可用的雪花版本有哪些？

常见的可用的雪花版本有两种：Twitter的Snowflake和美团的Leaf。

1. Twitter的Snowflake Snowflake是Twitter开源的一种分布式ID生成算法，它可以生成全局唯一、有序的64位ID。Snowflake的ID结构如下： | 1位符号位 | 41位时间戳 | 10位工作机器ID | 12位序列号 |

可以使用以下Java代码示例来使用Snowflake生成ID：

public class SnowflakeIdGenerator {
    private static final long EPOCH = 1609459200000L; // 2021-01-01 00:00:00
    private static final long WORKER_ID_BITS = 10L;
    private static final long SEQUENCE_BITS = 12L;
    private static final long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);
    private static final long MAX_SEQUENCE = ~(-1L << SEQUENCE_BITS);

    private final long workerId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;

    public SnowflakeIdGenerator(long workerId) {
        if (workerId < 0 || workerId > MAX_WORKER_ID) {
            throw new IllegalArgumentException("Worker ID is invalid");
        }
        this.workerId = workerId;
    }

    public synchronized long nextId() {
        long currentTimestamp = getCurrentTimestamp();
        if (currentTimestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards");
        }

        if (currentTimestamp == lastTimestamp) {
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0) {
                currentTimestamp = getNextTimestamp();
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = currentTimestamp;
        
        return ((currentTimestamp - EPOCH) << (WORKER_ID_BITS + SEQUENCE_BITS))
                | (workerId << SEQUENCE_BITS)
                | sequence;
    }

    private long getCurrentTimestamp() {
        return System.currentTimeMillis();
    }

    private long getNextTimestamp() {
        long timestamp = getCurrentTimestamp();
        while (timestamp <= lastTimestamp) {
            timestamp = getCurrentTimestamp();
        }
        return timestamp;
    }
}

// 使用示例
public class Main {
    public static void main(String[] args) {
        SnowflakeIdGenerator idGenerator = new SnowflakeIdGenerator(1);
        long id = idGenerator.nextId();
        System.out.println(id);
    }
}

2. 美团的Leaf Leaf是美团点评开源的一种分布式ID生成系统，它能够生成全局唯一、有序的64位ID。Leaf的ID结构如下： | 1位符号位 | 41位时间戳 | 10位工作机器ID | 12位序列号 |

可以使用以下Java代码示例来使用Leaf生成ID：

public class LeafIdGenerator {
    private static final long EPOCH = 1609459200000L; // 2021-01-01 00:00:00
    private static final long WORKER_ID_BITS = 10L;
    private static final long SEQUENCE_BITS = 12L;
    private static final long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);
    private static final long MAX_SEQUENCE = ~(-1L << SEQUENCE_BITS);

    private final long workerId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;

    public LeafIdGenerator(long workerId) {
        if (workerId < 0 || workerId > MAX_WORKER_ID) {
            throw new IllegalArgumentException("Worker ID is invalid");
        }
        this.workerId = workerId;
    }

    public synchronized long nextId() {
        long currentTimestamp = getCurrentTimestamp();
        if (currentTimestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards");
        }

        if (currentTimestamp == lastTimestamp) {
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0) {
                currentTimestamp = getNextTimestamp();
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = currentTimestamp;
        
        return ((currentTimestamp - EPOCH) << (WORKER_ID_BITS + SEQUENCE_BITS))
                | (workerId << SEQUENCE_BITS)
                | sequence;
    }

    private long getCurrentTimestamp() {
        return System.currentTimeMillis();
    }

    private long getNextTimestamp() {
        long timestamp = getCurrentTimestamp();
        while (timestamp <= lastTimestamp) {
            timestamp =