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 (range != null) {
						offset= range.getOffset();
						length= range.getLength();
					}
				} else if (reference instanceof ILocalVariable) {
					range= ((ILocalVariable)reference).getNameRange();
					if (range != null) {
						offset= range.getOffset();
						length= range.getLength();
					}
				} else if (reference instanceof IImportDeclaration) {
					String name= ((IImportDeclaration) reference).getElementName();
					if (name != null && name.length() > 0) {
						String content= reference.getSource();
						if (content != null) {
							offset= range.getOffset() + content.indexOf(name);
							length= name.length();
						}
					}
				} else if (reference instanceof IPackageDeclaration) {
					String name= ((IPackageDeclaration) reference).getElementName();
					if (name != null && name.length() > 0) {
						String content= reference.getSource();
						if (content != null) {
							offset= range.getOffset() + content.indexOf(name);
							length= name.length();
						}
					}
				}