常見分布式ID

• 美團(tuán)Leaf：https://github.com/Meituan-Dianping/Leaf/

• 推特snowflake：https://github.com/twitter-archive/snowflake

• Redis

• 百度Uid-generator：https://github.com/baidu/uid-generator

snowflake簡(jiǎn)介

snowflake是Twitter開源的分布式ID生成算法，結(jié)果是一個(gè)long型的ID。

其核心思想是：使用41bit作為毫秒數(shù)（當(dāng)前時(shí)間截 - 開始時(shí)間截），10bit作為機(jī)器的ID（5個(gè)bit是數(shù)據(jù)中心，5個(gè)bit的機(jī)器ID），12bit作為毫秒內(nèi)的流水號(hào)（意味著每個(gè)節(jié)點(diǎn)在每毫秒可以產(chǎn)生 4096 個(gè) ID），最后還有一個(gè)符號(hào)位，永遠(yuǎn)是0。

這個(gè)算法單機(jī)每秒內(nèi)理論上最多可以生成1000*(2^12)，也就是409.6萬個(gè)ID

數(shù)據(jù)結(jié)構(gòu)

001.png

舉例

PHP 實(shí)現(xiàn)

代碼在yii框架中使用，配置如下

    'zookeeper'=>[
        'uri'=>'192.168.3.111:2181,192.168.3.112:2181,192.168.3.113:2181',
    ],
    'snow'=>[
        'rootPath'=>'/lock_snow',
        'keyPrefix'=>'/lock_',
        'info'=>'snow_lock'
    ]

如果需要在其他框架運(yùn)行，請(qǐng)?zhí)鎿Q相應(yīng)配置信息

<?php
namespace common\utils;

use common\utils\zookeeper\ZkUtil;
use yii\db\Exception;

class Snowflake
{
    const EPOCH = 1420041600000;    // 起始時(shí)間戳，毫秒

    const SEQUENCE_BITS = 12;   //序號(hào)部分12位
    const SEQUENCE_MAX = -1 ^ (-1 << self::SEQUENCE_BITS);  // 序號(hào)最大值

    const WORKER_BITS = 5; // 機(jī)器id部分5位
    const WORKER_MAX = -1 ^ (-1 << self::WORKER_BITS);  // 機(jī)器id最大數(shù)值

    const DATACENTER_BITS = 5;// 數(shù)據(jù)中心部分5位
    const DATACENTER_MAX = -1 ^ (-1 << self::DATACENTER_BITS);// 數(shù)據(jù)中心id最大值

    const TIME_SHIFT = self::WORKER_BITS + self::DATACENTER_BITS + self::SEQUENCE_BITS; // 時(shí)間戳部分左偏移量
    const DATACENTER_SHIFT = self::SEQUENCE_BITS + self::WORKER_BITS;
    const WORKER_SHIFT = self::SEQUENCE_BITS;   // 節(jié)點(diǎn)部分左偏移量

    protected $timestamp;   // 上次ID生成時(shí)間戳
    protected $workerId;    // 節(jié)點(diǎn)ID
    protected $dataCenterId;// 數(shù)據(jù)中心id
    protected $sequence;    // 序號(hào)

    public function __construct($workerId, $dataCenterId)
    {
        if ($workerId < 0 || $workerId > self::WORKER_MAX) {
            throw new Exception('節(jié)點(diǎn)ID超出范圍');
        }
        if($dataCenterId<0||$dataCenterId>self::DATACENTER_MAX){
            throw new Exception("數(shù)據(jù)中心id超出范圍");
        }
        $this->timestamp = 0;
        $this->workerId = $workerId;
        $this->dataCenterId = $dataCenterId;
    }

    public function getId()
    {
        $id = null;
        $params = \Yii::$app->params;//如果在其他框架運(yùn)行，請(qǐng)?zhí)鎿Q
        $conf['client_uri'] = $params['zookeeper']['uri'];;
        $root = $params['snow']['rootPath'];
        $lockKey = $params['snow']['keyPrefix'] . $this->workerId;
        // 開始獲取鎖
        ZkUtil::getInstance($conf, $root);
        if (!ZkUtil::tryClock($lockKey, $params['snow']['info'])) {
            throw new \Exception('獲取鎖失敗');
        }
        try {
            $now = $this->getMicroTime();
            if ($this->timestamp == $now) {
                $this->sequence++;
                if ($this->sequence > self::SEQUENCE_MAX) {
                    // 當(dāng)前毫秒內(nèi)生成的序號(hào)已經(jīng)超出最大范圍，等待下一毫秒重新生成
                    while ($now <= $this->timestamp) {
                        $now = $this->getMicroTime();
                    }
                }
            } else {
                $this->sequence = 0;
            }
            $this->timestamp = $now; // 更新ID生時(shí)間戳
            // 方法一、使用字符串拼接
//            $bin= decbin($now-self::EPOCH);
//            $bin = '0'.$bin;
//            $dataid=sprintf("%05s",decbin($this->dataCenterId));
//            $workid=sprintf("%05s",decbin($this->workerId));
//            $sequence = sprintf("%012s",decbin($this->sequence));
//            $id=$bin.$dataid.$workid.$sequence;
//            echo bindec($id);
            // 方法二、使用位運(yùn)算
            $id = (($now - self::EPOCH) << self::TIME_SHIFT) |($this->dataCenterId<<self::DATACENTER_SHIFT)| ($this->workerId << self::WORKER_SHIFT) | $this->sequence;
        } catch (\Exception $e) {
            echo $e->getMessage() . PHP_EOL;
        } finally {
            ZkUtil::releaseLock();
            return $id;
        }
    }

    private function getMicroTime()
    {
        $tArr = explode(" ", microtime());
        return (float) sprintf('%.0f',(floatval($tArr[1])+floatval($tArr[0]))*1000);
    }
}

ZkUtil：php編寫的zookeeper分布式鎖工具類

<?php

namespace common\utils\zookeeper;


class ZkUtil
{
    const debug = false;
    private static $_zk = null; // zk client
    private static $_node = null; // 當(dāng)前節(jié)點(diǎn)信息
    private static $_isNotifyed = null;
    private static $_root; // 根目錄
    private static $_acl = [ // 授權(quán)
        [
            'perms' => \Zookeeper::PERM_ALL,
            'scheme' => 'world',
            'id' => 'anyone',
        ]
    ];

    /**
     * 初始化鏈接
     * @param $conf
     * @param $root
     * @return \Zookeeper|null
     * @throws \Exception
     */
    public static function getInstance($conf, $root): ?\Zookeeper
    {
        if (self::$_zk !== null) return self::$_zk;
        $client = new \Zookeeper($conf['client_uri']);
        if (!$client) {
            throw new \Exception('connect zookeeper error');
        }

        self::$_root = $root;
        return self::$_zk = $client;
    }

    /**
     * 獲取鎖
     * @param $key
     * @param $value
     * @return false
     */
    public static function tryClock($key, $value): bool
    {
        try {
            self::createRoot($value);//構(gòu)建根節(jié)點(diǎn)
            self::createSub(self::$_root . $key, $value);//構(gòu)建子節(jié)點(diǎn)
            return self::getLock();//獲取鎖
        } catch (\Exception $e) {
            return false;
        }
    }

    /**
     * 釋放鎖
     * @return bool
     */
    public static function releaseLock(): bool
    {
        if (self::$_zk->delete(self::$_node)) {
            return true;
        } else {
            return false;
        }
    }

    /**
     * 創(chuàng)建根節(jié)點(diǎn)
     * @param $value
     * @return bool
     * @throws \Exception
     */
    public static function createRoot($value): bool
    {
        // 判讀根節(jié)點(diǎn)是否存在
        if (!self::$_zk->exists(self::$_root)) {
            // 創(chuàng)建根節(jié)點(diǎn) 創(chuàng)建成功返回節(jié)點(diǎn)名
            $result = self::$_zk->create(self::$_root, $value, self::$_acl);
            if (!$result) {
                throw new \Exception('create ' . self::$_root . '  fail');
            }
        }
        return true;
    }

    /**
     * 創(chuàng)建子節(jié)點(diǎn)
     * @param $path
     * @param $value
     * @return bool
     * @throws \Exception
     */
    public static function createSub($path, $value): bool
    {
        self::$_node = self::$_zk->create($path, $value, self::$_acl, \Zookeeper::EPHEMERAL | \Zookeeper::SEQUENCE);
        if (!self::$_node) {
            throw new \Exception('create -s -e ' . $path . ' fail');
        }
        if (self::debug){
            echo 'create - node：' . self::$_node . PHP_EOL;
        }
        return true;
    }

    /**
     * 獲取鎖
     * @return bool
     */
    public function getLock()
    {
        $beforeNode = self::checkNodeBefore();
        // 如果得到鎖返回
        if ($beforeNode === true) {
            return true;
        } else {
            self::$_isNotifyed = false;// 初始化狀態(tài)
            $result = self::$_zk->get($beforeNode, [ZkUtil::class, 'watcher']);

            while (!$result) {
                $res = self::checkNodeBefore();
                if ($res === true) {
                    return true;
                } else {
                    $result = self::$_zk->get($res, [ZkUtil::class, 'watcher']);
                }
            }
            while (!self::$_isNotifyed) {
                if(self::debug){
                    echo '.';
                }
                usleep(500000);//500ms
            }
            return true;
        }
    }

    public static function watcher($type, $state, $key)
    {
        if(self::debug){
            echo PHP_EOL . $key . ' notifyed ... ' . PHP_EOL;
        }
        self::$_isNotifyed = true;
        self::getLock();
    }

    /**
     * 檢查當(dāng)前節(jié)點(diǎn)是否可以得到鎖，如果不可以獲取它的上一個(gè)節(jié)點(diǎn)
     * @return bool
     */
    public function checkNodeBefore()
    {
        // 獲取所有子節(jié)點(diǎn)
        $nodes = self::$_zk->getChildren(self::$_root);
        // 對(duì)節(jié)點(diǎn)進(jìn)行排序
        sort($nodes);
        $root = self::$_root;
        // 節(jié)點(diǎn)全路徑拼接
        array_walk($nodes, function (&$val) use ($root) {
            $val = $root . '/' . $val;
        });
        // 判斷是否在首位
        if ($nodes[0] == self::$_node) {
            if(self::debug){
                echo 'get lock node ' . self::$_node . '------' . PHP_EOL;
            }
            return true;
        } else {
            // 找到當(dāng)前節(jié)點(diǎn)的上一個(gè)節(jié)點(diǎn)
            $index = array_search(self::$_node, $nodes);
            $before = $nodes[$index - 1];
            if(self::debug){
                echo 'before node ' . $before . '.....' . PHP_EOL;
            }
            return $before;
        }
    }
}

//function zkLock($resourceId)
//{
//    $conf['client_uri'] = '192.168.3.111:2181,192.168.3.112:2181,192.168.3.113:2181';
//    $root = '/lock_' . $resourceId;
//    $lockKey = '/lock_';
//    $value = 'server_info_1';
//    $client = ZkUtil::getInstance($conf, $root);
//    $re = ZkUtil::tryClock($lockKey, $value);
//    if ($re) {
//        echo 'get lock success' . PHP_EOL;
//    } else {
//        echo 'get lock fail' . PHP_EOL;
//        return false;
//    }
//    try {
//        action();
//    } catch (\Exception $e) {
//        echo $e->getMessage() . PHP_EOL;
//    } finally {
//        $re = ZkUtil::releaseLock();
//        if ($re) {
//            echo 'release lock success' . PHP_EOL;
//        } else {
//            echo 'release lock fail' . PHP_EOL;
//        }
//        return;
//    }
//}
//
//function action()
//{
//    $n = rand(1, 20);
//    switch ($n) {
//        case 1:
//            sleep(15);//模擬超時(shí)
//            break;
//        case 2:
//            throw new \Exception('system throw message...');//模擬中斷
//            break;
//        case 3:
//            die('system crashed...');//模擬程序崩潰
//            break;
//        default:
//            sleep(10);//正常處理
//            break;
//    }
//}
//
//zkLock(0);

java實(shí)現(xiàn)

/**
 * Twitter_Snowflake<br>
 * SnowFlake的結(jié)構(gòu)如下(每部分用-分開):<br>
 * 0 - 0000000000 0000000000 0000000000 0000000000 0 - 00000 - 00000 - 000000000000 <br>
 * 1位標(biāo)識(shí)，由于long基本類型在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 - 開始時(shí)間截)
 * 得到的值），這里的的開始時(shí)間截，一般是我們的id生成器開始使用的時(shí)間，由我們程序來指定的（如下下面程序IdWorker類的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ID左右。
 */
public class SnowflakeIdWorker {

    // ==============================Fields===========================================
    /** 開始時(shí)間截 (2015-01-01) */
    private final long twepoch = 1420041600000L;

    /** 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，說明系統(tǒng)時(shí)鐘回退過這個(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 < 1000; i++) {
            long id = idWorker.nextId();
            System.out.println(Long.toBinaryString(id));
            System.out.println(id);
        }
    }
}