在工作項(xiàng)目中，會(huì)遇到一些php并發(fā)訪問(wèn)去修改一個(gè)數(shù)據(jù)問(wèn)題，如果這個(gè)數(shù)據(jù)不加鎖，就會(huì)造成數(shù)據(jù)的錯(cuò)誤。下面我將分析一個(gè)財(cái)務(wù)支付鎖的問(wèn)題。希望對(duì)大家有所幫助。

1 沒(méi)有應(yīng)用鎖機(jī)制

1.1 財(cái)務(wù)支付簡(jiǎn)化版本代碼

<!--?php 
/** 
 * pay.php 
 * 
 * 支付沒(méi)有應(yīng)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(fèi)大于剩余
 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(shù)據(jù)庫(kù)
 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(shù)據(jù)庫(kù)
 return $mysql->execute($sql);
}
?>

1.2 問(wèn)題分析

如果有兩個(gè)操作人(p和m)，都用用戶編號(hào)100賬戶,分別在pc和手機(jī)端同時(shí)登陸，100賬戶總余額有1000，p操作人花200，m操作人花300。并發(fā)過(guò)程如下。

p操作人：

取出用戶的余額1000。
支付后剩余 800 = 1000 - 200。
更新后賬戶余額800。

m操作人：

取出用戶余額1000。
支付后剩余700 = 1000 - 300。
支付后賬戶余額700。

兩次支付后，賬戶的余額居然還有700，應(yīng)該的情況是花費(fèi)了500，賬戶余額500才對(duì)。造成這個(gè)現(xiàn)象的根本原因，是并發(fā)的時(shí)候，p和m同時(shí)操作取到的余額數(shù)據(jù)都是1000。

2 加鎖設(shè)計(jì)

鎖的操作一般只有兩步，一獲取鎖(getLock)；二是釋放鎖(releaseLock)。但現(xiàn)實(shí)鎖的方式有很多種，可以是文件方式實(shí)現(xiàn)；sql實(shí)現(xiàn)；Memcache實(shí)現(xiàn)；根據(jù)這種場(chǎng)景我們考慮使用策略模式。

2.1 類(lèi)圖設(shè)計(jì)如下

2.2 php源碼設(shè)計(jì)如下

LockSystem.php

<!--?php 
/** 
 * LockSystem.php 
 * 
 * php鎖機(jī)制
 * 
 * Copy right (c) 2016
 * 
 * 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('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(yīng)用鎖機(jī)制

3.1 支付系統(tǒng)應(yīng)用鎖

<!--?php
 
/** 
 * pay.php 
 * 
 * 支付應(yīng)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(chuàng)建鎖(推薦使用MemcacheLock)
  $lockSystem = new LockSystem(LockSystem::LOCK_TYPE_MEMCACHE);    
   
  //獲取鎖
  $lockKey = &#39;pay&#39;.$userId;
  $lockSystem--->getLock($lockKey,8);
   
  //取出總額
  $total = getUserLeftMoney($userId);
   
  //花費(fèi)大于剩余
  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(shù)據(jù)庫(kù)
 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(shù)據(jù)庫(kù)
 return $mysql->execute($sql);
}
?>

3.2 鎖分析

p操作人：