RFR: 8350314: Shenandoah: Capture thread state sync times in GC timings [v2]

[Xiaolong Peng]

On Wed, 26 Feb 2025 00:02:45 GMT, Xiaolong Peng <xpeng at openjdk.org> wrote:

>> I'm also currently working on removing the `final_roots` safepoint and fixing up the phase timings for the newish concurrent init update refs phase.
>
> Sorry I should have read the code in `op_init_update_refs`, it doesn't change GC state, we can remove the the call of `propagate_gc_state_to_all_threads` to clean up code a little bit, it was missed when you replaced the init_update_refs pause with handshake.

For `final_roots`, I think I should leave it as it is in this PR, later you will remove the timings and gc state propagation into a handshake anyway.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23759#discussion_r1970708588