RFR(xs): 8203455: jcmd: VM.metaspace: print loader name for anonymous CLDs.

[Thomas Stüfe]

Hi David,

On Mon, May 21, 2018 at 4:23 AM, David Holmes <david.holmes at oracle.com> wrote:
> Hi Thomas,
>
> There's been a bit of discussion lately about how to "describe"
> classloaders:
>
> https://bugs.openjdk.java.net/browse/JDK-8202605
>
> I'd rather not see another chunk of code added that 8202605 will have to fix
> up. Can you live with the less-than-ideal output of the existing function,
> under the expectation it will be updated to do a better job in the future?
>

8206205 does not alleviate the need for this change, since currently
we do not print any loader information for anonymous classes.
Originally I planned to fix up this patch with a follow up patch later
once those utility functions are in place in ClassloaderData.

But yes, I can save us some review work by waiting a bit and then
doing only one change. Lets hope it does not take too long, I have
more changes coming up which print class loader names.

So I retract this RFR for now and will repost another patch once
8206205 is done.

Thanks, Thomas

> Thanks,
> David
>
>
> On 20/05/2018 4:49 PM, Thomas Stüfe wrote:
>>
>> Hi all,
>>
>> may I please have reviews for this small addition.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8203455
>> Webrev:
>> http://cr.openjdk.java.net/~stuefe/webrevs/8203455-VM.metaspace-display-loader-name-for-anonymous-cld/webrev.00/webrev/
>>
>> VM.metaspace show-loaders can be used to display loaders (well, really
>> CLD instances).
>>
>> For anonymous CLDs, only "anonymous" is shown. It would be helpful to
>> show to which loader these CLD are assigned.
>>
>> Before:
>>
>>   "272: ClassLoaderData 0x00007f5ba0538f10 for anonymous class"
>>
>>
>> http://cr.openjdk.java.net/~stuefe/webrevs/8203455-VM.metaspace-display-loader-name-for-anonymous-cld/example-before.txt
>>
>> After patch:
>>
>>   "268: CLD 0x00007ff0c45738f0 for <anonymous class>, loaded by app,
>> instance of jdk.internal.loader.ClassLoaders$AppClassLoader"
>>
>>
>> http://cr.openjdk.java.net/~stuefe/webrevs/8203455-VM.metaspace-display-loader-name-for-anonymous-cld/example-after.txt
>>
>> --
>> Notes: this patch has a bit more lines than I liked because I did not
>> find a singly utility function in ClassloaderData which fit my
>> purpose. I wanted to see name and class of the associated loader for
>> both normal and unloading case. ClassloaderData::loader_name() has a
>> number of shortcomings, I opened
>> https://bugs.openjdk.java.net/browse/JDK-8203456 as a follow up rfe.
>>
>> Thank you,
>>
>> Thomas
>>
>