RFR: 8359820: Improve handshake/safepoint timeout diagnostic messages [v3]

[Thomas Stuefe]

On Fri, 18 Jul 2025 09:09:39 GMT, David Holmes <dholmes at openjdk.org> wrote:

> > I have nothing against making this clearer, just saying that the info is already kind of there.
> 
> Yes, but there are a few reasons a SIGILL may have been fired at a thread, so it would be useful to get a clear indication of exactly why it happened. Not everyone will realize/know that SIGILL happens because of a timeout in handshake/safepoint.

I still don't get it.

- Is the receiving thread the one meant to receive the SIGILL? Then why print this at all, we have callstack and thread info already?
- Is the receiving thread not the originally intended recipient? But how? This can only happen either if the original recipient thread blocked - which we don't do in hotspot code AFAIK, so it could only be a library method that temporary sets a signal mask - or if there is a bug in the sending code - in which case we should fix it?
- Is the SIGILL completely unrelated to the safepoint? Then why print the information?

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PR Comment: https://git.openjdk.org/jdk/pull/26309#issuecomment-3088856848