RFR (M): 8159984: Remove call to ClassLoaderDataGraph::clear_claimed_marks during the initial mark pause

[Thomas Schatzl]

Hi Kim,

   thanks for your review.

On 18.09.19 20:36, Kim Barrett wrote:
>> On Sep 18, 2019, at 11:22 AM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
>>
>> Hi all,
>>
>>   can I have reviews for this change that, given the observation that during root processing, there is only one kind of root that walks CLDs, we do not need to
>>
>> [...]
>>
>> (based on JDK-8231117)
>>
>> Thanks,
>>   Thomas
> 
> I was just looking at the root scanning code recently, trying to
> figure out what worker_has_discovered_all_strong_classes() was about.
> 
> The naming of worker_has_discovered_all_strong_classes() and
> wait_until_all_strong_classes_discovered() seems wrong now.  These are
> about discovering/processing strong nmethods now.
> 
> A better comment at the call to the wait function about why it's
> called there would be helpful.  Obviously we want it as late as
> possible, to allow threads to get past the notification.  But why not
> later?  

We could at the latest do the waiting when we do the nmethod weak root 
scanning. Given that I think I now have a working prototype that works 
without the barrier I did not care optimizing that for this change.
If there are any unforeseen issues, or it does not pan out, I can 
improve that (in a separate CR if needed).

I fixed the naming of the two methods and tried to improve the comment 
in a new webrev.

New webrevs:
http://cr.openjdk.java.net/~tschatzl/8159984/webrev.0_to_1/ (diff)
http://cr.openjdk.java.net/~tschatzl/8159984/webrev.1/ (full)

> (We talked about this off-line; this is just a reminder and
> request for some commentary capturing that discussion. Though
> hopefully your idea for getting rid of the barrier completly will pan
> out.
> 
> Other than that, looks good.
> 

Thanks!

Thomas