C#标准单例模式实现

singleton.cs

public class ClassA
{
    private static ClassA _instance = null;
    private static readonly object Padlock = new object();

    ClassA() { }

    public static ClassA Instance
    {
        get
        {
            if (_instance == null)
            {
                lock (Padlock)
                {
                    if (_instance == null)
                    {
                        _instance = new ClassA();
                    }
                }
            }
            return _instance;
        }
    }
}