【Spring Cloud系列】 雪花算法原理及实现

雪花算法(Snowflake algorithm)是一种生成全局唯一ID的算法，它能够保证在分布式系统中每个节点每秒钟生成不重复的ID。

雪花算法的核心思想是：使用64位的整数来生成ID，其中：

1. 1位不用，因为二进制表示的时候最高位是符号位，1表示负数，所以正数的最高位是0，可以用于表示。
2. 41位时间戳，单位是毫秒。可以容纳约69年的时间。
3. 10位节点ID，可以容纳1024个节点。
4. 12位序列号，可以在同毫秒内生成4096个ID。

以下是一个简单的Java实现：

public class SnowflakeIdGenerator {
    private final long twepoch = 1577808548000L; // 假设自己的系统起始时间（毫秒）
    private final long workerIdBits = 10L; // 节点ID的位数
    private final long datacenterIdBits = 5L; // 数据中心ID的位数
    private final long sequenceBits = 12L; // 序列号的位数
 
    private final long workerIdShift = sequenceBits;
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
 
    private final long sequenceMask = -1L ^ (-1L << (int)sequenceBits);
    private final long workerId;
    private final long datacenterId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;
 
    public SnowflakeIdGenerator(long workerId, long datacenterId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException("workerId can't be greater than %d or less than 0");
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than %d or less than 0");
        }
        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 (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0;
        }
 
        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) {