private void enqueue(E x) {
    // assert putLock.isHeldByCurrentThread();
    // assert last.next == null;
    last = last.next = new Node<>(x);
  }
Creates a node and links it at end of queue.

@param x the item
geode-core/src/main/java/org/apache/geode/internal/cache/ForceableLinkedBlockingQueue.java