** * 每一部分的最大值 */ private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT); private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT); private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT); /** * 每一部分向左的位移 */ private final static long MACHINE_LEFT = SEQUENCE_BIT; private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT; private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT; private long datacenterId; // 数据中心 private long machineId; // 机器标识 private long sequence = 0L; // 序列号 private long lastStmp = -1L; // 上一次时间戳 public Snowflake(long datacenterId, long machineId) { if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) { throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0"); } if (machineId > MAX_MACHINE_NUM || machineId < 0) { throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0"); } this.datacenterId = datacenterId; this.machineId = machineId; } /** * 产生下一个ID * * @return */ public synchronized long createId() { long currStmp = getNewstmp(); if (currStmp < lastStmp) { throw new RuntimeException("Clock moved backwards.Refusing to generate id"); }sequence = (sequence + 1) & MAX_SEQUENCE; //下方的原代码,全部注释,值保留上面一行,解决跨毫秒全为偶数问题 //if (currStmp == lastStmp) { ////相同毫秒内,序列号自增 //sequence = (sequence + 1) & MAX_SEQUENCE; ////同一毫秒的序列数已经达到最大 //if (sequence == 0L) { //currStmp = getNextMill(); //} //} else { ////不同毫秒内,序列号置为0 //sequence = 0L; //}lastStmp = currStmp; return (currStmp - START_STMP) << TIMESTMP_LEFT // 时间戳部分 | datacenterId << DATACENTER_LEFT // 数据中心部分 | machineId << MACHINE_LEFT // 机器标识部分 | sequence; // 序列号部分 } private long getNextMill() { long mill = getNewstmp(); while (mill <= lastStmp) { mill = getNewstmp(); } return mill; } private long getNewstmp() { return System.currentTimeMillis(); } public static void main(String[] args) { Snowflake snowFlake = new Snowflake(2, 3); long start = System.currentTimeMillis(); for (int i = 0; i < 1000000; i++) { System.out.println(snowFlake.createId()); }System.out.println(System.currentTimeMillis() - start); } }


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