RFR: 8315373: Change VirtualThread to unmount after freezing, re-mount before thawing

[Markus Grönlund]

On Fri, 1 Sep 2023 11:26:48 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Ok. If the thread can run native code as part of the mount / unmount, and the sampler can see the intermediary state there too, the check is needed.
>
> Thanks. One other thing that I see when more testing with generational ZGC is that ZPageAllocator::alloc_page will record an event and this can happen during a mount transition. So I think JfrStackTrace::record also needs to test if the current thread is a virtual thread without a continuation mounted.

That is not good. Such a check would be attributed to all event sites, making them all slower.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15492#discussion_r1312915249