RFR: 8256382: Use try_lock for hs_err EventLog printing

[David Holmes]

On Tue, 24 Nov 2020 14:45:59 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Hi Stefan,
>> 
>> can't we just print out unconditionally if VMError::is_error_reported()? Whats the worst that can happen, we crash? Then we would continue with the next reporting step. But we still have a chance to see the event buffer contents even if the event logger itself crashed or asserted.
>> 
>> Side note, some time ago I rewrote the whole event system: https://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2019-March/033150.html to a much simpler implementation and I think that one would also be pretty safe to get printed even if unlocked since it works on a static pre-allocated buffer. But that work somehow got bogged down in review and I never got around to drive it upstream. If there is enough interest I may take up the work again.
>
> Hi @tstuefe 
> 
> With your proposal, if we have a section that looks like this:
> * event log instance 0
> * event log instance 1
> * event log instance 2
> * other type of printing
> 
> and we crash at "event log instance 1", then we completely skip printing "event log instance 2" and "other type of printing". My thinking was that that was unfortunate, and I wanted to localize the problem. We often have this problem that one hs_err crash hides important information that was supposed to be written later, because a lot of the code in the hs_err printing isn't hardened and the hs_err sections are on a too high level (IMHO).
> 
> With that said, I don't mind skipping the trying to take the lock if we are printing the hs_err file. Do others agree with Thomas?

Don't we have to check not only VMError::is_error_reported, but that it is the current thread that is doing the reporting?

I also think the Thread::current_or_null()==NULL case has to mean we are doing the error reporting very early in VM init - else how can we get in here in a "non attached" thread? Even then I'm not sure that is actually possible either - at what point in VM init have we installed our crash handler?

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PR: https://git.openjdk.java.net/jdk/pull/1408