RFR: 8272611: Use parallel heap inspection when print classhisto info in gc log

[Thomas Schatzl]

On Fri, 27 Aug 2021 09:07:07 GMT, Bin Liao <github.com+3094961+buddyliao at openjdk.org> wrote:

>> Note: this is probably copy&pasted from `ClassHistogramDCmd::execute`; instead of the copy&paste please at least add something like a static `default_parallel_thread_num()` method to `VM_GC_HeapInspection`.
>
>> Where do the magic numbers for the formula come from? Please consider using the ergonomically determined number of threads (`CollectedHeap::safepoint_workers()->active_workers()`)? (Maybe change this in another CR as other reviewers think is better, looking whether there is a significant difference between these numbers)
> 
> Thank you for your advice, it seems that (CollectedHeap::safepoint_workers()->active_workers()) looks better.

👍

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PR: https://git.openjdk.java.net/jdk/pull/5158