Locking and unlocking of php redis

This article mainly introduces the locking and unlocking of php redis, which has certain reference value. Now I share it with everyone. Friends in need can refer to it

php redis implements locking and unlocking operations

Business background: Locks are needed in room chess and card games to prevent dirty reading of redis data caused by concurrent operations; for example, adding the action of a user entering the room:

In the case of concurrency, get RoomUsers will have dirty reads;

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Solution idea: Lock the room to realize that only one room can be read at a time Allow one client to operate while other concurrent clients wait; that is, ----- blocking lock;

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Lock: There are several redis locking methods: incr , set, setnx, hSetnx, you can refer to this article: Several implementations of redis locking

Here I use the set method

$roomId = $_GET['roomId'];
$user = $_GET['user'];             // '张三'
$key = "LockRoom:{$roomId}";
$value = $roomId.uniqid();
$ex = 3;
// 如果 $key 不存在的话，就设置 $key 的值为 $value，且有效期为 3s; 
// return TRUE / FALSE
while(true){
    $res  = $this->redis->set($key, $value, ['nx', 'ex' => $ex]);
    if($res) { break; }
    usleep(5000);
}

// 将用户添加进房间
$roomUsers = $this->redis->get("Room:{$roomId}:Users"); // ['李四', '王五']
$roomUsers[] = $user;
$this->redis->set("Room:{$roomId}:Users", $roomUsers); // ['李四', '王五', '张三']

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Unlocking: Of course you have to unlock it after the operation. If you don’t unlock it, you have to wait at least 3 seconds;
Use delete to delete the key to unlock; but there is a pitfall here, you cannot use delete directly, because it is assumed that client01 has obtained the lock, and after adding the user to enter the room The process time exceeds 3 seconds. At this time, client02 will also obtain the lock and set 3S. Then when client01 completes the operation and delete key, the lock set by client02 will be deleted;
It is recommended to use lua code to perform deletion, because Lua execution is atomic.

// 将用户添加进房间
$roomUsers = $this->redis->get("Room:{$roomId}:Users"); // ['李四', '王五']
$roomUsers[] = $user;
$this->redis->set("Room:{$roomId}:Users", $roomUsers); // ['李四', '王五', '张三']

// lua 脚本解锁
// 先判断 key的值是否为 value, TRUE 才会删除, 所以 $value 的设计要有随机唯一性
$script = 'if redis.call("get",KEYS[1]) == ARGV[1]
then
    return redis.call("del",KEYS[1])
else
    return 0
end ';
$this->redis->eval($script, array($key , $value), 1);

For details, you can also read this article: The correct posture to unlock the Redis lock

There is also documentation on PHP operating redis: PhpRedis contains explanations of the set() and eval() functions

Note: When using lua script here, php.ini needs to open system functions such as shell_exec()
The above code is for reference only! !

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