PHP uses redis lock to limit concurrent access class example

This article introduces the use of redis locks in PHP to limit concurrent access classes, and introduces the concurrent access restriction methods in detail.

1. Concurrent access restriction issues

For some scenarios where concurrent access by the same user needs to be restricted, if the user makes multiple concurrent requests, and the server process has no locking restrictions , the user can successfully request multiple times.

For example, when redeeming coupons, if the user submits the redemption code concurrently at the same time, the user can use the same redemption code to redeem multiple coupons at the same time without locking restrictions.

The pseudo code is as follows:

if A (Can be redeemed)
B (Execute redemption)
C (Updated to have been redeemed)
D (End)

If users submit redemption codes concurrently, they can all be judged as redeemable (A), because one must execute redemption (B) before it will be updated to redeemed Collar (C). Therefore, if the user makes multiple requests before one is updated as redeemed, these requests can be executed successfully.

2. Concurrent access restriction method

Using file locks can achieve concurrent access restrictions, but for a distributed architecture environment, using file locks cannot guarantee concurrent access restrictions on multiple servers.

Redis is an open source log-type Key-Value database written in ANSI C language, supports network, can be memory-based and persistent, and provides APIs in multiple languages.

This article will use its setnx method to implement the distributed lock function. setnx is Set it N**ot eX**ists.

When the key value does not exist, the insertion is successful (the lock is acquired successfully). If the key value already exists, the insertion fails (the lock acquisition fails)

RedisLock.class.PHP

<?php
/**
 * Redis锁操作类
 * Date:  2016-06-30
 * Author: fdipzone
 * Ver:  1.0
 *
 * Func:
 * public lock  获取锁
 * public unlock 释放锁
 * private connect 连接
 */
class RedisLock { // class start
 
  private $_config;
  private $_redis;
 
  /**
   * 初始化
   * @param Array $config redis连接设定
   */
  public function __construct($config=array()){
    $this->_config = $config;
    $this->_redis = $this->connect();
  }
 
  /**
   * 获取锁
   * @param String $key  锁标识
   * @param Int   $expire 锁过期时间
   * @return Boolean
   */
  public function lock($key, $expire=5){
    $is_lock = $this->_redis->setnx($key, time()+$expire);
 
    // 不能获取锁
    if(!$is_lock){
 
      // 判断锁是否过期
      $lock_time = $this->_redis->get($key);
 
      // 锁已过期，删除锁，重新获取
      if(time()>$lock_time){
        $this->unlock($key);
        $is_lock = $this->_redis->setnx($key, time()+$expire);
      }
    }
 
    return $is_lock? true : false;
  }
 
  /**
   * 释放锁
   * @param String $key 锁标识
   * @return Boolean
   */
  public function unlock($key){
    return $this->_redis->del($key);
  }
 
  /**
   * 创建redis连接
   * @return Link
   */
  private function connect(){
    try{
      $redis = new Redis();
      $redis->connect($this->_config[&#39;host&#39;],$this->_config[&#39;port&#39;],$this->_config[&#39;timeout&#39;],$this->_config[&#39;reserved&#39;],$this->_config[&#39;retry_interval&#39;]);
      if(empty($this->_config[&#39;auth&#39;])){
        $redis->auth($this->_config[&#39;auth&#39;]);
      }
      $redis->select($this->_config[&#39;index&#39;]);
    }catch(RedisException $e){
      throw new Exception($e->getMessage());
      return false;
    }
    return $redis;
  }
 
} // class end
 
?>

demo.php

<?php
require &#39;RedisLock.class.php&#39;;
 
$config = array(
  &#39;host&#39; => &#39;localhost&#39;,
  &#39;port&#39; => 6379,
  &#39;index&#39; => 0,
  &#39;auth&#39; => &#39;&#39;,
  &#39;timeout&#39; => 1,
  &#39;reserved&#39; => NULL,
  &#39;retry_interval&#39; => 100,
);
 
// 创建redislock对象
$oRedisLock = new RedisLock($config);
 
// 定义锁标识
$key = &#39;mylock&#39;;
 
// 获取锁
$is_lock = $oRedisLock->lock($key, 10);
 
if($is_lock){
  echo &#39;get lock success<br>&#39;;
  echo &#39;do sth..<br>&#39;;
  sleep(5);
  echo &#39;success<br>&#39;;
  $oRedisLock->unlock($key);
 
// 获取锁失败
}else{
  echo &#39;request too frequently<br>&#39;;
}
 
?>

Test method:

Open two different browsers and access demo.php in A and B at the same time

If you access it first, you will get the lock

Output

get lock success
do sth..
success

If another one fails to obtain the lock, request too frequently will be output

Ensure that only one access is valid at the same time , effectively limiting concurrent access.

In order to avoid deadlock caused by sudden system errors, an expiration time is added when acquiring the lock. If the expiration time has passed, the lock will be released even in the locked state to avoid problems caused by deadlock.

For more PHP related articles on using redis lock to limit concurrent access class examples, please pay attention to the PHP Chinese website!