RFR: 8286830: ~HandshakeState should not touch oops

[Robbin Ehn]

On Mon, 30 May 2022 21:51:37 GMT, David Holmes <dholmes at openjdk.org> wrote:

> A handshake with a thread is only needed to interact with that thread in some way and we don't interact with "terminated" threads - so no handshakes needed.

We interact with all JT on a ThreadsList, that's what ThreadsList do, stop the JT from exiting so we can interact with it.

> 4. barrier_set()->on_thread_deatch() -> no more oop interaction so no need for further safepoints

Safepoints and handshakes are the same, a GC needs to beable to access the GC data in the JT until 4.
Regardless if the GC choose to access them via handshake or a safepoint.

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PR: https://git.openjdk.java.net/jdk/pull/8795