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
object = filter(object, parent, filters);
						if (object != null) {
							list.add(object);
						}
					} else
						list.add(object);
				}
				return list.toArray();
			}
			
			
			private Object filter(Object object, Object parent, ViewerFilter[] filters) {
				for (int i = 0; i < filters.length; i++) {
					ViewerFilter filter = filters[i];
					if (!filter.select(fViewer, parent, object))
						return null;
				}
				return object;
			}
		
			/* Checks if a filtered object in essential (ie. is a parent that
			 * should not be removed).
			 */ 
			private boolean isEssential(Object object) {
				try {
					if (!isFlatLayout() && object instanceof IPackageFragment) {
						IPackageFragment fragment = (IPackageFragment) object;
						return !fragment.isDefaultPackage() && fragment.hasSubpackages();
					}
				} catch (JavaModelException e) {