RFR: 8307348 - Parallelize heap walk for ObjectCount(AfterGC) JFR event collection [v5]

[Aleksey Shipilev]

On Fri, 5 May 2023 11:46:28 GMT, olivergillespie <duke at openjdk.org> wrote:

>> src/hotspot/share/gc/shared/gcVMOperations.cpp line 174:
>> 
>>> 172:       // Can't run with more threads than provided by the WorkerThreads.
>>> 173:       const uint capped_parallel_thread_num = MIN2(_parallel_thread_num, workers->max_workers());
>>> 174:       WithActiveWorkers with_active_workers(workers, capped_parallel_thread_num);
>> 
>> `WithActiveWorkers` is an stack-obj, so it must be in the same scope as using workers.
>
> Oh, good catch. So can I do something like:
> 
> 
> HeapInspection inspect;
> if (workers != nullptr) {
>     // The GC provided a WorkerThreads to be used during a safepoint.
>     // Can't run with more threads than provided by the WorkerThreads.
>     const uint capped_parallel_thread_num = MIN2(_parallel_thread_num, workers->max_workers());
>     WithActiveWorkers with_active_workers(workers, capped_parallel_thread_num);
>     inspect.heap_inspection(_out, workers);
> } else {
>     inspect.heap_inspection(_out, nullptr);
> }
> 
> 
> ?
> 
> (I'm not familiar with the exact workings of StackObj, sorry)

Yes, do that.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13774#discussion_r1186020045