php redis common application concurrent lock. (pessimistic lock)

Redis implements pessimistic locking.

The principle is to go in and grab the lock. If the grab fails, wait a second to grab it, wait another second to grab it, and so on and so forth.

To unlock is to delete the corresponding key.  

 

/**
 * Implement redis pessimistic locking
 * User: babytuo
 */
Class RedisLock {

    public $expire = 2;

    public function test(){

         $this->lock("test1");
         echo "111";
    }


    public function lock($key){

        $redis = self::createRedisObj();
        $now = time();

        /* * Understand setnx
        If the given key already exists, SETNX does nothing.
        SETNX is shorthand for "SET if Not eXists" (SET if not present).
         */ 
        // Grab the lock. 
        $isLock = $redis ->setnx( $key , time () + $this ->expire);   // Set as the expiration time.

        //不成功
        while ( ! $isLock) {
            $now++;
            $time = $now + $this->expire;

            // Recreate 
            $lock = $redis ->setnx( $key , $time );
             if ( $lock == 1 || ( $now > $redis ->get( $key ) && $now > $redis - >getset( $key , $time ))) { // After the lock contention is successful, set a new expiration time. 
                break ;
            } else {
                sleep(1);//0.5s
            }
        }
        return true;
    }

    /**
     * Unlock
     * @param type $flag
     * @return boolean
     */
    public function unlock($key) {
        $redis = self::createRedisObj();
        $redis->del($key);
        return true;
    }

    /**
     * Check if the lock exists
     * @param $key
     * @return bool
     */
    public function checklock($key){
        $redis = self::createRedisObj();
        return $redis->exists($key);
    }





    public  static  $_redis ;
    /* *
     * Create a redis object.
     * @return Redis
     */ 
    public  static  function createRedisObj(){
         if ( ! self:: $_redis ){
             $redis = new Redis();
             $info = Yii::app()->cache->servers[0];   // read config 
            $host = $info ["host" ];
             $port = $info ["port" ];
             $redis ->connect( $host , $port );
             $redis_db = Yii::app()->settings-> get('system' , 'redis_db');   // Set the default library 
            $redis->select($redis_db);
            self::$_redis = $redis;
        }
        return self::$_redis;
    }


}