SnowflakeIdWorker.php

<?php

class SnowflakeIdWorker
{
    // 开始时间戳（时间是2020-01-23 21:54:56，单位毫秒)
    // 此时间戳支持的时间约到2020+69
    private $twepoch = 1579816496000;

    // 机器id所占的位数
    const  WORKERID_BITS = 5;

    // 数据中心标识id所占的位数
    const  DATACENTERID_BITS = 5;

    // 序列在id中占的位数
    const SEQUENCE_BITS = 12;

    // 机器ID向左移12位
    private $workerIdShift = self::SEQUENCE_BITS;
 
    // 数据中心标识id向左移17位(12+5)
    private $datacenterIdShift = self::SEQUENCE_BITS + self::WORKERID_BITS;
 
    // 时间截向左移22位(5+5+12)
    private $timestampLeftShift = self::SEQUENCE_BITS + self::WORKERID_BITS + self::SEQUENCE_BITS;

    // 支持的最大机器id，结果是31
    // 通过移位算法计算出n位二进制数所能表示的最大十进制数
    private  $maxWorkerId = -1 ^ (-1 << self::WORKERID_BITS);

    // 支持的最大数据标识id，结果是31
    private  $maxDatacenterId = -1 ^ (-1 << self::DATACENTERID_BITS);

    // 生成序列的掩码，这里为4095 (0b111111111111=0xfff=4095)
    private $sequenceMask = -1 ^ (-1 << self::SEQUENCE_BITS);

    // 工作机器ID(0~31)
    private $workerId;
 
    // 数据中心ID(0~31)
    private $datacenterId;
  
    // 毫秒内序列(0~4095)
    // php非常驻内存运行模式下，sequence应该从第三方存储读写
    private $sequence = 0;

    // 上次生成ID的时间截
    // php非常驻内存运行模式下，lastTimestamp应该从第三方存储读写
    private $lastTimestamp = -1;

    public function __construct($workerId, $datacenterId)
    {
         if ($workerId > $this->maxWorkerId || $workerId < 0) {
            throw new IllegalArgumentException(sprintf("worker Id can't be greater than %d or less than 0", $maxWorkerId));
        }

        if ($datacenterId > $this->maxDatacenterId || $datacenterId < 0) {
            throw new IllegalArgumentException(sprintf("datacenter Id can't be greater than %d or less than 0", $maxDatacenterId));
        }

        $this->workerId = $workerId;
        $this->datacenterId = $datacenterId;
    }

    public function nextId()
    {
        $timestamp = $this->timeGen();
        // 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过这个时候应当抛出异常
        if ($timestamp < $this->lastTimestamp) {
            throw new RuntimeException(
                    sprintf("Clock moved backwards.  Refusing to generate id for %d milliseconds", $this->lastTimestamp - $timestamp));
        }

        // 如果是同一时间生成的，则进行毫秒内序列
        if ($this->lastTimestamp == $timestamp) {
            $this->sequence = ($this->sequence + 1) & $this->sequenceMask;
            // 毫秒内序列溢出
            if ($this->sequence == 0) {
                // 阻塞到下一个毫秒,获得新的时间戳
                $timestamp = $this->tilNextMillis($this->lastTimestamp);
            }
        } else { // 时间戳改变，毫秒内序列重置
            $this->sequence = 0;
        }

         // 记录上次生成ID的时间截
         $this->lastTimestamp = $timestamp;
 
         // 移位并通过或运算拼到一起组成64位的ID
         return (($timestamp - $this->twepoch) << $this->timestampLeftShift) //
                 | ($this->datacenterId << $this->datacenterIdShift) //
                 | ($this->workerId << $this->workerIdShift) //
                 | $this->sequence;
    }




    /**
     * 阻塞到下一个毫秒，直到获得新的时间戳
     * @param lastTimestamp 上次生成ID的时间截
     * @return 当前时间戳
     */
    protected function tilNextMillis($lastTimestamp)
    {
        $timestamp = $this->timeGen();
        while ($timestamp <= $lastTimestamp) {
            $timestamp = $this->timeGen();
        }
        return $timestamp;
    }

    protected  function timeGen()
    {
        return intval(microtime(true) * 1000);
    }
}

function  test()
{
    $idWorker = new SnowflakeIdWorker(0, 0);
    for ($i = 0; $i < 100000; $i++) {
        $id = $idWorker->nextId();
        printf("%d => %d\n", $i, ($id));
    }
}

test();