From OpenJDK discuss: > On 21 Nov 2021, at 21:55, Alan Bateman <alan.bate...@oracle.com> wrote: > > 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. >
Indeed - a synthetic module providing a holder service might do the job. Seems somewhat cumbersome though. Would it be too much to ask for accepting a patch adding a reference to ML.Controller to ModuleLayer? It wouldn’t require changes to the spec I think as the lifetime of ML.Controller is unspecified. — Michal
