Bug 52474 UI Blocked when opening Java Perspective during CVS check out
build I20040218 - start eclipse with a new workspace - switch to CVS Repository Exploring perspective - check out a number of projects ( i checkout Platform UI module) - now attempt to switch to the Java Perspective NOTE that at this point the "UI is blocked" dialog is opened. Probably due to the fact that starting the Java Perspective requires the workbench lock? The point here is that this will be a common pattern and it would be nice if we could investigate makeing this scenario work more smoothly.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerPart.java
fillActionBars();
		updateTitle();
		
		fFilterUpdater= new FilterUpdater(fViewer);
		ResourcesPlugin.getWorkspace().addResourceChangeListener(fFilterUpdater);
	}
	private void initFrameActions() {
		fActionSet.getUpAction().update();
		fActionSet.getBackAction().update();
		fActionSet.getForwardAction().update();
	}
	/**
	 * This viewer ensures that non-leaves in the hierarchical
	 * layout are not removed by any filters.
	 * 
	 * @since 2.1
	 */
	private ProblemTreeViewer createViewer(Composite composite) {
		return  new ProblemTreeViewer(composite, SWT.MULTI | SWT.H_SCROLL | SWT.V_SCROLL) {
			/*
			 * @see org.eclipse.jface.viewers.StructuredViewer#filter(java.lang.Object)
			 */
			protected Object[] getFilteredChildren(Object parent) {
				List list = new ArrayList();
				ViewerFilter[] filters = fViewer.getFilters();
				Object[] children = ((ITreeContentProvider) fViewer.getContentProvider()).getChildren(parent);
				for (int i = 0; i < children.length; i++) {
					Object object = children[i];
					if (!isEssential(object)) {