nonblocking stack in java [closed]

Question

Can somebody help me in writing a non-blocking, lock free stack implementation. Is it there in the Sun java implementation?

I was trying to write a thread safe Stack by putting a global lock on the whole stack data structure (it is costly) but it seems that it is possible to write a non-blocking, lock free stack.

An algorithm is called nonblocking if it is lock free and immune of deadlock.

Answer 1

public class MyConcurrentStack<T> {

    private AtomicReference<Node> head = new AtomicReference<Node>();

    public MyConcurrentStack() {
    }

    public void push(T t) {
        if (t == null) {
            return;
        }
        Node<T> n = new Node<T>(t);
        Node<T> current;

        do {
            current = head.get();
            n.setNext(current);
        } while (!head.compareAndSet(current, n));
    }

    public T pop() {
        Node<T> currentHead = null;
        Node<T> futureHead = null;
        do {
            currentHead = head.get();
            if (currentHead == null) {
                return null;
            }
            futureHead = currentHead.next;
        } while (!head.compareAndSet(currentHead, futureHead));

        return currentHead.data;
    }

    /**
     *
     * @return null if no element present else return a element. it does not
     * remove the element from the stack.
     */
    public T peek() {
        Node<T> n = head.get();
        if (n == null) {
            return null;
        } else {
            return n.data;
        }
    }

    public boolean isEmpty() {
        if (head.get() == null) {
            return true;
        }
        return false;
    }

    private static class Node<T> {

        private final T data;
        private Node<T> next;

        private Node(T data) {
            this.data = data;
        }

        private void setNext(Node next) {
            this.next = next;
        }
    }
}

Answer 2

concurrent stack java first google result

Queues

The java.util.concurrent ConcurrentLinkedQueue class supplies an efficient scalable thread-safe non-blocking FIFO queue. Five implementations in java.util.concurrent support the extended BlockingQueue interface, that defines blocking versions of put and take: LinkedBlockingQueue, ArrayBlockingQueue, SynchronousQueue, PriorityBlockingQueue, and DelayQueue. The different classes cover the most common usage contexts for producer-consumer, messaging, parallel tasking, and related concurrent designs. The BlockingDeque interface extends BlockingQueue to support both FIFO and LIFO (stack-based) operations. Class LinkedBlockingDeque provides an implementation.