Make +UseZGC fail hard when it is unsupported

[Aleksey Shipilev]

On 06/14/2018 05:58 PM, Per Liden wrote:
> Hi Aleksey,
> 
> On 06/14/2018 10:59 AM, Aleksey Shipilev wrote:
>> On 06/14/2018 10:55 AM, Per Liden wrote:
>>> On 06/14/2018 10:45 AM, Aleksey Shipilev wrote:
>>>> I have build recent workspace, and forgot to enable zgc in configure. Yet, the runs proceeded as
>>>> usual, and G1 was automatically selected. Per, can you make this failure fatal?
>>>
>>> This behavior is in line with how this mechanism works for all other GCs, so it's not ZGC specific.
>>> E.g. if you build a minimal VM you should see the same behavior if you try to enable, say G1.
>>>
>>> However, it can certainly be debated whether this is a good behavior or not, and I tend to agree
>>> with you that it's not.
>>
>> Sure. My point was that users would become exposed to this with optionally-compiled experimental GC
>> very often now. Hardly anyone uses minimal VM, but everyone would use server VM with optional GCs.
>> Would be sad to see reports against ZGC, Shenandoah, Epsilon that are not actually running those GCs.
>>
>> Since you were redoing the gcConfig machinery, would you have cycles to make RFE that makes this
>> warning fatal?
> 
> Sure, I'll look into it.

Thank you!

-Aleksey