RFR 8038212: Method::is_valid_method() check has performance regression impact for stackwalking

[Mikael Gerdin]

Hi Coleen,

On Monday 12 May 2014 20.19.15 Coleen Phillimore wrote:
> Summary: Only prune metaspace virtual spaces at safepoint so walking
> them is safe outside a safepoint.
> 
> Walking class loader data graph for contains is really slow for
> applications like nashorn that has a lot of class loader data.
> 
> Tested with nsk.quick.testlist, jtreg tests, and jck tests.  Also ran
> 
> open webrev at http://cr.openjdk.java.net/~coleenp/8038212/
> bug link https://bugs.openjdk.java.net/browse/JDK-8038212

Thanks for taking care of this fix.
I think the idea of deferring CLDG::purge to the next safepoint cleanup is 
sound.

I like the removal of CLDG::contains since it makes more sense to ask 
Metaspace straight up.

I have a small question about the test you added:

3798   static void test_contains() {
3799     // Test that all the methods in the CLDG are contained
3800     ClassLoaderDataGraph::methods_do(assert_contains);
3801   }

Have we always allocated methods at this point in the VM startup?

Should we also test CLDG::classes_do to make sure it works for the compressed 
class space?

/Mikael

> 
> Marcus L. tested it with nashorn tests.
> 
> Thanks,
> Coleen