[jdk20u] RFR: 8300575: JVMTI support when using alternative virtual thread implementation

[Tyler Steele]

On Mon, 24 Apr 2023 17:02:42 GMT, Tyler Steele <tsteele at openjdk.org> wrote:

> This PR backports modifications to the jvmti code to add support for vthreads. Without this change, we see many failures in our internal testing.
> 
> These changes did not apply cleanly in several places because of changes related to JDK-8299837 (Replace NULL with nullptr in hotspot code and tests). In these places, the changes expected code containing nullptr, but found NULL. In these spots, kept the code from the backported change, but changed nullptr back to NULL for consistency with the rest of the code base.
> 
> Testing is underway.

Things get a bit cryptic when discussing the conformance tests, so feel free to reach out via email if you find my response is not providing the detail you're looking for.

> Are you sure this is needed[?] JVMTI is optional...

Basically, yes I'm sure. And, we've received guidance on one of the mailing lists that backporting this change is a possible solution to the difficulty we are facing.

> ... and a build with the alt implementation doesn't support JVMTI with --enable-preview.

Unless I've misunderstood your comment. Yes, but the changes I'm backporting are meant to enable it.

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PR Comment: https://git.openjdk.org/jdk20u/pull/60#issuecomment-1520618448