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
protected void rulerContextMenuAboutToShow(IMenuManager menu) {
		super.rulerContextMenuAboutToShow(menu);
		IMenuManager foldingMenu= new MenuManager(JavaEditorMessages.getString("Editor.FoldingMenu.name"), "projection"); 
		menu.appendToGroup(ITextEditorActionConstants.GROUP_RULERS, foldingMenu);
		
		IAction action= getAction("FoldingToggle"); 
		foldingMenu.add(action);
		action= getAction("FoldingExpandAll"); 
		foldingMenu.add(action);
	}
	
	
	/*
	 * @see org.eclipse.ui.texteditor.AbstractDecoratedTextEditor#collectContextMenuPreferencePages()
	 * @since 3.1
	 */
	protected String[] collectContextMenuPreferencePages() {
		String[] ids= super.collectContextMenuPreferencePages();
		String[] more= new String[ids.length + 6];
		more[0]= "org.eclipse.jdt.ui.preferences.JavaEditorPreferencePage"; 
		more[1]= "org.eclipse.jdt.ui.preferences.JavaTemplatePreferencePage"; 
		more[2]= "org.eclipse.jdt.ui.preferences.CodeAssistPreferencePage"; 
		more[3]= "org.eclipse.jdt.ui.preferences.JavaEditorHoverPreferencePage"; 
		more[4]= "org.eclipse.jdt.ui.preferences.JavaEditorColoringPreferencePage"; 
		more[5]= "org.eclipse.jdt.ui.preferences.SpellingPreferencePage"; 
		System.arraycopy(ids, 0, more, 6, ids.length);
		return more;
	}
}