RFR: add parallel heap inspection support for jmap histo(G1)

[David Holmes]

Hi Lin,

Adding in hotspot-gc-dev as they need to see how this interacts with GC 
worker threads, and whether it needs to be extended beyond G1.

I happened to spot one nit when browsing:

src/hotspot/share/gc/shared/collectedHeap.hpp

+   virtual bool run_par_heap_inspect_task(KlassInfoTable* cit,
+                                          BoolObjectClosure* filter,
+                                          size_t* missed_count,
+                                          size_t thread_num) {
+     return NULL;

s/NULL/false/

Cheers,
David

On 18/02/2020 2:15 pm, linzang(臧琳) wrote:
> Dear All,
>       May I ask your help to review the follow changes:
>       webrev: 
> http://cr.openjdk.java.net/~lzang/jmap-8214535/8215264/webrev_00/
>       bug: https://bugs.openjdk.java.net/browse/JDK-8215624
>       related CSR: https://bugs.openjdk.java.net/browse/JDK-8239290
>       This patch enable parallel heap inspection of G1 for jmap histo.
>       my simple test shown it can speed up 2x of jmap -histo with 
> parallelThreadNum set to 2 for heap at ~500M on 4-core platform.
> 
> ------------------------------------------------------------------------
> BRs,
> Lin