在工作項目中，會遇到一些php並發訪問去修改一個數據問題，如果這個數據不加鎖，就會造成數據的錯誤。下面我將分析一個財務支付鎖的問題。希望對大家有所幫助。
1 沒有應用鎖機制
1.1 財務支付簡化版本代碼
<!--?php
/**
* pay.php
*
* 支付沒有應用鎖
*
* Copy right (c) 2016
*
* modification history:
* --------------------
* 2016/9/10, by CleverCode, Create
*
*/
//用戶支付
function pay($userId,$money)
{
if(false == is_int($userId) || false == is_int($money))
{
return false;
}
//取出總額
$total = getUserLeftMoney($userId);
//花費大於剩余
if($money --> $total)
{
return false;
}
//余額
$left = $total - $money;
//更新余額
return setUserLeftMoney($userId,$left);
}
//取出用戶的余額
function getUserLeftMoney($userId)
{
if(false == is_int($userId))
{
return 0;
}
$sql = "select account form user_account where userid = ${userId}";
//$mysql = new mysql();//mysql數據庫
return $mysql->query($sql);
}
//更新用戶余額
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數據庫
return $mysql->execute($sql);
}
?>
1.2 問題分析
如果有兩個操作人(p和m)，都用用戶編號100賬戶,分別在pc和手機端同時登陸，100賬戶總余額有1000，p操作人花200，m操作人花300。並發過程如下。
p操作人：
m操作人：
兩次支付後，賬戶的余額居然還有700，應該的情況是花費了500，賬戶余額500才對。造成這個現象的根本原因，是並發的時候，p和m同時操作取到的余額數據都是1000。
2 加鎖設計
鎖的操作一般只有兩步，一 獲取鎖(getLock)；二是釋放鎖(releaseLock)。但現實鎖的方式有很多種，可以是文件方式實現；sql實現；Memcache實現；根據這種場景我們考慮使用策略模式。
2.1 類圖設計如下
2.2 php源碼設計如下
LockSystem.php
<!--?php
/**
* LockSystem.php
*
* php鎖機制
*
* Copy right (c) 2016
*
* modification history:
* --------------------
* 2016/9/10, by CleverCode, Create
*
*/
class LockSystem
{
const LOCK_TYPE_DB = 'SQLLock';
const LOCK_TYPE_FILE = 'FileLock';
const LOCK_TYPE_MEMCACHE = 'MemcacheLock';
private $_lock = null;
private static $_supportLocks = array('FileLock', 'SQLLock', 'MemcacheLock');
public function __construct($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('false == $this->_lock instanceof ILock');
}
$this->_lock->getLock($key, $timeout);
}
public function releaseLock($key)
{
if (false == $this->_lock instanceof ILock)
{
throw new Exception('false == $this->_lock instanceof ILock');
}
$this->_lock->releaseLock($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($options['path']) && is_dir($options['path']))
{
$this->_lockPath = $options['path'].'/';
}
else
{
$this->_lockPath = '/tmp/';
}
$this->_single = isset($options['single'])?$options['single']:false;
}
public function getLock($key, $timeout=self::EXPIRE)
{
$startTime = Timer::getTimeStamp();
$file = md5(__FILE__.$key);
$this->fp = fopen($this->_lockPath.$file.'.lock', "w+");
if (true || $this->_single)
{
$op = LOCK_EX + LOCK_NB;
}
else
{
$op = LOCK_EX;
}
if (false == flock($this->fp, $op, $a))
{
throw new Exception('failed');
}
return true;
}
public function releaseLock($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)
{
$sql = "SELECT GET_LOCK('".$key."', '".$timeout."')";
$res = $this->_db->query($sql);
return $res;
}
public function releaseLock($key)
{
$sql = "SELECT RELEASE_LOCK('".$key."')";
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 >= $time)
throw new Exception('can not get lock for waiting '.$timeout.'s.');
}
public function releaseLock($key)
{
$this->memcache->delete($key);
}
}
3 應用鎖機制
3.1 支付系統應用鎖
<!--?php
/**
* pay.php
*
* 支付應用鎖
*
* Copy right (c) 2016
*
* modification history:
* --------------------
* 2016/9/10, by CleverCode, Create
*
*/
//用戶支付
function pay($userId,$money)
{
if(false == is_int($userId) || false == is_int($money))
{
return false;
}
try
{
//創建鎖(推薦使用MemcacheLock)
$lockSystem = new LockSystem(LockSystem::LOCK_TYPE_MEMCACHE);
//獲取鎖
$lockKey = 'pay'.$userId;
$lockSystem--->getLock($lockKey,8);
//取出總額
$total = getUserLeftMoney($userId);
//花費大於剩余
if($money > $total)
{
$ret = false;
}
else
{
//余額
$left = $total - $money;
//更新余額
$ret = setUserLeftMoney($userId,$left);
}
//釋放鎖
$lockSystem->releaseLock($lockKey);
}
catch (Exception $e)
{
//釋放鎖
$lockSystem->releaseLock($lockKey);
}
}
//取出用戶的余額
function getUserLeftMoney($userId)
{
if(false == is_int($userId))
{
return 0;
}
$sql = "select account form user_account where userid = ${userId}";
//$mysql = new mysql();//mysql數據庫
return $mysql->query($sql);
}
//更新用戶余額
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數據庫
return $mysql->execute($sql);
}
?>
3.2 鎖分析
p操作人：
m操作人：
兩次支付後，余額500。非常完美了解決了並發造成的臨界區資源的訪問問題。
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