基于AtomicReference的单例模式写法

AtomicReference类主要属性(来源于jdk1.7中的源码)

public class AtomicReference<V> implements java.io.Serializable {
    private static final long serialVersionUID = -1848883965231344442L;

    private static final Unsafe unsafe = Unsafe.getUnsafe();
    private static final long valueOffset;

    static {
        try {
            valueOffset = unsafe.objectFieldOffset
                (AtomicReference.class.getDeclaredField("value"));
        } catch (Exception ex) { throw new Error(ex); }
    }

    private volatile V value;
    .......

}

采用AtomicRerence编写的单例模式

 public class Singleton {

     private static AtomicReference<Singleton> singleton = new AtomicReference<Singleton>();

     private Singleton(){}

     public static Singleton getInstance() {

         for(;;) {
             Singleton instance = singleton.get();
             if(instance != null ) {
                 return instance;
             }
             instance = new Singleton();
             if(singleton.compareAndSet(null, instance)) {
                 return instance;
             }
         }
     }

 }