RFR: 8279016: JFR Leak Profiler is broken with Shenandoah

[Aleksey Shipilev]

On Fri, 26 Jul 2024 11:40:51 GMT, Erik Gahlin <egahlin at openjdk.org> wrote:

>> I agree using `sleep` here is not great. But I could not find a better way to do it.
>> 
>> When I was looking at this test, I noticed that `OldObjectSample` event is only emitted when recording is stopped: https://github.com/openjdk/jdk/blob/7f11935461a6ff1ef0fac800fb4264a519e21061/src/jdk.jfr/share/classes/jdk/jfr/internal/OldObjectSample.java#L41-L42 -- this is why I thought to add `sleep` right before we stop the recording.
>> 
>> So going async does not really help, because of this circularity: we only stop the recording when event is received, which we would not receive until recording is stopped. Sure enough, this times out:
>> 
>> 
>>     public static void main(String[] args) throws Exception {
>>         WhiteBox.setWriteAllObjectSamples(true);
>> 
>>         try (RecordingStream rs = new RecordingStream()) {
>>             rs.enable(EventNames.OldObjectSample).withoutStackTrace().with("cutoff", "infinity");
>>             rs.onEvent(e -> {
>>                 try {
>>                     if (hasValidField(e)) {
>>                         rs.close();
>>                     }
>>                 } catch (Exception ex) {
>>                     ex.printStackTrace();
>>                 }
>>             });
>> 
>>             rs.startAsync();
>>             addToTestField();
>>             rs.awaitTermination();
>>         }
>>     }
>
> I see the problem now. 
> 
> As I understand it, this only happens with Shenandoah. Would it be possible to sleep only when using that GC? Or perhaps repeat on failure, increasing the sleep time with a few seconds för every iteration, starting with 0s?

Sure, I can try that. I would not like to specialize the test for Shenandoah, but retries with backoffs sound fine.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20328#discussion_r1692956428