docs: private synchronized void rootWindowClosing(WindowEvent evt) {
          // Notify to all the debuggers to stop debugging
          for (EnhancedDebugger debugger : debuggers) {
              debugger.cancel();
          }
          // Release any reference to the debuggers
          debuggers.clear();
          // Release the default instance
          instance = null;
          frame = null;
          notifyAll();
      }