PHPRedis and Locking

I got the following two functions that I use to lock a Redis key. I am trying to prevent concurrency execution of a block of code using Redis. So what I do is use the following functions in such a way that they prevent the execution of the same code by different threads.

lockRedisKey("ABC");
CODE THAT I DON'T WANT TO RUN CONCURRENTLY!
unlockRedisKey("ABC");

Unfortunately, it doesn’t seem to work and causes an infinitely loop at lockRedisKey() until exit_time is reached. What could be wrong?

  static public function lockRedisKey($key, $value = "true") {

        $redis = RedisClient::getInstance();

        $time = microtime(true);
        $exit_time = $time + 10;
        $sleep = 10000;

        do {

            // Lock Redis with PX and NX

            $lock = $redis->setnx("lock:" . $key, $value);

            if ($lock == 1) {
                $redis->expire("lock:" . $key, "10");
                return true;
            }

            usleep($sleep);

        } while (microtime(true) < $exit_time);

        return false;

    }

    static public function unlockRedisKey($key) {

        $redis = RedisClient::getInstance();

        $redis->del("lock:" . $key);

    }

I’m aware that I might be facing deadlocks, so I decided to use transactions, but I continue to face the issue.

    static public function lockRedisKey($key, $value = "true") {

        $redis = RedisClient::getInstance();

        $time = microtime(true);
        $exit_time = $time + 10;
        $sleep = 10000;

        do {

            // Lock Redis with PX and NX

            $redis->multi();
            $redis->set('lock:' . $key, $value, array('nx', 'ex' => 10));
            $ret = $redis->exec();

            if ($ret[0] == true) {
                return true;
            }

            usleep($sleep);

        } while (microtime(true) < $exit_time);

        return false;

    }

    static public function unlockRedisKey($key) {

        $redis = RedisClient::getInstance();

        $redis->multi();
        $redis->del("lock:" . $key);
        $redis->exec();

    }