[crac] RFR: Selectable Global Context implementation

[Radim Vansa]

On Mon, 26 Jun 2023 16:12:24 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

> A number of problems were caused by switching to BlockingOrderedContext in the JDK code. To prevent the same in the potential users of EA builds, I temporarily switch the default implementation to the previous OrderedContext. The BlockingContext is still available via a command line option. After an EA build and transition of CRaC development to track newer version openjdk/jdk, the default implementation will be changed.
> 
> To make properties available, it was required to delay Reference resource registration. Otherwise, the GlobalContext implementation decision had to be done too early, in the Reference initialization during JDK bootstrapping, before Properties are available.

src/java.base/share/classes/jdk/crac/Core.java line 77:

> 75:     private static final Context<Resource> globalContext = GlobalContext.createGlobalContextImpl();
> 76: 
> 77:     private static class ReferenceHandlerResource implements JDKResource {

I wouldn't pollute the `Core` class with domain-specific code; if the 'reliability' of registration is of concern I think it's fine to expose the static `ensureRegistered`/`register` method.
Or, at least refactor this into its own file.

src/java.base/share/classes/jdk/crac/impl/GlobalContext.java line 8:

> 6: 
> 7: public class GlobalContext {
> 8:     private static final String GLOBAL_CONTEXT_IMPL_PROP = "jdk.crac.globalContext.impl";

As mentioned in off-GH conversation, I don't think this option would be ever used, and if you are going to change the default I'd rather drop it to keep the code simple.

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PR Review Comment: https://git.openjdk.org/crac/pull/87#discussion_r1245086510
PR Review Comment: https://git.openjdk.org/crac/pull/87#discussion_r1245089177