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推特演算法,分散式ID

package casclient_demo1.util;

import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.NetworkInterface;

/**
 * <p>名稱:IdWorker.java</p>
 * <p>描述:分散式自增長ID</p>
 * <pre>
 *     Twitter的 Snowflake JAVA實現方案
 * </pre>
 * 核心程式碼為其IdWorker這個類實現,其原理結構如下,我分別用一個0表示一位,用—分割開部分的作用:
 * 1||0---0000000000 0000000000 0000000000 0000000000 0 --- 00000 ---00000 ---000000000000
 * 在上面的字串中,第一位為未使用(實際上也可作為long的符號位),接下來的41位為毫秒級時間,
 * 然後5位datacenter標識位,5位機器ID(並不算識別符號,實際是為執行緒標識),
 * 然後12位該毫秒內的當前毫秒內的計數,加起來剛好64位,為一個Long型。
 * 這樣的好處是,整體上按照時間自增排序,並且整個分散式系統內不會產生ID碰撞(由datacenter和機器ID作區分),
 * 並且效率較高,經測試,snowflake每秒能夠產生26萬ID左右,完全滿足需要。
 * <p>
 * 64位ID (42(毫秒)+5(機器ID)+5(業務編碼)+12(重複累加))
 *
 * 
@author Polim */ public class IdWorker { // 時間起始標記點,作為基準,一般取系統的最近時間(一旦確定不能變動) private final static long twepoch = 1288834974657L; // 機器標識位數 private final static long workerIdBits = 5L; // 資料中心標識位數 private final static long datacenterIdBits = 5L; // 機器ID最大值 private final static
long maxWorkerId = -1L ^ (-1L << workerIdBits); // 資料中心ID最大值 private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits); // 毫秒內自增位 private final static long sequenceBits = 12L; // 機器ID偏左移12位 private final static long workerIdShift = sequenceBits; // 資料中心ID左移17位
private final static long datacenterIdShift = sequenceBits + workerIdBits; // 時間毫秒左移22位 private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits; private final static long sequenceMask = -1L ^ (-1L << sequenceBits); /* 上次生產id時間戳 */ private static long lastTimestamp = -1L; // 0,併發控制 private long sequence = 0L; private final long workerId; // 資料標識id部分 private final long datacenterId; public IdWorker(){ this.datacenterId = getDatacenterId(maxDatacenterId); this.workerId = getMaxWorkerId(datacenterId, maxWorkerId); } /** * @param workerId * 工作機器ID * @param datacenterId * 序列號 */ 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; } /** * 獲取下一個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) { // 當前毫秒內,則+1 sequence = (sequence + 1) & sequenceMask; if (sequence == 0) { // 當前毫秒內計數滿了,則等待下一秒 timestamp = tilNextMillis(lastTimestamp); } } else { sequence = 0L; } lastTimestamp = timestamp; // ID偏移組合生成最終的ID,並返回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> * 獲取 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 獲取16個低位 */ return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1); } /** * <p> * 資料標識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(); System.out.println(idWorker.nextId()); } }
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