RFR: 8319932: [JVMCI] class unloading related tests can fail on libgraal

[David Holmes]

On Thu, 29 Feb 2024 08:20:31 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> Is there a way to do something like `WhiteBox.waitForCompilationToComplete()` prior to calling `fullGC()`?
>
> All I see is `WhiteBox.enqueueMethodForCompilation` which will only wait for a compilation when `BackgroundCompilation` is `false`. Even then, which compilation(s) should be waited for?
> 
> We also have the issue that libgraal is not always as eager to clear object handles (see [JDK-8310218](https://bugs.openjdk.org/browse/JDK-8310218)), especially in `-Xcomp` mode and the retry loop helps in that situation as well.
> If this retry logic should be in `ClassUnloadCommon.triggerUnloading`, then we'd need a second version of that method that takes a set of classes that are expected to be unloaded (e.g. `ClassUnloadCommon.triggerUnloading(String... namesOfClassesToBeUnloaded)`).

I think we would only need that second version because the first/existing one is unreliable! But given all these "incidental" things that can keep classes strongly reachable reliability may be a pipe-dream here. But even if it is just a better version I would still prefer to see this in the utility code than individual tests.

BTW if this is a C1 issue any idea why we do not see it with C1 + C2 ?

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PR Review Comment: https://git.openjdk.org/jdk/pull/18044#discussion_r1507533091