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

[Lois Foltan]

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/

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