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

Kim Barrett kim.barrett at oracle.com
Thu Sep 19 17:27:20 UTC 2019

> On Sep 19, 2019, at 5:42 AM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 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)

The additional comments look good.  But shouldn’t the names of those functions refer to “nmethods"
rather than (generic) “roots”?  That is,


There are certainly strong roots that get looked at after the has_discovered call.

>> (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

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