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php如何将并发加锁的示例代码

黄舟

Lepaskan： 2023-03-14 09:48:01

asal

2386 orang telah melayarinya

CleverCode在工作项目中，会遇到一些php并发访问去修改一个数据问题，如果这个数据不加锁，就会造成数据的错误。下面CleverCode将分析一个财务支付锁的问题。

1 没有应用锁机制

1.1 财务支付简化版本代码

<?php

/** 
 * pay.php 
 * 
 * 支付没有应用锁
 * 
 * Copy right (c) 2016 http://blog.csdn.net/CleverCode 
 * 
 * modification history: 
 * -------------------- 
 * 2016/9/10, by CleverCode, Create 
 * 
 */  

//用户支付
function pay($userId,$money)
{
    
    if(false == is_int($userId) || false == is_int($money))
    {
        return false;
    }  
    
    //取出总额
    $total = getUserLeftMoney($userId);
    
    //花费大于剩余
    if($money > $total)
    {
        return false;    
    }
    
    //余额
    $left = $total - $money;
    
    //更新余额
    return setUserLeftMoney($userId,$left);

}

//取出用户的余额
function getUserLeftMoney($userId)
{
    if(false == is_int($userId))
    {
        return 0;
    }
    $sql = "select account form user_account where userid = ${userId}";
    
    //$mysql = new mysql();//mysql数据库
    return $mysql->query($sql);
}

//更新用户余额
function setUserLeftMoney($userId,$money)
{
    if(false == is_int($userId) || false == is_int($money))
    {
        return false;
    }        
    
    $sql = "update user_account set account = ${money} where userid = ${userId}";
    
    //$mysql = new mysql();//mysql数据库
    return $mysql->execute($sql);
}

?>

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1.2 问题分析

如果有两个操作人(p和m)，都用用户编号100账户,分别在pc和手机端同时登陆，100账户总余额有1000，p操作人花200，m操作人花300。并发过程如下。

p操作人：

1 取出用户的余额1000。

2 支付后剩余 800 = 1000 - 200。

3 更新后账户余额800。

m操作人：

1 取出用户余额1000。

2 支付后剩余700 = 1000 - 300。

3 支付后账户余额700。

两次支付后，账户的余额居然还有700，应该的情况是花费了500，账户余额500才对。造成这个现象的根本原因，是并发的时候，p和m同时操作取到的余额数据都是1000。

2 加锁设计

锁的操作一般只有两步，一获取锁(getLock)；二是释放锁(releaseLock)。但现实锁的方式有很多种，可以是文件方式实现；sql实现；Memcache实现；根据这种场景我们考虑使用策略模式。

2.1 类图设计如下

2.2 php源码设计如下

LockSystem.php

<?php

/** 
 * LockSystem.php 
 * 
 * php锁机制
 * 
 * Copy right (c) 2016 http://blog.csdn.net/CleverCode 
 * 
 * modification history: 
 * -------------------- 
 * 2016/9/10, by CleverCode, Create 
 * 
 */ 

class LockSystem
{
    const LOCK_TYPE_DB = &#39;SQLLock&#39;;
    const LOCK_TYPE_FILE = &#39;FileLock&#39;;
    const LOCK_TYPE_MEMCACHE = &#39;MemcacheLock&#39;;
    
    private $_lock = null;
    private static $_supportLocks = array(&#39;FileLock&#39;, &#39;SQLLock&#39;, &#39;MemcacheLock&#39;);  
    
    public function construct($type, $options = array()) 
    {
        if(false == empty($type))
        {
            $this->createLock($type, $options);
        }
    }   

    public function createLock($type, $options=array())
    {
        if (false == in_array($type, self::$_supportLocks))
        {
            throw new Exception("not support lock of ${type}");
        }
        $this->_lock = new $type($options);
    }
    
    public function getLock($key, $timeout = ILock::EXPIRE)
    {
        if (false == $this->_lock instanceof ILock)  
        {
            throw new Exception(&#39;false == $this->_lock instanceof ILock&#39;);          
        }  
        $this->_lock->getLock($key, $timeout);   
    }
    
    public function releaseLock($key)
    {
        if (false == $this->_lock instanceof ILock)  
        {
            throw new Exception(&#39;false == $this->_lock instanceof ILock&#39;);          
        }  
        $this->_lock->releaseLock($key);         
    }   
}

interface ILock
{
    const EXPIRE = 5;
    public function getLock($key, $timeout=self::EXPIRE);
    public function releaseLock($key);
}

class FileLock implements ILock
{
    private $_fp;
    private $_single;

    public function construct($options)
    {
        if (isset($options[&#39;path&#39;]) && is_dir($options[&#39;path&#39;]))
        {
            $this->_lockPath = $options[&#39;path&#39;].&#39;/&#39;;
        }
        else
        {
            $this->_lockPath = &#39;/tmp/&#39;;
        }
       
        $this->_single = isset($options[&#39;single&#39;])?$options[&#39;single&#39;]:false;
    }

    public function getLock($key, $timeout=self::EXPIRE)
    {
        $startTime = Timer::getTimeStamp();

        $file = md5(FILE.$key);
        $this->fp = fopen($this->_lockPath.$file.&#39;.lock&#39;, "w+");
        if (true || $this->_single)
        {
            $op = LOCK_EX + LOCK_NB;
        }
        else
        {
            $op = LOCK_EX;
        }
        if (false == flock($this->fp, $op, $a))
        {
            throw new Exception(&#39;failed&#39;);
        }
       
	    return true;
    }

    public function releaseLock($key)
    {
        flock($this->fp, LOCK_UN);
        fclose($this->fp);
    }
}

class SQLLock implements ILock
{
    public function construct($options)
    {
        $this->_db = new mysql(); 
    }

    public function getLock($key, $timeout=self::EXPIRE)
    {       
        $sql = "SELECT GET_LOCK(&#39;".$key."&#39;, &#39;".$timeout."&#39;)";
        $res =  $this->_db->query($sql);
        return $res;
    }

    public function releaseLock($key)
    {
        $sql = "SELECT RELEASE_LOCK(&#39;".$key."&#39;)";
        return $this->_db->query($sql);
    }
}

class MemcacheLock implements ILock
{
    public function construct($options)
    {
        
        $this->memcache = new Memcache();
    }

    public function getLock($key, $timeout=self::EXPIRE)
    {     
        $waitime = 20000;
        $totalWaitime = 0;
        $time = $timeout*1000000;
        while ($totalWaitime < $time && false == $this->memcache->add($key, 1, $timeout)) 
        {
            usleep($waitime);
            $totalWaitime += $waitime;
        }
        if ($totalWaitime >= $time)
            throw new Exception(&#39;can not get lock for waiting &#39;.$timeout.&#39;s.&#39;);

    }

    public function releaseLock($key)
    {
        $this->memcache->delete($key);
    }
}

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3 应用锁机制

3.1 支付系统应用锁

<?php

/** 
 * pay.php 
 * 
 * 支付应用锁
 * 
 * Copy right (c) 2016 http://blog.csdn.net/CleverCode 
 * 
 * modification history: 
 * -------------------- 
 * 2016/9/10, by CleverCode, Create 
 * 
 */  

//用户支付
function pay($userId,$money)
{
    
    if(false == is_int($userId) || false == is_int($money))
    {
        return false;
    }  
    
    try
    {
        //创建锁(推荐使用MemcacheLock)
        $lockSystem = new LockSystem(LockSystem::LOCK_TYPE_MEMCACHE);             
        
        //获取锁
        $lockKey = &#39;pay&#39;.$userId;
        $lockSystem->getLock($lockKey,8);
        
        //取出总额
        $total = getUserLeftMoney($userId);
        
        //花费大于剩余
        if($money > $total)
        {
            $ret = false;    
        }
        else
        { 
            //余额
            $left = $total - $money;
            
            //更新余额
            $ret = setUserLeftMoney($userId,$left);
        }
        
        //释放锁
        $lockSystem->releaseLock($lockKey); 
    }
    catch (Exception $e)
    {
        //释放锁
        $lockSystem->releaseLock($lockKey);     
    }

}

//取出用户的余额
function getUserLeftMoney($userId)
{
    if(false == is_int($userId))
    {
        return 0;
    }
    $sql = "select account form user_account where userid = ${userId}";
    
    //$mysql = new mysql();//mysql数据库
    return $mysql->query($sql);
}

//更新用户余额
function setUserLeftMoney($userId,$money)
{
    if(false == is_int($userId) || false == is_int($money))
    {
        return false;
    }        
    
    $sql = "update user_account set account = ${money} where userid = ${userId}";
    
    //$mysql = new mysql();//mysql数据库
    return $mysql->execute($sql);
}

?>

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