C#中三种方法实现单件模式

单件模式是一种设计模式，即保持同时只能创建一个实例，下面列出了C#实现单件模式的三种方法

方法1

public sealed Class Singleton
{
   private static ReadOnly Singleton instance = new Singleton();
 
   private Singleton(){}
 
   public static Singleton Instance
   {
      get
      {
         return instance;
      }
   }
}

方法2

public sealed Class ClassicSingleton
{
    private static ClassicSingleton instance;
    private static object SyncRoot = new Object ();
 
    private ClassicSingleton(){}
 
    public static ClassicSingleton Instance
    {
        get
        {
            if(instance == null)
            {
                lock (SyncRoot)
                {
                    if(instance == null)
                    {
                        instance = new ClassicSingleton ();
                    }
                }
            }
 
            return instance;
        }
    }
}

方法3

public Class Singleton
{
    private static Singleton instance;
    // Added a static mutex for synchronising use of instance.
    private static System.Threading.Mutex mutex;
    private Singleton(){}
    static Singleton ()
    {
        instance = new Singleton();
        mutex = new System.Threading.Mutex();
    }
 
    public static Singleton Acquire()
    {
        mutex.WaitOne ();
        return instance;
    }
 
    // Each call to Acquire () requires a call to Release()
    public static void Release()
    {
        mutex.ReleaseMutex();
    }
}