RFR: 8284828: Use `os::ThreadCrashProtection` to protect AsyncGetCallTrace from crashing [v9]

[Thomas Stuefe]

On Thu, 14 Apr 2022 17:08:32 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

> For additional context, I should add that the CrashProtection mechanism was mainly put in place as a result of having to deliver JFR from JRockit into Hotspot under a deadline, upholding feature-parity. The stack walking code was in really bad shape back then. Over the years, it has been hardened and improved much, and I have not seen any reported issues about JFR crashes in many years (we log when crashing in production).
> 
> An important difference is that AGCT allows more thread states compared to JFR, so there can be issues in that area that are not seen in JFR.

Thanks for the JFR insight, Marcus. I can see the CrashProtection being a stop-gap measure under time constraints. Maybe worth rethinking now. From your description, the way it is used in JFR differ significantly from how the async-profiler would use it.

Privately, I start wondering whether the benefits of async-profiler over JFR are worth the risk of corrupting the VM or the work needed to harden out AGCT. Their feature-set seems to overlap a lot. I may not see the whole picture though, I'm not a profiler expert.

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PR: https://git.openjdk.java.net/jdk/pull/8225