safe way to get a singleton instance from multithreads

Method 1

DataCenter* DataCenter::getInstance()
{
    static DataCenter instance;
    return &instance;    
}

Method 2

DataCenter* DataCenter::getInstance()
{
    if (!m_instanceFlag)
    {
        m_instance = new DataCenter();
        m_instanceFlag = true;
    }    
    return m_instance;      
}

I am working on a multi threaded programming and DataCenter will be accessed by more than one thread. I used to have method 2 to get the instance of DataCenter and it worked fine. But I noted that I need to guard the singleton instance from being called by multi threads.

My question is first do I really need to guard the singleton instance? or does OS do this for me? Second questions is that, is the first method a right way to get the singleton instance?

Thanks in advance...