Bug 253773 [Viewers] Collapsed expandable nodes in a TreeViewer are needlessly expensive
In the Expressions view, the debug platform TreeViewer needlessly causes the model to be queried for all children of collapsed expandable items. This can have serious performance repercussions. This can be easily seen in a CDT gdb debug session. Create a simple C project with the following main(). Launch a debug session and add 'arr1' and 'arr2' in the Expressions view. Don't expand them. Simple step through the loop. Every step takes about 3-4 seconds on a relatively fast machine. Close the Expressions view, stepping becomes instantaneous. int main() { int arr1[100]; int arr2[100]; while (1) { int i = 1; i++; } return arr1[0] + arr2[0]; }
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/TreeViewer.java
private static final String VIRTUAL_DISPOSE_KEY = Policy.JFACE
			+ ".DISPOSE_LISTENER"; 
	/**
	 * This viewer's control.
	 */
	private Tree tree;
	/**
	 * Flag for whether the tree has been disposed of.
	 */
	private boolean treeIsDisposed = false;
	private boolean contentProviderIsLazy;
	private boolean contentProviderIsTreeBased;
	/**
	 * The row object reused
	 */
	private TreeViewerRow cachedRow;
	/**
	 * true if we are inside a preservingSelection() call
	 */
	private boolean preservingSelection;
	/**
	 * Creates a tree viewer on a newly-created tree control under the given
	 * parent. The tree control is created using the SWT style bits
	 * <code>MULTI, H_SCROLL, V_SCROLL,</code> and <code>BORDER</code>. The
	 * viewer has no input, no content provider, a default label provider, no
	 * sorter, and no filters.
	 *
	 * @param parent
	 *            the parent control
	 */