On Mon, 23 Dec 2024 17:18:15 GMT, Phil Race <p...@openjdk.org> wrote:
> The problem is that Boolean will be a value type in the future (Project
> Valhalla)
> and so it can't be the referent of a Reference.
>
> In this code, the abstract class that creates the Reference accepts a generic
> type so isn't in control of what it receives.
>
> The concrete class that extends the generic class has no idea what the super
> class implementation does,
> so has no way to know that it might do something that is invalid for a value
> type.
>
> That's an interesting observation for Valhalla (that the code that does
> something inappropriate for a value type
> isn't the source of the value type) but I don't think we need to be concerned
> about that here because we can see reasons to do this anyway.
>
> The specific classes exist because a nominal singleton for the VM may need to
> be private to an AppContext.
> This is a concept from applets but also from webstart where we have a single
> JVM that may be running code
> from different origins that needs to be partitioned and sand boxed.
>
> This concept is obsolete now as applets and webstart are no longer supported,
> and the Security Manager
> is disabled, further undermining any way to support partitioning.
>
> This specific case of a Boolean created from the value of a Java System
> Property looks like it never needed
> this partitioning, so the minimal fix is to stop using RecyclableSingleton
> for it, and just cache the value of that.
>
> The next level of fix is to note that since AppContext is obsolete, there is
> no need for RecyclableSingleton
> to use AppContext specific values, making RecyclableSingleton just a lazy
> initialization mechanism for the singleton.
>
> Given that removing the obsolete AppContext is on the TBD list - and some JDK
> components have already
> removed per-AppContext code - and we'd probably come back to this in JDK 25
> anyway it seems best
> to get it over with.
>
> That does mean that one other place in sun.awt.ImageCache needed to be
> updated too.
>
> Also one test that explicitly checked that AppContexts were used for UI
> instances is obsolete and removed.
>
> Note that RecyclableSingleton also offers some lazy initialisation benefit,
> and is widely used in Aqua,
> so going further and removing that probably isn't something we want to do at
> all, and certainly not here.
src/java.desktop/macosx/classes/com/apple/laf/AquaUtils.java line 155:
> 153: T instance;
> 154:
> 155: final T get() {
It is used in a few places to cache the fonts/images/etc, so to be a
"Recyclable" + "Singleton" it should store/return soft reference, and somehow
handle the value types properly.
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PR Review Comment: https://git.openjdk.org/jdk/pull/22868#discussion_r1899868384
