“Singleton”模式

下面给出三种实现方法，分别给出优缺点。

方法一：

public sealed class Singleton
{
   private static readonly Singleton instance = new Singleton();
   
   private Singleton(){}

   public static Singleton Instance
   {
      get
      {
         return instance;
      }
   }
}

优点：简单明了
缺点：耗费资源

方法二：

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)
                    {
                        //...custom code
                        instance = new ClassicSingleton();
                    }
                }
            }

            return instance;
        }
    }
}

优点：节省资源
缺点：代码冗长

方法三：

 

优点：既节省资源，又简单明了
缺点：线程不安全？？？

方法四：

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();
    }
}

优点：既节省资源，又简单明了，线程也同步了（一箭三雕）
缺点：轻微冗长

说明：前面三种方法都没有线程同步（真的需要同步吗？）

public sealed class Singleton
{
    static Singleton(){Instance = new Singleton();}

    private Singleton(){}

    public static Singleton Instance{get; private set;}
}

 

http://www.cnblogs.com/k-sharp/archive/2010/05/26/1744121.html