Bug 81983 [preferences] Disabling and enabling folding on small file takes forever
3.1 M4 Using enable/disable folding on a small CU takes forever. This is caused by the recent change to apply the preference to all Java editors. In another (hidden) window (Debug) I had StyledText open which (understandably) took long to react on the preference change. Non-visible editor's should not react to this change until they become visible.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/JavaEditor.java
if (textWidget == null)
				return;
				
			try {
				ISourceRange range= null;
				if (reference instanceof ILocalVariable) {
					IJavaElement je= ((ILocalVariable)reference).getParent();
					if (je instanceof ISourceReference)
						range= ((ISourceReference)je).getSourceRange();
				} else
					range= reference.getSourceRange();
				
				if (range == null)
					return;
				
				int offset= range.getOffset();
				int length= range.getLength();
				
				if (offset < 0 || length < 0)
					return;
				
				setHighlightRange(offset, length, moveCursor);
				if (!moveCursor)
					return;
											
				offset= -1;
				length= -1;
				
				if (reference instanceof IMember) {
					range= ((IMember) reference).getNameRange();