RFR: 8359110: Log accumulated GC and process CPU time upon VM exit [v9]

[Stefan Karlsson]

On Mon, 23 Jun 2025 14:17:05 GMT, Jonas Norlinder <duke at openjdk.org> wrote:

>> src/hotspot/share/gc/shared/collectedHeap.hpp line 245:
>> 
>>> 243: 
>>> 244:   // Stop any onging concurrent work and prepare for exit.
>>> 245:   virtual void stop();
>> 
>> I find it a bit odd to call `log_gc_vtime` inside this method, given the comment and its name. I wonder if `print_tracing_info` can be used instead, which is invoked before exit as well.
>
> I think it makes sense. We want to log the total GC CPU time before exiting. The latest point we can do that is right before we terminate threads, which we do in when we call `ConcurrentGCThread::stop`. I am open for any suggestions to rename `log_gc_vtime` in case that would help.

I'd also prefer to see a small adjustment here. With this change all GCs have to add a back call to `CollectedHeap::stop()`. I think it makes the could a tiny bit less clean.

I wonder if an alternative could be to split `CollectedHeap::stop()` into two functions:

virtual void CollectedHeap::stop() = 0; // Now pure virtual

void CollectedHeap::before_exit() {
  // Log GC CPU usage.
  log_gc_vtime();

  // Stop any on-going concurrent work and prepare for exit.
  stop();
}

And revert the added calls to `CollectedHeap::stop()`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25779#discussion_r2162341225