java 非阻塞的栈

本例中的非阻塞算法中能确保线程的安全性。
本例是摘自《JAVA并发编程实战》这本书的高级题部分

 
import java.util.concurrent.atomic.AtomicReference;

/**
 * Created by nspace on 15-4-18.
 */
//@ThreadSafe
public class CocurrentStack<E> {
    AtomicReference<Node<E>> top = new AtomicReference<Node<E>>();

    public void push(E item) {
        Node<E> newHead = new Node<E>(item);
        Node<E> oldHead;
        do {
            oldHead = top.get();
            newHead.next = oldHead;
        } while (!top.compareAndSet(oldHead, newHead));
    }

    public E pop() {
        Node<E> oldHead;
        Node<E> newHead;
        do {
            oldHead = top.get();
            if(oldHead == null) {
                return null;
            }
            newHead = oldHead.next;

        } while (!top.compareAndSet(oldHead, newHead));
        return oldHead.item;
    }

    private static class Node<E> {
        public final E item;
        public Node<E> next;

        private Node(E item) {
            this.item = item;
        }
    }
}