twitter snowflake java版

最近要用到这个, 仿造twitter的官方scala源码做了一个java版本. 因为是照着官方源码逐字翻译的, 所以和网上的其他版本大同小异, 并不是抄来的. 去掉了自定义sequence初始值的功能, 因为个人觉得用处不大; 并且出于性能考虑, 对几行代码做了inline处理, 所以代码比官方代码短一点. 

源码:

/**
 * Snowflake java version.
 * From scala version at https://github.com/twitter/snowflake/releases/tag/snowflake-2010.
 *
 * Created by [email protected] on 2017/3/22.
 */
public class IdWorker implements IdGenerator {
    /*2017-01-01 00:00:00*/
    private final long twepoch = 1483200000000L;

    private final long workerIdBits = 5L;
    private final long datacenterIdBits = 5L;
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private final long sequenceBits = 12L;

    private final long workerIdShift = sequenceBits;
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);

    private long workerId;
    private long datacenterId;
    private long sequence = 0L;

    private long lastTimestamp = -1L;

    public IdWorker(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 long getId() {
        return nextId();
    }

    public synchronized long nextId() {
        long timestamp = System.currentTimeMillis();
        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) << timestampLeftShift) |
                (datacenterId << datacenterIdShift) |
                (workerId << workerIdShift) |
                sequence;
    }

    private long tilNextMillis(long lastTimestamp) {
        long timestamp = System.currentTimeMillis();
        while (timestamp <= lastTimestamp) {
            timestamp = System.currentTimeMillis();
        }
        return timestamp;
    }
}

测试:

import org.testng.annotations.Test;

/**
 * Test IdWorker
 *
 * Created by [email protected] on 2017/3/22.
 */
public class IdWorkerTest {
    @Test
    public void testGetId() {
        IdWorker idGenerator = new IdWorker(0, 0, 0);
        long start = System.currentTimeMillis();
        for (int i = 0; i < 1000000; i++) {
            System.out.println(idGenerator.getId());
        }
        System.out.println("Elapsed:" + (System.currentTimeMillis() - start));
    }
}

经测试, 在i3 CPU和"-Xmx64M"的环境下, 每毫秒生成260个左右. 幸好不是250.

Read more: twitter snowflake生成流水号的系统时间后调问题