Bug 161086 [Viewers] performance problem in AbstractTreeViewer.internalExpandToLevel
If you expand to ALL_LEVELS, internalExpandToLevel will call createChildren even if the element has no children, i.e. it does not check if the element is expandable. Found this while experimenting with the Quick Access feature (enter "con", then delete all three characters one at a time).
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
Assert.isNotNull(elementOrTreePath);
		Widget w = internalGetWidgetToSelect(elementOrTreePath);
		if (w != null) {
			internalCollapseToLevel(w, level);
		}
	}
	/**
	 * Creates all children for the given widget.
	 * <p>
	 * The default implementation of this framework method assumes that
	 * <code>widget.getData()</code> returns the element corresponding to the
	 * node. Note: the node is not visually expanded! You may have to call
	 * <code>parent.setExpanded(true)</code>.
	 * </p>
	 * 
	 * @param widget
	 *            the widget
	 */
	protected void createChildren(final Widget widget) {
		final Item[] tis = getChildren(widget);
		if (tis != null && tis.length > 0) {
			Object data = tis[0].getData();
			if (data != null) {
				return; 
			}
		}
		BusyIndicator.showWhile(widget.getDisplay(), new Runnable() {
			public void run() {