For some scenarios where concurrent access by the same user needs to be restricted, if the user has many concurrent requests times, and there is no lock limit for server processing, and users 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(可以换领)
B(执行换领)
C(更新为已换领)D(结束)If users submit redemption codes concurrently, they can pass the judgment that they can redeem (A), because there must be one to perform the redemption (B) will be updated to redeemed (C). Therefore, if the user makes multiple requests before there is an update as redeemed, these requests can be executed successfully.
Using file locks can achieve concurrent access restrictions, but for a distributed architecture environment, using file locks cannot guarantee the security of multiple servers. Concurrent access limits.
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. setnxieSet it Not eXists.
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['host'],
$this->_config['port'],$this->_config['timeout'],
$this->_config['reserved'],$this->_config['retry_interval']);
if(empty($this->_config['auth'])){
$redis->auth($this->_config['auth']);
}
$redis->select($this->_config['index']);
}catch(RedisException $e){
throw new Exception($e->getMessage());
return false;
}
return $redis;
}
} // class end?>demo.php
<?php
require 'RedisLock.class.php';
$config = array( 'host' => 'localhost', 'port' => 6379, 'index' => 0, 'auth' => '', 'timeout' => 1,
'reserved' => NULL, 'retry_interval' => 100,
);
// 创建redislock对象$oRedisLock = new RedisLock($config);
// 定义锁标识$key = 'mylock';
// 获取锁$is_lock = $oRedisLock->lock($key, 10);
if($is_lock){
echo 'get lock success<br>';
echo 'do sth..<br>';
sleep(5);
echo 'success<br>';
$oRedisLock->unlock($key);
// 获取锁失败
}
else{
echo 'request too frequently<br>';
}?>
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 acquire the lock, it will output request too frequently
to 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 deadlock. The problem.
Source code download address: click to view
For some users who need to limit concurrency In the access scenario, if the user makes multiple concurrent requests and the server process has no locking restrictions, the user can make multiple successful requests.
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(可以换领)
B(执行换领)
C(更新为已换领)D(结束)If users submit redemption codes concurrently, they can pass the judgment that they can redeem (A), because there must be one to perform the redemption (B) will be updated to redeemed (C). Therefore, if the user makes multiple requests before there is an update as redeemed, these requests can be executed successfully.
Using file locks can achieve concurrent access restrictions, but for a distributed architecture environment, using file locks cannot guarantee the security of multiple servers. Concurrent access limits.
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. setnxieSet it Not eXists.
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['host'],
$this->_config['port'],
$this->_config['timeout'],
$this->_config['reserved'],
$this->_config['retry_interval']);
if(empty($this->_config['auth'])){
$redis->auth($this->_config['auth']);
}
$redis->select($this->_config['index']);
}catch(RedisException $e){ throw new Exception($e->getMessage());
return false;
} return $redis;
}
} // class end?>demo.php
<?phprequire 'RedisLock.class.php';
$config = array( 'host' => 'localhost', 'port' => 6379, 'index' => 0, 'auth' => '', 'timeout' => 1,
'reserved' => NULL, 'retry_interval' => 100,
);
// 创建redislock对象$oRedisLock = new RedisLock($config);
// 定义锁标识$key = 'mylock';
// 获取锁$is_lock = $oRedisLock->lock($key, 10);
if($is_lock){
echo 'get lock success<br>';
echo 'do sth..<br>';
sleep(5);
echo 'success<br>';
$oRedisLock->unlock($key);
// 获取锁失败
}
else{
echo 'request too frequently<br>';
}?>
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 acquire the lock, it will output request too frequently
to 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 deadlock. The problem.
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