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;
            }
        }
    }
    
}