assertEquals(4, (int) mmHeap.pollLast());
    assertEquals(3, (int) mmHeap.peekLast());
    assertEquals(3, (int) mmHeap.pollLast());
    assertEquals(1, (int) mmHeap.peek());
    assertEquals(2, (int) mmHeap.peekLast());
    assertEquals(2, (int) mmHeap.pollLast());
    assertEquals(1, (int) mmHeap.peek());
    assertEquals(1, (int) mmHeap.peekLast());
    assertEquals(1, (int) mmHeap.pollLast());
    assertNull(mmHeap.peek());

    public @Nullable E peekFirst() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peekFirst();
    }

    @Override
    public @Nullable E peekLast() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peekLast();
    }

    @Override
    public boolean removeFirstOccurrence(Object o) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.removeFirstOccurrence(o);

    public @Nullable E peekFirst() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peekFirst();
    }

    @Override
    public @Nullable E peekLast() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peekLast();
    }

    @Override
    public boolean removeFirstOccurrence(Object o) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.removeFirstOccurrence(o);

        if (tagQueue.isEmpty() && !"eef".equalsIgnoreCase(qName)) {
            throw new GsaConfigException("Invalid format.");
        }
        if (COLLECTION.equalsIgnoreCase(qName) && COLLECTIONS.equalsIgnoreCase(tagQueue.peekLast())) {
            final long now = ComponentUtil.getSystemHelper().getCurrentTimeAsLong();
            final String name = attributes.getValue("Name");
            labelType = new LabelType();

    while (!stack.isEmpty()) {
      // To peek at the top two items, we need to temporarily remove one.
      NodeAndRemainingSuccessors<N> top = stack.removeLast();
      NodeAndRemainingSuccessors<N> prev = stack.peekLast();
      stack.addLast(top);

      N node = top.node;
      N previousNode = prev == null ? null : prev.node;
      if (top.remainingSuccessors == null) {
        NodeVisitState state = visitedNodes.get(node);

    while (!stack.isEmpty()) {
      // To peek at the top two items, we need to temporarily remove one.
      NodeAndRemainingSuccessors<N> top = stack.removeLast();
      NodeAndRemainingSuccessors<N> prev = stack.peekLast();
      stack.addLast(top);

      N node = top.node;
      N previousNode = prev == null ? null : prev.node;
      if (top.remainingSuccessors == null) {
        NodeVisitState state = visitedNodes.get(node);