public boolean isEmpty() {
        return peek() == null;
    }
This is an O(n) operation as we run through all the nodes and count them.<br>
The accuracy of the value returned by this method is subject to races with producer/consumer threads. In
particular when racing with the consumer thread this method may under estimate the size.<br>
Note that passing nodes between queues, or concurrent requeuing of nodes can cause this method to return strange
values.
jctools-experimental/src/main/java/org/jctools/queues/intrusive/MpscIntrusiveLinkedQueue.java