RFR: 8287812: Cleanup JDWP agent GetEnv initialization [v2]

[Chris Plummer]

On Mon, 12 Dec 2022 16:28:27 GMT, Alan Bateman <alanb at openjdk.org> wrote:

> I don't mind. For now (JDK 19 and 20), the case where it will only likely arise is -agentlib:jdwp --enable-preview on ports that don't have VM continuations. In that case, GetEnv will fail. If virtual threads become permanent in JDK 21 and JVMTI is not updated to work with the alternative implementation of virtual threads then we might have to expand the error message a bit.

Seems like that is going to be an issue for any JVMTI agent, and I'm not too sure how we would determine the issue is a lack of JVMTI support on the platform. Is seems JVMTI is currently returning EVERSION when it is not supported, which isn't all the useful in determining the underlying reason.

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PR: https://git.openjdk.org/jdk/pull/11602