线程安全的单例（双if）

直接上代码

namespace Test
{    
    public class SingletonTest
    {
        object Lock = new object();
        public static SingletonTest _singletonTest = null;

        public SingletonTest CreateInstace()
        {
            if (_singletonTest == null)
            {
                lock (Lock)
                {
                    if (_singletonTest == null)
                    {
                        _singletonTest = new SingletonTest();
                    }
                }
            }
            return _singletonTest;
        }
    }
}