FMDatabaseQueue - how to get Query Data back

[姚小新]

    // Read DB User Version
    private class func readUserVersion() -> UInt32
    {
        var retV : UInt32 = 0;
        if (m_queue == nil)
        {
            // error log
            print("readUserVersion, queue is nil");
            return retV;
        }
       
        m_queue!.inDatabase({ (db: FMDatabase?) -> Void in
            db!.open();
            retV = db!.userVersion();
            db!.close();
        })
       
        return retV;
    }


I want to get back data in inDatabase, but retV sometimes get 0 back.
I think it is that inDatabase thread not run but retV has been returned.
I donno how to solve this problem.
Can anybody help me?