package net.jcip.examples;

import java.util.concurrent.atomic.*;

import net.jcip.annotations.*;

/**

* ConcurrentStack

* <p/>

* Nonblocking stack using Treiber's algorithm

*

* @author Brian Goetz and Tim Peierls

*/

@ThreadSafe

public class ConcurrentStack <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;

public Node(E item) {

this.item = item;

}

}

}