mysql實(shí)現(xiàn)雪花算法的案例分析

package com.yl.common;
/**
 * Twitter_Snowflake<br>
 * SnowFlake的結(jié)構(gòu)如下(每部分用-分開(kāi)):<br>
 * 0 - 0000000000 0000000000 0000000000 0000000000 0 - 00000 - 00000 - 000000000000 <br>
 * 1位標(biāo)識(shí)，由于long基本類(lèi)型在Java中是帶符號(hào)的，最高位是符號(hào)位，正數(shù)是0，負(fù)數(shù)是1，所以id一般是正數(shù)，最高位是0<br>
 * 41位時(shí)間截(毫秒級(jí))，注意，41位時(shí)間截不是存儲(chǔ)當(dāng)前時(shí)間的時(shí)間截，而是存儲(chǔ)時(shí)間截的差值（當(dāng)前時(shí)間截 - 開(kāi)始時(shí)間截)
 * 得到的值），這里的的開(kāi)始時(shí)間截，一般是我們的id生成器開(kāi)始使用的時(shí)間，由我們程序來(lái)指定的（如下下面程序IdWorker類(lèi)的startTime屬性）。41位的時(shí)間截，可以使用69年，年T = (1L << 41) / (1000L * 60 * 60 * 24 * 365) = 69<br>
 * 10位的數(shù)據(jù)機(jī)器位，可以部署在1024個(gè)節(jié)點(diǎn)，包括5位datacenterId和5位workerId<br>
 * 12位序列，毫秒內(nèi)的計(jì)數(shù)，12位的計(jì)數(shù)順序號(hào)支持每個(gè)節(jié)點(diǎn)每毫秒(同一機(jī)器，同一時(shí)間截)產(chǎn)生4096個(gè)ID序號(hào)<br>
 * 加起來(lái)剛好64位，為一個(gè)Long型。<br>
 * SnowFlake的優(yōu)點(diǎn)是，整體上按照時(shí)間自增排序，并且整個(gè)分布式系統(tǒng)內(nèi)不會(huì)產(chǎn)生ID碰撞(由數(shù)據(jù)中心ID和機(jī)器ID作區(qū)分)，并且效率較高，經(jīng)測(cè)試，SnowFlake每秒能夠產(chǎn)生26萬(wàn)ID左右。
 */
public class SnowflakeIdWorker {

 // ==============================Fields===========================================
 /** 開(kāi)始時(shí)間截 (2020-01-01) */
 private final long twepoch = 1577808000000L;

 /** 機(jī)器id所占的位數(shù) */
 private final long workerIdBits = 5L;

 /** 數(shù)據(jù)標(biāo)識(shí)id所占的位數(shù) */
 private final long datacenterIdBits = 5L;

 /** 支持的最大機(jī)器id，結(jié)果是31 (這個(gè)移位算法可以很快的計(jì)算出幾位二進(jìn)制數(shù)所能表示的最大十進(jìn)制數(shù)) */
 private final long maxWorkerId = -1L ^ (-1L << workerIdBits);

 /** 支持的最大數(shù)據(jù)標(biāo)識(shí)id，結(jié)果是31 */
 private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);

 /** 序列在id中占的位數(shù) */
 private final long sequenceBits = 12L;

 /** 機(jī)器ID向左移12位 */
 private final long workerIdShift = sequenceBits;

 /** 數(shù)據(jù)標(biāo)識(shí)id向左移17位(12+5) */
 private final long datacenterIdShift = sequenceBits + workerIdBits;

 /** 時(shí)間截向左移22位(5+5+12) */
 private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

 /** 生成序列的掩碼，這里為4095 (0b111111111111=0xfff=4095) */
 private final long sequenceMask = -1L ^ (-1L << sequenceBits);

 /** 工作機(jī)器ID(0~31) */
 private long workerId;

 /** 數(shù)據(jù)中心ID(0~31) */
 private long datacenterId;

 /** 毫秒內(nèi)序列(0~4095) */
 private long sequence = 0L;

 /** 上次生成ID的時(shí)間截 */
 private long lastTimestamp = -1L;

 //==============================Constructors=====================================
 /**
  * 構(gòu)造函數(shù)
  * @param workerId 工作ID (0~31)
  * @param datacenterId 數(shù)據(jù)中心ID (0~31)
  */
 public SnowflakeIdWorker(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;
 }

 // ==============================Methods==========================================
 /**
  * 獲得下一個(gè)ID (該方法是線程安全的)
  * @return SnowflakeId
  */
 public synchronized long nextId() {
  long timestamp = timeGen();

  //如果當(dāng)前時(shí)間小于上一次ID生成的時(shí)間戳，說(shuō)明系統(tǒng)時(shí)鐘回退過(guò)這個(gè)時(shí)候應(yīng)當(dāng)拋出異常
  if (timestamp < lastTimestamp) {
   throw new RuntimeException(
     String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
  }

  //如果是同一時(shí)間生成的，則進(jìn)行毫秒內(nèi)序列
  if (lastTimestamp == timestamp) {
   sequence = (sequence + 1) & sequenceMask;
   //毫秒內(nèi)序列溢出
   if (sequence == 0) {
    //阻塞到下一個(gè)毫秒,獲得新的時(shí)間戳
    timestamp = tilNextMillis(lastTimestamp);
   }
  }
  //時(shí)間戳改變，毫秒內(nèi)序列重置
  else {
   sequence = 0L;
  }

  //上次生成ID的時(shí)間截
  lastTimestamp = timestamp;

  //移位并通過(guò)或運(yùn)算拼到一起組成64位的ID
  return ((timestamp - twepoch) << timestampLeftShift) //
    | (datacenterId << datacenterIdShift) //
    | (workerId << workerIdShift) //
    | sequence;
 }

 /**
  * 阻塞到下一個(gè)毫秒，直到獲得新的時(shí)間戳
  * @param lastTimestamp 上次生成ID的時(shí)間截
  * @return 當(dāng)前時(shí)間戳
  */
 protected long tilNextMillis(long lastTimestamp) {
  long timestamp = timeGen();
  while (timestamp <= lastTimestamp) {
   timestamp = timeGen();
  }
  return timestamp;
 }

 /**
  * 返回以毫秒為單位的當(dāng)前時(shí)間
  * @return 當(dāng)前時(shí)間(毫秒)
  */
 protected long timeGen() {
  return System.currentTimeMillis();
 }

 //==============================Test=============================================
 /** 測(cè)試 */
 public static void main(String[] args) {
  SnowflakeIdWorker idWorker = new SnowflakeIdWorker(0, 0);
  
  for (int i = 0; i < 100; i++) {
   long id = idWorker.nextId();
   System.out.println(id);
  }
 }
}

/**
 * <p>名稱：IdWorker.java</p>
 * <p>描述：分布式自增長(zhǎng)ID</p>
 * <pre>
 *   Twitter的 Snowflake　JAVA實(shí)現(xiàn)方案
 * </pre>
 * 核心代碼為其IdWorker這個(gè)類(lèi)實(shí)現(xiàn)，其原理結(jié)構(gòu)如下，我分別用一個(gè)0表示一位，用—分割開(kāi)部分的作用：
 * 1||0---0000000000 0000000000 0000000000 0000000000 0 --- 00000 ---00000 ---000000000000
 * 在上面的字符串中，第一位為未使用（實(shí)際上也可作為long的符號(hào)位），接下來(lái)的41位為毫秒級(jí)時(shí)間，
 * 然后5位datacenter標(biāo)識(shí)位，5位機(jī)器ID（并不算標(biāo)識(shí)符，實(shí)際是為線程標(biāo)識(shí)），
 * 然后12位該毫秒內(nèi)的當(dāng)前毫秒內(nèi)的計(jì)數(shù)，加起來(lái)剛好64位，為一個(gè)Long型。
 * 這樣的好處是，整體上按照時(shí)間自增排序，并且整個(gè)分布式系統(tǒng)內(nèi)不會(huì)產(chǎn)生ID碰撞（由datacenter和機(jī)器ID作區(qū)分），
 * 并且效率較高，經(jīng)測(cè)試，snowflake每秒能夠產(chǎn)生26萬(wàn)ID左右，完全滿足需要。
 * <p>
 * 64位ID (42(毫秒)+5(機(jī)器ID)+5(業(yè)務(wù)編碼)+12(重復(fù)累加))
 *
 * @author Polim
 */
public class IdWorker {
  // 時(shí)間起始標(biāo)記點(diǎn)，作為基準(zhǔn)，一般取系統(tǒng)的最近時(shí)間（一旦確定不能變動(dòng)）
  private final static long twepoch = 1288834974657L;
  // 機(jī)器標(biāo)識(shí)位數(shù)
  private final static long workerIdBits = 5L;
  // 數(shù)據(jù)中心標(biāo)識(shí)位數(shù)
  private final static long datacenterIdBits = 5L;
  // 機(jī)器ID最大值
  private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
  // 數(shù)據(jù)中心ID最大值
  private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
  // 毫秒內(nèi)自增位
  private final static long sequenceBits = 12L;
  // 機(jī)器ID偏左移12位
  private final static long workerIdShift = sequenceBits;
  // 數(shù)據(jù)中心ID左移17位
  private final static long datacenterIdShift = sequenceBits + workerIdBits;
  // 時(shí)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(chǎn)id時(shí)間戳 */
  private static long lastTimestamp = -1L;
  // 0，并發(fā)控制
  private long sequence = 0L;

  private final long workerId;
  // 數(shù)據(jù)標(biāo)識(shí)id部分
  private final long datacenterId;

  public IdWorker(){
    this.datacenterId = getDatacenterId(maxDatacenterId);
    this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);
  }
  /**
   * @param workerId
   *      工作機(jī)器ID
   * @param datacenterId
   *      序列號(hào)
   */
  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(gè)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(dāng)前毫秒內(nèi)，則+1
      sequence = (sequence + 1) & sequenceMask;
      if (sequence == 0) {
        // 當(dāng)前毫秒內(nèi)計(jì)數(shù)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，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>
   * 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(gè)低位
    */
    return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
  }

  /**
   * <p>
   * 數(shù)據(jù)標(biāo)識(shí)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;
  }


}