RFR: 8264016: [JVMCI] add some thread local fields for use by JVMCI

[Coleen Phillimore]

On Tue, 23 Mar 2021 06:11:44 GMT, Tom Rodriguez <never at openjdk.org> wrote:

> 8264016: [JVMCI] add some thread local fields for use by JVMCI

We made the _threadObj field in JavaThread an OopStorage to avoid a crash during thread deletion.  It's not recommended to add oops directly to runtime data structures.  I have to dig up the bug first.

> I haven't done a deep analysis of how much could be recovered but I could look into reducing the overall size JavaThread by > repacking if it makes adding these fields more palatable.

We have this sort of on our (internal) list with other improvements, so don't do anything here.
We also had a JVMCI bug that suggested adding these fields to a side .hpp file and referring to it in JavaThread by that container.  Like HandshakeState.  You can optimize the field layout inside this as you want.

I'm marking "Request changes" until I've had time to dig up the bug.

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Changes requested by coleenp (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/3147