ModuleLayer.Controller strongly references Module

Alan Bateman Alan.Bateman at
Sun Nov 21 20:55:27 UTC 2021

On 21/11/2021 13:27, Michał Kłeczek wrote:
> Hello All,
> I am looking for a way to associate ModuleLayer.Controller with a Module (or ModuleLayer) in such a way that it won’t disable garbage collection of Modules and ModuleLayers.
> WeakHashMap<ModuleLayer, ModuleLayer.Controller> won’t work as Controller strongly references its ModuleLayer (which in turn strongly references Modules).
> WeakHashMap<ModuleLayer, WeakReference<ModuleLayer.Controller>> won’t work either cause controller will be garbage collected.
> So far I only came up with subclassing a ModuleReference and keeping the reference to the controller there. This won’t work in case when ModuleLayer.configuration() is used a a parent configuration.
> Am I missing something obvious here?
You are correct that a module layer doesn't keep the ML.Controller 
alive. A ML.Controller is somewhat niche object to expand the 
readability graph or maybe add additional edges to open modules, and 
then be thrown away. It sounds like you want to keep it around in order 
to do further opening when additional child layers come into being. One 
way you could do this is create a module with a holder class to keep the 
reference. So rather than keeping the reference in the model world 
(ModuleReference), instead put it as a field in a reified module. With 
the right encapsulation it should give you the module layer -> 
Controller without compromising the integrity of the layers. If you want 
to discuss further then it's probably best to follow-up on jigsaw-dev 
rather here.


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