@Override
 public void stop() {
   session.removeActivityProducer(this);
   session.removeActivityConsumer(consumer);
   session.removeListener(sessionListener);
   editor.removeSharedEditorListener(followModeListener);
   collector.flushFollowModes();
 }
 @Override
 public void sessionEnded(ISarosSession session, SessionEndReason reason) {
   session.removeListener(sessionListener);
   setEnabledInSWTThread(true);
 }