RFR: 8373945: vmTestbase eatMemory/ClassUnloader provoke OOME to force GC and might cause GC in other threads [v2]

[Leonid Mesnik]

On Fri, 19 Dec 2025 03:25:34 GMT, SendaoYan <syan at openjdk.org> wrote:

>> Hi all,
>> 
>> This PR use `WhiteBox.getWhiteBox().fullGC()` instead of `eatMemory` to grigger full GC. The OOME trigger by `eatMemory` may cause vmTestbase/nsk/monitoring/stress/classload tests intermittent fails when run those tests simultancely on some machines. The WB.fullGC() might be use for same purpose. It also reduce test execution time.
>> 
>> Change has been verified locally by running tests vmTestbase/nsk/monitoring/stress/classload on linux-x64.
>> 
>> Additional testing:
>> 
>> - [ ] All jtreg tests by fastdebug build
>
> SendaoYan has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Merge branch 'openjdk:master' into jbs8373945
>  - Remove unnecessary unloadClass
>  - 8373945: vmTestbase eatMemory/ClassUnloader provoke OOME to force GC and might cause GC in other threads

Thank you for fixing this. It improves reliability of testing significantly. However more changes and testing is needed.
I started discussion inline to have it in thread.

test/hotspot/jtreg/vmTestbase/nsk/share/ClassUnloader.java line 36:

> 34: import nsk.share.test.ExecutionController;
> 35: import nsk.share.test.Stresser;
> 36: import jdk.test.whitebox.WhiteBox;

This change impacts a lot of tests in vmTestbase. They are going to be broken if are using classunloading.
Si it requires testing of ALL vmTestbase tests to ensure that all test are fixed, not only monitoring.

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Changes requested by lmesnik (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/28891#pullrequestreview-3596794660
PR Review Comment: https://git.openjdk.org/jdk/pull/28891#discussion_r2633597452