题目是实现一个无锁的Stack，并写一段测试代码（多线程访问），证明这个Stack是线程安全的。


public class TestCAS {

    static LockFreeStack<Object> stack = new LockFreeStack<>();

    static class Node<T> {
        private T v;
        private Node<T> next;

        public Node(T value, Node<T> next){
            v = value; this.next = next;
        }
        public void setNext(Node<T> next){
            this.next = next;
        }
        public Node<T> getNext(){
            return next;
        }

        public void setValue(T v){
            this.v = v;
        }

        public T getValue(){
            return v;
        }
    }

    static class LockFreeStack<T>{
        AtomicStampedReference<Node<T>> top = new AtomicStampedReference<>(null,0);
        AtomicLong count = new AtomicLong(0);
        public void push(T value){
            Node<T> newvalue = new Node(value,null);
            Node<T> oldvalue = null;
            int stamp = 0;
            do {
                stamp = top.getStamp();
                oldvalue = top.getReference();
                newvalue.setNext(oldvalue);
            } while(!top.compareAndSet(oldvalue,newvalue,stamp,stamp+1));
            count.incrementAndGet();
            System.out.println("count2:" + count.get());
        }

        public T pop(){
            Node<T> newvalue = null;
            Node<T> oldvalue = null;
            int stamp = 0;
            do {
                stamp = top.getStamp();
                oldvalue = top.getReference();
                if(null == oldvalue){
                    continue;
                }
                newvalue = oldvalue.getNext();
            } while(null == oldvalue || !top.compareAndSet(oldvalue,newvalue,stamp,stamp+1));
            count.decrementAndGet();
            System.out.println("count:"+count.get());
            return oldvalue.getValue();
        }

        public void getCount(){
            System.out.println("All:"+count.get());
        }
    }
    static class Push extends Thread {
        @Override
        public void run() {
            for(;;) {
                stack.push("Random->"+Math.random());
                Thread.yield();
            }
        }
    }

    static class Pop extends Thread {
        @Override
        public void run() {
            for(;;) {
                stack.pop();
                Thread.yield();
                //System.out.println("已出栈：" + stack.pop());
            }
        }
    }

    public static void main(String[] args) throws InterruptedException {
        Push [] pushs = new Push[10];
        Pop [] pop = new Pop[10];
        for(int i = 0; i < 10; i++) {
            pushs[i] = new Push();
            pop[i] = new Pop();
        }
        for(int i = 0; i < 10; i++) {
            pushs[i].start();
            pop[i].start();
        }

        for (;;){
            Thread.sleep(1000);
            stack.getCount();
        }

    }
}


为什么count还会打印负数  求教