RFR: 8336299: Improve GCLocker stall diagnostics [v5]

[Aleksey Shipilev]

On Mon, 12 Aug 2024 07:59:17 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Neethu Prasad has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   address code style feedback
>
> src/hotspot/share/gc/shared/gcLocker.cpp line 139:
> 
>> 137:   // Wait for _needs_gc  to be cleared
>> 138:   while (needs_gc()) {
>> 139:     GCLockerTimingDebugLogger logger("Thread stalled by JNI critical section.");
> 
> If a spurious wakeup occurs, the logger will be instantiated multiple times, this can lead to confusing log msgs, right? If so, I wonder whether it makes sense to extract `logger` out of the while-iteration.

Agreed. Same in `GCLocker::jni_lock` below.

It would probably take the form of:


if (needs_gc()) {
  GCLockerTracer::inc_stall_count();
  log_debug_jni("Allocation failed. Thread stalled by JNI critical section.");
  GCLockerTimingDebugLogger logger("Thread stalled by JNI critical section.");
  while (needs_gc()) {
    ml.wait();
  }
}

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PR Review Comment: https://git.openjdk.org/jdk/pull/20277#discussion_r1713459073