Redis 实现分布式锁

require_once("../RedisClient.php");
$client = RedisClient::getInstance();
/**
 * 基础版,完成锁的请求与释放,但是有严重的问题.
 * 如果请求锁完成后,宕机了,就成死锁了.再也不能请求到锁了
 * @return null
 */
function base () {
    global $client;
    //请求锁
    $lock = $client->set('lock','true');
    if(!$lock){
        return null;
    }

    // do something critical ...

    //释放锁
    $client->del('lock');
}

require_once("../RedisClient.php");
$client = RedisClient::getInstance();
/**
 * 设置锁和添加过期时间放在一个命令中,要成功一起成功
 * 添加随机数，防止过期时间后，删除了其他进程的锁
 * @return null
 */
function perfect () {
    global $client;
    $unique = uniqid();
    //请求锁并添加过期时间
    $lock = $client->set('lock',$unique,'ex',60,'nx');
    if(!$lock){
        return null;
    }

    // do something critical ...

    //释放锁
    if ($client->get('lock')==$unique){
        $client->del('lock');
    };
}

use Predis\Command\ScriptCommand;
require_once("../RedisClient.php");
$client = RedisClient::getInstance();

class releaseLockScript extends ScriptCommand {

    public function getScript()
    {
        return <<<LUA
if redis.call("get",ARGV[1]) == ARGV[2] then
    return redis.call("del",ARGV[1])
else
    return 0
end
LUA;
    }
}
// 定义锁命令
$client->getProfile()->defineCommand('releaseLock','releaseLockScript');
function lua () {
    global $client;
    $unique = uniqid();
    //请求锁并添加过期时间
    $lock = $client->set('lock',$unique,'ex',60,'nx');
    if(!$lock){
        return null;
    }

    // do something critical ...

    //释放锁
    $client->releaseLock('lock',$unique)
}