RFR: 8210233: Prepare Klass::is_loader_alive() for concurrent class unloading

[Kim Barrett]

> On Aug 30, 2018, at 2:56 PM, Erik Österlund <erik.osterlund at oracle.com> wrote:
> 
> Hi,
> 
> The Klass::is_loader_alive() facility currently assumes that CLDs are set to unloading before giving a correct answer. This is a problem for concurrent class unloading. This needs to instead be evaluated in a more concurrency friendly fashion, so that it will give the right answer even in concurrent contexts.
> 
> The proposed solution is to stop using the cached unloading value, and instead ask the CLD if it is_alive(), which utilizes a phantom load on the CLD holder, and is concurrency friendly.
> 
> Webrev:
> http://cr.openjdk.java.net/~eosterlund/8210233/webrev.00/
> 
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8210233
> 
> Thanks,
> /Erik

Nearby comments involving "unloading" should be updated.