RFR: 8252105: parallel heap inspection for ZCollectedHeap

[Per Lidén]

On Thu, 10 Sep 2020 02:28:43 GMT, Lin Zang <lzang at openjdk.org> wrote:

> - enable parallel heap inspection for ZCollectedHeap
> - preliminary evaluation:
>   Time of jmap histo on 8GB heap with ~5GB objects
>   * before: 7.103s
>   * after : 2.734s (with 4 parallel threads)

Just looked at this briefly. My initial comment is that we need to avoid all the code duplicated from ZHeapIterator and
isolate all this a bit better. Perhaps folding everything into one iterator, that can be used by both object_iterate()
and parallel_object_iterator(). I'll take a closer look, and perhaps try some alternatives, when I get a chance.

-------------

PR: https://git.openjdk.java.net/jdk/pull/103