PHP版本的（snowflake）

snowflake算法好像是订单号的妈妈

生成订单号

在下订单时，我们需要为订单生成一个 唯一 的订单号，为了能够生成一个在高并发、集群环境下依然唯一的订单号，我们可以使用 twitter 提供的 snowflake 算法。

snowflake
snowflake 算法生成的订单号是由 64位（8个字节）二进制数来保存的，它的每一位的含义如下：

PHP 版本的 snowflake

由于 PHP 语言的特点，PHP中的数据用完就会销毁，下次再执行时又是全新的数据，这就导致在 PHP 中无效保存 上一次的数据 以及 持久存在的数字序列，为了解决这两个问题，我们可以使用 redis 来保存需要持久存在的数据。Snowflake 中有两个数据需要保存到 Redis ：上次生成的时间戳 和 序列ID。
所以修改之后的PHP版本的 Snowflake 为(以laravel框架实例)：

1、安装 redis 扩展

composer require predis/predis

2、在自定义php文件里添加 snowflake 类laravel自定义全局函数看这里
这里在 app/helpers.php 文件中添加

<?php
use Illuminate\Support\Facades\Redis;

...

// 生成唯一订单编号
function getOrderSn()
{
    $sf = new SnowFlake(0, 0);
    return $sf->generateID();
}

class SnowFlake
{
    /**
     * Offset from Unix Epoch
     * Unix Epoch : January 1 1970 00:00:00 GMT
     * Epoch Offset : January 1 2000 00:00:00 GMT
     */
    const EPOCH_OFFSET = 1483200000000;
    const SIGN_BITS = 1;
    const TIMESTAMP_BITS = 41;
    const DATACENTER_BITS = 5;
    const MACHINE_ID_BITS = 5;
    const SEQUENCE_BITS = 12;

    /**
     * @var mixed
     */
    protected $datacenter_id;

    /**
     * @var mixed
     */
    protected $machine_id;

    /**
     * @var null|int
     */
    // protected $lastTimestamp = null;   需要保存到 Redis

    /**
     * @var int
     */
    // protected $sequence = 1;   需要保存到 Redis

    protected $signLeftShift = self::TIMESTAMP_BITS + self::DATACENTER_BITS + self::MACHINE_ID_BITS + self::SEQUENCE_BITS;
    protected $timestampLeftShift = self::DATACENTER_BITS + self::MACHINE_ID_BITS + self::SEQUENCE_BITS;
    protected $dataCenterLeftShift = self::MACHINE_ID_BITS + self::SEQUENCE_BITS;
    protected $machineLeftShift = self::SEQUENCE_BITS;
    protected $maxSequenceId = -1 ^ (-1 << self::SEQUENCE_BITS);
    protected $maxMachineId = -1 ^ (-1 << self::MACHINE_ID_BITS);
    protected $maxDataCenterId = -1 ^ (-1 << self::DATACENTER_BITS);

    /**
     * Constructor to set required paremeters
     *
     * @param mixed $dataCenter_id Unique ID for datacenter (if multiple locations are used)
     * @param mixed $machine_id Unique ID for machine (if multiple machines are used)
     * @throws \Exception
     */
    public function __construct($dataCenter_id, $machine_id)
    {
        if ($dataCenter_id > $this->maxDataCenterId) {
            throw new \Exception('dataCenter id should between 0 and ' . $this->maxDataCenterId);
        }
        if ($machine_id > $this->maxMachineId) {
            throw new \Exception('machine id should between 0 and ' . $this->maxMachineId);
        }
        $this->datacenter_id = $dataCenter_id;
        $this->machine_id = $machine_id;
    }

    /**
     * Generate an unique ID based on SnowFlake
     * @return string
     * @throws \Exception
     */
    public function generateID()
    {
        $sign = 0; // default 0
        $timestamp = $this->getUnixTimestamp();

        $lastTimeStamp = Redis::get('shop:order:lastTimeStamp');

        if ($timestamp < $lastTimeStamp) {
            throw new \Exception('"Clock moved backwards!');
        }
        if ($timestamp == $lastTimeStamp) { //与上次时间戳相等，需要生成序列号
            $sequence = Redis::incr('shop:order:sequence');
            if ($sequence == $this->maxSequenceId) { //如果序列号超限，则需要重新获取时间
                $timestamp = $this->getUnixTimestamp();
                while ($timestamp <= $lastTimeStamp) {
                    $timestamp = $this->getUnixTimestamp();
                }
                Redis::set('shop:order:sequence', 1);
                $sequence = 1;
            }
        } else {
            Redis::set('shop:order:sequence', 1);
            $sequence = 1;
        }
        Redis::set('shop:order:lastTimeStamp', $timestamp);
        $time = (int)($timestamp - self::EPOCH_OFFSET);
        $id = ($sign << $this->signLeftShift) | ($time << $this->timestampLeftShift) | ($this->datacenter_id << $this->dataCenterLeftShift) | ($this->machine_id << $this->machineLeftShift) | $sequence;
        return (string)$id;
    }

    /**
     * Get UNIX timestamp in microseconds
     *
     * @return int  Timestamp in microseconds
     */
    private function getUnixTimestamp()
    {
        return floor(microtime(true) * 1000);
    }
}

添加之后就可以在项目中使用 getOrderSn 函数来生成订单号了：

    Route::get('testSN', function(){
    return getOrderSn();
});

参考自我的课程讲义