RFR: 8203923: Add @requires feature to check flag values for the running JVM

[Kim Barrett]

> On May 29, 2018, at 10:21 AM, Stefan Karlsson <stefan.karlsson at oracle.com> wrote:
> 
> Hi all,
> 
> Please review this patch to add @requires vm.opt.final.<vm flag name>, as a way to filter jtreg tests on the final value of flags in the test VM.
> 
> http://cr.openjdk.java.net/~stefank/8203923/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8203923
> 
> This patch is needed to allow tests to be filtered out when ZGC is run.
> 
> ZGC doesn't support UseCompressedOops (and currently doesn't support ClassUnloading). Instead of adding @requires vm.gc != "Z" for tests that rely on ClassUnloading, I think it's nicer to write @requires vm.opt.final.ClassUnloading.
> 
> This will filter out the test if any of the following conditions are met:
> 1) The currently executing VM doesn't support ClassUnloading
> 2) -XX:-ClassUnloading is passed to the test
> 
> The second case can today be handled by @requires vm.opt.ClassUnloading == NULL | vm.opt.ClassUnloading == true, or maybe simpler @requires vm.opt.ClassUnloading != false, but if you need both @requires vm.opt.final.ClassUnloading should be used.
> 
> The current solution requires the queried flags to be listed in vmOptFinalFlags. Maybe there's a way to get this to cover all flags automatically?
> 
> Thanks,
> StefanK

Looks good.