• redis不仅仅是单纯的缓存，它还有一些特殊的功能，在一些特殊场景上很好用。redis中key的原子自增incrby和判断key不存在再写入的setnx方法，可以有效的防止超发。
• 下面使用两个不同的方式来说明利用redis做商品购买库存数量限制。
• 业务场景很简单，就是限制抢购5个商品，模拟并发请求抢购商品，每抢购一次对应redis中的key值增加一次，通过判断限购的数量来限制抢购，抢购成功写入成功日志，失败写入失败的信息记录，通过记录的数量来判断是否超发。

文件index.php

<?php
require_once './myRedis.php';
require_once './function.php';
class sendAward{
 public $conf = [];
 const V1 = 'way1';//版本一
 const V2 = 'way2';//版本二
 const AMOUNTLIMIT = 5;//抢购数量限制
 const INCRAMOUNT = 1;//redis递增数量值
 
 //初始化调用对应方法执行商品发放
 public function __construct($conf,$type){
 $this->conf = $conf;
 if(empty($type))
 return '';
 if($type==self::V1){
 $this->way1(self::V1);
 }elseif($type==self::V2){
 $this->way2(self::V2);
 }else{
 return '';
 }
 }
 
 //抢购商品方式一
 protected function way1($v){
 $redis = new myRedis($this->conf); 
 $keyNmae = getKeyName($v);
 if(!$redis->exists($keyNmae)){
 $redis->set($keyNmae,0);
 }
 $currAmount = $redis->get($keyNmae);
 if(($currAmount+self::INCRAMOUNT)>self::AMOUNTLIMIT){
 writeLog("没有抢到商品",$v);
 return;
 }
 $redis->incrby($keyNmae,self::INCRAMOUNT);
 writeLog("抢到商品",$v);
 }
 
 //抢购商品方式二
 protected function way2($v){
 $redis = new myRedis($this->conf);
 $keyNmae = getKeyName($v);
 if(!$redis->exists($keyNmae)){
 $redis->setnx($keyNmae,0);
 }
 if($redis->incrby($keyNmae,self::INCRAMOUNT) > self::AMOUNTLIMIT){
 writeLog("没有抢到商品",$v);
 return;
 }
 writeLog("抢到商品",$v);
 }
 
}
//实例化调用对应执行方法
$type = isset($_GET['v'])?$_GET['v']:'way1';
$conf = [
 'host'=>'192.168.0.214','port'=>'6379',
 'auth'=>'test','db'=>2,
];
new sendAward($conf,$type);

文件myRedis.php

<?php

/**

* @desc 自定义redis操作类

* **/

class myRedis{

public $handler = NULL;

public function __construct($conf){

$this->handler = new Redis();

$this->handler->connect($conf['host'], $conf['port']); //连接Redis

//设置密码

if(isset($conf['auth'])){

$this->handler->auth($conf['auth']); //密码验证

}

//选择数据库

if(isset($conf['db'])){

$this->handler->select($conf['db']);//选择数据库2

}else{

$this->handler->select(0);//默认选择0库

}

}

//获取key的值

public function get($name){

return $this->handler->get($name);

}

//设置key的值

public function set($name,$value){

return $this->handler->set($name,$value);

}

//判断key是否存在

public function exists($key){

if($this->handler->exists($key)){

return true;

}

return false;

}

//当key不存在的设置key的值，存在则不设置

public function setnx($key,$value){

return $this->handler->setnx($key,$value);

}

//将key的数值增加指定数值

public function incrby($key,$value){

return $this->handler->incrBy($key,$value);

}

}

文件function.php

<?php
//获取商品key名称
function getKeyName($v)
{
 return "send_goods_".$v;
}
//日志写入方法
function writeLog($msg,$v)
{
 $log = $msg.PHP_EOL;
 file_put_contents("log/$v.log",$log,FILE_APPEND);
}

1.ab工具并发测试way1方法

[root@localhost oversend]# ab -c 100 -n 200 http://192.168.0.213:8083/index.php?v=way1
This is ApacheBench, Version 2.3 <$Revision: 655654 gt;
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/
Benchmarking 192.168.0.213 (be patient)
Completed 100 requests
Completed 200 requests
Finished 200 requests
Server Software: nginx
Server Hostname: 192.168.0.213
Server Port: 8083
Document Path: /index.php?v=way1
Document Length: 0 bytes
Concurrency Level: 100
Time taken for tests: 0.089 seconds
Complete requests: 200
Failed requests: 0
Write errors: 0
Total transferred: 30600 bytes
HTML transferred: 0 bytes
Requests per second: 2243.13 [#/sec] (mean)
Time per request: 44.581 [ms] (mean)
Time per request: 0.446 [ms] (mean, across all concurrent requests)
Transfer rate: 335.16 [Kbytes/sec] received
Connection Times (ms)
 min mean[+/-sd] median max
Connect: 0 6 2.2 5 17
Processing: 2 28 16.3 25 55
Waiting: 1 26 15.2 24 50
Total: 5 34 16.3 30 60
Percentage of the requests served within a certain time (ms)
 50% 30
 66% 35
 75% 54
 80% 56
 90% 57
 95% 60
 98% 60
 99% 60
 100% 60 (longest request)

v1方法日志分析

[root@localhost log]# less -N way1.log 
 1 抢到商品
 2 抢到商品
 3 抢到商品
 4 抢到商品
 5 抢到商品
 6 抢到商品
 7 没有抢到商品
 8 没有抢到商品
 9 没有抢到商品
 10 没有抢到商品
 11 没有抢到商品
 12 没有抢到商品

观察日志发现 抢到商品的记录有6条超过正常的5条，说明超发了

2.ab工具并发测试way2方法

[root@localhost oversend]# ab -c 100 -n 200 http://192.168.0.213:8083/index.php?v=way2
This is ApacheBench, Version 2.3 <$Revision: 655654 gt;
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/
Benchmarking 192.168.0.213 (be patient)
Completed 100 requests
Completed 200 requests
Finished 200 requests
Server Software: nginx
Server Hostname: 192.168.0.213
Server Port: 8083
Document Path: /index.php?v=way2
Document Length: 0 bytes
Concurrency Level: 100
Time taken for tests: 0.087 seconds
Complete requests: 200
Failed requests: 0
Write errors: 0
Total transferred: 31059 bytes
HTML transferred: 0 bytes
Requests per second: 2311.68 [#/sec] (mean)
Time per request: 43.259 [ms] (mean)
Time per request: 0.433 [ms] (mean, across all concurrent requests)
Transfer rate: 350.58 [Kbytes/sec] received
Connection Times (ms)
 min mean[+/-sd] median max
Connect: 0 6 5.4 5 13
Processing: 3 31 16.6 30 70
Waiting: 1 30 16.6 30 70
Total: 5 37 18.5 32 82
Percentage of the requests served within a certain time (ms)
 50% 32
 66% 41
 75% 45
 80% 50
 90% 68
 95% 80
 98% 81
 99% 82
 100% 82 (longest request)

v2方法日志分析

[root@localhost log]# less -N v2.log 
[root@localhost log]# less -N way2.log 
 1 抢到商品
 2 抢到商品
 3 抢到商品
 4 抢到商品
 5 没有抢到商品
 6 抢到商品
 7 没有抢到商品
 8 没有抢到商品
 9 没有抢到商品
 10 没有抢到商品

总结：观察日志可知抢到商品的日志记录是5条并没有超发，说明利用这种方式可以限制住库存的数量。之所以超发是因为方法一中通过加法来判断限制条件的同时，并发一大，就会越过这个判断条件出现会超发，redis的在这方面就体现优势了。