snowflake算法由twitter公司出品,原始版本是scala版,用于生成分布式ID,结构图:

算法描述:

  • 最高位是符号位,始终为0,不可用。
  • 41位的时间序列,精确到毫秒级,41位的长度可以使用69年。时间位还有一个很重要的作用是可以根据时间进行排序。
  • 10位的机器标识,10位的长度最多支持部署1024个节点
  • 12位的计数序列号,序列号即一系列的自增id,可以支持同一节点同一毫秒生成多个ID序号,12位的计数序列号支持每个节点每毫秒产生4096个ID序号
    package com.zhi.idworker.lang;
    
    /**
     * 分布式雪花ID算法
     *
     * @author zhi
     * @since 2019年5月14日16:51:06
     *
     */
    public class SnowFlake {
        /**
         * 起始的时间戳
         */
        private final static long twepoch = 1557825652094L;
    
        /**
         * 每一部分占用的位数
         */
        private final static long workerIdBits = 5L;
        private final static long datacenterIdBits = 5L;
        private final static long sequenceBits = 12L;
    
        /**
         * 每一部分的最大值
         */
        private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
        private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
        private final static long maxSequence = -1L ^ (-1L << sequenceBits);
    
        /**
         * 每一部分向左的位移
         */
        private final static long workerIdShift = sequenceBits;
        private final static long datacenterIdShift = sequenceBits + workerIdBits;
        private final static long timestampShift = sequenceBits + workerIdBits + datacenterIdBits;
    
        private long datacenterId; // 数据中心ID
        private long workerId; // 机器ID
        private long sequence = 0L; // 序列号
        private long lastTimestamp = -1L; // 上一次时间戳
    
        public SnowFlake(long workerId, long datacenterId) {
            if (workerId > maxWorkerId || workerId < 0) {
                throw new IllegalArgumentException(
                        String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
            }
            if (datacenterId > maxDatacenterId || datacenterId < 0) {
                throw new IllegalArgumentException(
                        String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
            }
            this.workerId = workerId;
            this.datacenterId = datacenterId;
        }
    
        public synchronized long nextId() {
            long timestamp = timeGen();
            if (timestamp < lastTimestamp) {
                throw new RuntimeException(String.format(
                        "Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
            }
            if (timestamp == lastTimestamp) {
                sequence = (sequence + 1) & maxSequence;
                if (sequence == 0L) {
                    timestamp = tilNextMillis();
                }
            } else {
                sequence = 0L;
            }
            lastTimestamp = timestamp;
    
            return (timestamp - twepoch) << timestampShift // 时间戳部分
                    | datacenterId << datacenterIdShift // 数据中心部分
                    | workerId << workerIdShift // 机器标识部分
                    | sequence; // 序列号部分
        }
    
        private long tilNextMillis() {
            long timestamp = timeGen();
            while (timestamp <= lastTimestamp) {
                timestamp = timeGen();
            }
            return timestamp;
        }
    
        private long timeGen() {
            return System.currentTimeMillis();
        }
    }
    View Code

Java实现:

package com.zhi.idworker;

/**
 * 分布式雪花ID算法
 *
 * @author zhi
 * @since 2019年5月14日16:51:06
 *
 */
public class SnowFlake {
    /**
     * 起始的时间戳
     */
    private final static long twepoch = 1557825652094L;

    /**
     * 每一部分占用的位数
     */
    private final static long workerIdBits = 5L;
    private final static long datacenterIdBits = 5L;
    private final static long sequenceBits = 12L;

    /**
     * 每一部分的最大值
     */
    private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private final static long maxSequence = -1L ^ (-1L << sequenceBits);

    /**
     * 每一部分向左的位移
     */
    private final static long workerIdShift = sequenceBits;
    private final static long datacenterIdShift = sequenceBits + workerIdBits;
    private final static long timestampShift = sequenceBits + workerIdBits + datacenterIdBits;

    private long datacenterId; // 数据中心ID
    private long workerId; // 机器ID
    private long sequence = 0L; // 序列号
    private long lastTimestamp = -1L; // 上一次时间戳

    public SnowFlake(long workerId, long datacenterId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(
                    String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(
                    String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }

    public synchronized long nextId() {
        long timestamp = timeGen();
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format(
                    "Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }
        if (timestamp == lastTimestamp) {
            sequence = (sequence + 1) & maxSequence;
            if (sequence == 0L) {
                timestamp = tilNextMillis();
            }
        } else {
            sequence = 0L;
        }
        lastTimestamp = timestamp;

        return (timestamp - twepoch) << timestampShift // 时间戳部分
                | datacenterId << datacenterIdShift // 数据中心部分
                | workerId << workerIdShift // 机器标识部分
                | sequence; // 序列号部分
    }

    private long tilNextMillis() {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    private long timeGen() {
        return System.currentTimeMillis();
    }
}
View Code
01-07 19:42