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
public void gotoMatchingBracket() {
		
		ISourceViewer sourceViewer= getSourceViewer();
		IDocument document= sourceViewer.getDocument();
		if (document == null)
			return;
		
		IRegion selection= getSignedSelection(sourceViewer);
		int selectionLength= Math.abs(selection.getLength());
		if (selectionLength > 1) {
			setStatusLineErrorMessage(JavaEditorMessages.getString("GotoMatchingBracket.error.invalidSelection"));			
			sourceViewer.getTextWidget().getDisplay().beep();
			return;
		}
		
		int sourceCaretOffset= selection.getOffset() + selection.getLength();
		if (isSurroundedByBrackets(document, sourceCaretOffset))
			sourceCaretOffset -= selection.getLength();
		IRegion region= fBracketMatcher.match(document, sourceCaretOffset);
		if (region == null) {
			setStatusLineErrorMessage(JavaEditorMessages.getString("GotoMatchingBracket.error.noMatchingBracket"));			
			sourceViewer.getTextWidget().getDisplay().beep();
			return;		
		}
		
		int offset= region.getOffset();
		int length= region.getLength();
		
		if (length < 1)
			return;