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

[David Holmes]

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?

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
>