Twitter的分布式自增ID算法snowflake (Java版)

Posted 2020-11-17 jwcc

mport java.lang.management.ManagementFactory;

import java.net.InetAddress;

import java.net.NetworkInterface;

 

/**

* <p>名称：IdWorker.java</p> * <p>描述：分布式自增长ID</p> * <pre> * Twitter的 Snowflake　JAVA实现方案

* </pre> * 核心代码为其IdWorker这个类实现，其原理结构如下，我分别用一个0表示一位，用—分割开部分的作用：

* 1||0---0000000000 0000000000 0000000000 0000000000 0 --- 00000 ---00000 ---000000000000

* 在上面的字符串中，第一位为未使用（实际上也可作为long的符号位），接下来的41位为毫秒级时间，

* 然后5位datacenter标识位，5位机器ID（并不算标识符，实际是为线程标识），

* 然后12位该毫秒内的当前毫秒内的计数，加起来刚好64位，为一个Long型。

* 这样的好处是，整体上按照时间自增排序，并且整个分布式系统内不会产生ID碰撞（由datacenter和机器ID作区分），

* 并且效率较高，经测试，snowflake每秒能够产生26万ID左右，完全满足需要。

* <p> * 64位ID (42(毫秒)+5(机器ID)+5(业务编码)+12(重复累加))

*

* @author Polim

*/

public class IdWorker {

// 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）

private final static long twepoch = 1288834974657L;

// 机器标识位数

private final static long workerIdBits = 5L;

// 数据中心标识位数

private final static long datacenterIdBits = 5L;

// 机器ID最大值

private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);

// 数据中心ID最大值

private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);

// 毫秒内自增位

private final static long sequenceBits = 12L;

// 机器ID偏左移12位

private final static long workerIdShift = sequenceBits;

// 数据中心ID左移17位

private final static long datacenterIdShift = sequenceBits + workerIdBits;

// 时间毫秒左移22位

private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

 

private final static long sequenceMask = -1L ^ (-1L << sequenceBits);

/* 上次生产id时间戳 */

private static long lastTimestamp = -1L;

// 0，并发控制

private long sequence = 0L;

 

private final long workerId;

// 数据标识id部分

private final long datacenterId;

 

public IdWorker(){

this.datacenterId = getDatacenterId(maxDatacenterId);

this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);

}

/**

* @param workerId

* 工作机器ID

* @param datacenterId

* 序列号

*/

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;

}

/**

* 获取下一个ID

*

* @return

*/

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) {

// 当前毫秒内，则+1

sequence = (sequence + 1) & sequenceMask;

if (sequence == 0) {

// 当前毫秒内计数满了，则等待下一秒

timestamp = tilNextMillis(lastTimestamp);

}

} else {

sequence = 0L;

}

lastTimestamp = timestamp;

// ID偏移组合生成最终的ID，并返回ID

long nextId = ((timestamp - twepoch) << timestampLeftShift)

| (datacenterId << datacenterIdShift)

| (workerId << workerIdShift) | sequence;

 

return nextId;

}

 

private long tilNextMillis(final long lastTimestamp) {

long timestamp = this.timeGen();

while (timestamp <= lastTimestamp) {

timestamp = this.timeGen();

}

return timestamp;

}

 

private long timeGen() {

return System.currentTimeMillis();

}

 

/**

* <p> * 获取 maxWorkerId

* </p> */

protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {

StringBuffer mpid = new StringBuffer();

mpid.append(datacenterId);

String name = ManagementFactory.getRuntimeMXBean().getName();

if (!name.isEmpty()) {

/*

* GET jvmPid

*/

mpid.append(name.split("@")[0]);

}

/*

* MAC + PID 的 hashcode 获取16个低位 */

return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);

}

 

/**

* <p> * 数据标识id部分

* </p> */

protected static long getDatacenterId(long maxDatacenterId) {

long id = 0L;

try {

InetAddress ip = InetAddress.getLocalHost();

NetworkInterface network = NetworkInterface.getByInetAddress(ip);

if (network == null) {

id = 1L;

} else {

byte[] mac = network.getHardwareAddress();

id = ((0x000000FF & (long) mac[mac.length - 1])

| (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;

id = id % (maxDatacenterId + 1);

}

} catch (Exception e) {

System.out.println(" getDatacenterId: " + e.getMessage());

}

return id;

}

 

public static void main(String[] args) {

IdWorker idWorker = new IdWorker(31,31);

System.out.println("idWorker="+idWorker.nextId());

IdWorker id = new IdWorker();

System.out.println("id="+id.nextId());

System.out.println(id.datacenterId);

System.out.println(id.workerId);

}

}