自旋锁的简单实现

public class AtomicStringBuilder {
    private AtomicReference<Thread> sign =new AtomicReference<Thread>();
    StringBuilder sb = new StringBuilder();
    public void lock(){
        Thread current = Thread.currentThread();
        while(!sign .compareAndSet(null, current)){

        }
    }

    public void unlock (){
        Thread current = Thread.currentThread();
        sign.compareAndSet(current, null);

    }
    public void append(String str){
        lock();
        sb.append(str);
        unlock();
    }
    public  void setLength(int i){
        lock();
        sb.setLength(i);
        unlock();
    }
    public String toString(){
        String str = null;
        lock();
        str=  sb.toString();
        unlock();
        return str;
    }
}

 引用：http://ifeve.com/java_lock_see1/