Notify when controller is closed

I have a plugin that draws a spectrum analyzer by calling the processor every 30 ms (with CVSTGUITimer). Now when i close the plugin GUI in the host (processor remains alive) i want it to stop calling the processor since the user won’t be seeing anything anyway.

I have not found any function that is called whenever the controller part of the plugin is closed in the host. Is there a function for this or what is the way to go for this? I assume most plugins need to get notified when their controller part is not visible anymore to avoid unnecessary computing.

The controller is not closed, only the plugin view is closed in this case.
If you use the Vst::EditController class, the editorDestroyed method is called whenever the plugin view is closed.