RFR: 8199927: Make WhiteBox more GC agnostic

[Per Liden]

On 03/21/2018 04:03 PM, Aleksey Shipilev wrote:
> On 03/21/2018 03:50 PM, Per Liden wrote:
>> Updated webrev to reflect that GCSelector changed name to GCConfig in the patch for JDK-8199925.
>>
>> http://cr.openjdk.java.net/~pliden/8199927/webrev.1
> 
> Looks good to me.

Thanks for reviewing!

> 
> This is a little dizzy, because I would have expected gc.isSelected() would tell me exactly what GC
> was being selected:
> 
>   isAcceptable = gc.isSupported() && (gc.isSelected() || GC.isSelectedErgonomically());
> 
> ...so it should be just:
> 
>   for (GC gc : GC.values()) {
>     map.put("vm.gc." + gc.name(), "" + gc.isSelected());
>   }
> 

The way VMProps works and how the properties are set up can indeed make 
you a little dizzy. For example, vm.gc.Parallel=true doesn't necessarily 
mean that ParallelGC was "selected", just that it's an "acceptable" 
configuration.

A test running with an explicit -XX:UseG1GC flag will get:
vm.gc.Serial=false
vm.gc.Parallel=false
vm.gc.CMS=false
vm.gc.G1=true

And a test running with no explicit GC flag (which selects G1 
ergonomically), will get:
vm.gc.Serial=true
vm.gc.Parallel=true
vm.gc.CMS=true
vm.gc.G1=true

I believe your suggested cleanup would change that behavior.

cheers,
Per

> ?
> 
> Thanks,
> -Aleksey
>