RFR (S) JDK-8162553: Crash in class unloading due to null CLD having a zero _keep_alive value

[David Holmes]

On 10/08/2016 8:09 AM, Lois Foltan wrote:
>
> On 8/9/2016 5:57 PM, Karen Kinnear wrote:
>> Code looks good. Agree with David about comment about use - for the
>> _keep_alive field: for
>> loaders never unloaded (boot now, platform and application I would
>> expect us to add), and for
>> anonymous classes via reference count methods.
>
> Thank you Karen for the review.  I have improved upon the comments as
> requested.
>
> Updated webrev at:
>     http://cr.openjdk.java.net/~lfoltan/bug_jdk8162553.1/webrev/

Looks ok.

Thanks,
David

> Lois
>
>>
>> thanks,
>> Karen
>>
>>> On Aug 8, 2016, at 3:41 PM, Lois Foltan <lois.foltan at oracle.com> wrote:
>>>
>>> Hello,
>>>
>>> Please review the following fix:
>>>
>>> Webrev:
>>> http://cr.openjdk.java.net/~lfoltan/bug_jdk8162553/webrev/
>>>
>>> Bug: Crash in class unloading due to null CLD having a zero
>>> _keep_alive value
>>> https://bugs.openjdk.java.net/browse/JDK-8162553
>>>
>>> Summary:
>>> Limit the increment/decrement of the ClassLoaderData _keep_alive
>>> field to just ClassLoaderData(s) created specifically for an
>>> anonymous class.  Due to the uniqueness that no other class shares an
>>> anonymous class' ClassLoaderData, no other non-GC thread has
>>> knowledge of the anonymous class while it is being defined.  By
>>> limiting the increment/decrement to just ClassLoaderData(s) dedicated
>>> to anonymous classes, the need to make this an atomic operation is
>>> avoided.  This bug was exposed since java_lang_Class::create_mirror()
>>> is multi-threaded once java.lang.Class is loaded during JVM start up.
>>>
>>> Testing:
>>> Several runs of hotspot nightly testing and several iterations of
>>> various tests that have exposed this issue.
>>>
>>> Thanks,
>>> Lois
>