RFR: 8254562: ZGC: Remove ZMarkRootsTask [v3]

[Stefan Karlsson]

On Mon, 12 Oct 2020 16:15:38 GMT, Per Liden <pliden at openjdk.org> wrote:

>> Stefan Karlsson has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Review 1
>
> src/hotspot/share/gc/z/zRelocate.cpp line 72:
> 
>> 70:     // During relocation we need to visit the JVMTI
>> 71:     // export weak roots to rehash the JVMTI tag map
>> 72:     ZRelocateRoots::oops_do(&_cl);
> 
> I would have been more explicit here, something like this:
> 
> class ZRelocateJVMTIWeakExportTask : public ZTask {
> public:
>   ZRelocateJVMTIWeakExportTask() :
>       ZTask("ZRelocateJVMTIWeakExportTask") {}
> 
>   virtual void work() {
>     AlwaysTrueClosure always_alive;
>     ZRelocateRootsIteratorClosure _cl;
>     JvmtiExport::weak_oops_do(&always_alive, &cl);
>   }
> };
> 
> void ZRelocate::start() {
>   // During relocation we need to visit the JVMTI
>   // export weak roots to rehash the JVMTI tag map
>   ZStatTimer timer(ZSubPhasePauseRelocateJVMTIWeakExport);
>   ZRelocateJVMTIWeakExportTask task;
>   _workers->run_serial(&task);
> }
> 
> But this code will go away soon anyway, so you decide.

I agree, and I actually started that way, but hit some minor snags that ZSubPhasePauseRelocateJVMTIWeakExport wasn't
available to zRelocate.cpp, and I wasn't sure about moving a *PhasePause* instance out from the zRootsIterator.cpp.

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PR: https://git.openjdk.java.net/jdk/pull/601