driver-core/src/main/com/mongodb/internal/connection/ConcurrentLinkedDeque.java
Node<E> append(E element) {
            for (;;) {
                Node<E> f = getNext();
                if (f == null || f.isMarker())
                    return null;
                Node<E> x = new Node<E>(element, f, this);
                if (casNext(f, x)) {
                    f.setPrev(x); // optimistically link
                    return x;
                }
            }
        }
Node<E> append(E element) {
            for (;;) {
                Node<E> f = getNext();
                if (f == null || f.isMarker())
                    return null;
                Node<E> x = new Node<E>(element, f, this);
                if (casNext(f, x)) {
                    f.setPrev(x); // optimistically link
                    return x;
                }
            }
        }
Tries to insert a node holding element as successor, failing
if this node is deleted.

@param element the element
@return the new node, or null on failure