RFR (M) 8210155: Lock ClassLoaderDataGraph

[Erik Osterlund]

Hi Coleen,

This looks good to me. I cherry picked this into my concurrent class unloading branch (and added the new lock around do_unloading). It passed GC test suite unloading and deleting classes concurrently, and also scanning the CLD roots concurrently. So that seems all good.

Thanks for making this code more concurrency friendly.

Thanks,
/Erik

> On 29 Aug 2018, at 18:07, coleen.phillimore at oracle.com wrote:
> 
> Summary: In preparation for concurrent class unloading.
> 
> open webrev at http://cr.openjdk.java.net/~coleenp/8210155.01/webrev
> bug link https://bugs.openjdk.java.net/browse/JDK-8210155
> 
> Tested with mach5 hs-tier1-7, which tests JFR and JVMTI changes. Also tested with performance dev-submit testing with no regression.
> 
> Thanks,
> Coleen