JFR emergency dump didn't happen at OOM

[Yasumasa Suenaga]

Hi Erik,

I filed this to JBS, and I've sent PR:
   https://github.com/openjdk/jdk/pull/26468

I hope this issue will be fixed soon :)


Thanks,

Yasumasa


On 2025/07/25 2:45, Erik Gahlin wrote:
> Hi Yasumasa,
> 
> This looks more reasonable, although most of it is a refactoring.
> 
> Could you turn it into a PR with a webrev so it's easier to review?
> 
> Thanks
> Erik
> 
> 
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> *From:* hotspot-jfr-dev <hotspot-jfr-dev-retn at openjdk.org> on behalf of Yasumasa Suenaga <suenaga at oss.nttdata.com>
> *Sent:* Thursday, July 24, 2025 11:21 AM
> *To:* hotspot-jfr-dev at openjdk.org <hotspot-jfr-dev at openjdk.org>
> *Subject:* JFR emergency dump didn't happen at OOM
> Hi all,
> 
> I reported and proposed the fix about 6 years ago (!), I faced the issue again that would be helpful if this is fixed.
> 
> 6 years ago, we discussed about this issue in [1], then I hear JDK-8196050 might fix this issue, but it hasn't yet happened unfortunately...
> 
> JDK codebase has been made a lot of changes in 6 years, so I think we can fix simply than I proposed before.
> All of changes is [2]. It is not so big change and it is good because no flags are added in .jfc files. What do you think? I will send PR if it is ok, but I want to hear your opinions before PR (because we discussed before).
> 
> For example, we can pass a flag for OOM rather than exception handler as following:
> 
> ```
> --- a/src/hotspot/share/jfr/recorder/repository/jfrEmergencyDump.cpp
> +++ b/src/hotspot/share/jfr/recorder/repository/jfrEmergencyDump.cpp
> @@ -556,22 +556,21 @@ class JavaThreadInVMAndNative : public StackObj {
>      }
>    };
> 
> -static void post_events(bool exception_handler, Thread* thread) {
> -  if (exception_handler) {
> +static void post_events(bool is_oom, Thread* thread) {
> +  if (is_oom) {
> +    LeakProfiler::emit_events(max_jlong, false, false);
> +  } else {
>        EventShutdown e;
>        e.set_reason("VM Error");
>        e.commit();
> -  } else {
> -    // OOM
> -    LeakProfiler::emit_events(max_jlong, false, false);
>      }
>      EventDumpReason event;
> -  event.set_reason(exception_handler ? "Crash" : "Out of Memory");
> +  event.set_reason(is_oom ? "Out of Memory" : "Crash");
>      event.set_recordingId(-1);
>      event.commit();
>    }
> ```
> 
> And also we can identify whether OOM or not (crash) via `id` in argument of `report_and_die`:
> ```
> --- a/src/hotspot/share/utilities/vmError.cpp
> +++ b/src/hotspot/share/utilities/vmError.cpp
> @@ -1856,7 +1856,7 @@ void VMError::report_and_die(int id, const char* message, const char* detail_fmt
>        log.set_fd(-1);
>      }
> 
> -  JFR_ONLY(Jfr::on_vm_shutdown(true);)
> +  JFR_ONLY(Jfr::on_vm_shutdown(static_cast<VMErrorType>(_id) == OOM_JAVA_HEAP_FATAL);)
> 
> ```
> 
> 
> Thanks,
> 
> Yasumasa
> 
> 
> [1] https://mail.openjdk.org/pipermail/hotspot-jfr-dev/2019-January/000381.html <https://mail.openjdk.org/pipermail/hotspot-jfr-dev/2019-January/000381.html>
> [2] https://github.com/YaSuenag/jdk/commit/3f18fd74679387c385a8f79c8bea5b6b1f2815c0 <https://github.com/YaSuenag/jdk/commit/3f18fd74679387c385a8f79c8bea5b6b1f2815c0>