<!--"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);
}
"text-align: left;">2.1 类图设计如下




2.2 php源码设计如下
LockSystem.php


<!--"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'])"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 应用锁机制
3.1 支付系统应用锁


<!--"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);
}
?>



3.2 锁分析
p操作人：
获取锁：pay100

取出用户的余额1000。

支付后剩余 800 = 1000 - 200。

更新后账户余额800。

释放锁：pay100
m操作人：
1、等待锁：pay100

2、获取锁：pay100

3、获取余额：800

3、支付后剩余500 = 800 - 300。

5、支付后账户余额500。

6、释放锁：pay100
两次支付后，余额500。非常完美了解决了并发造成的临界区资源的访问问题。