RFR(S): 8068579: Running with -XX:-UseParallelGC does not turn ParalleGC off

[Bengt Rutisson]

Hi Per,

On 2016-03-17 14:36, Per Liden wrote:
> Hi,
>
> On 2016-03-16 09:12, Per Liden wrote:
>> Hi Dima,
>>
>> On 2016-03-15 17:38, Dmitry Fazunenko wrote:
>>> Hi Per,
>>>
>>> A couple of comments:
>>> 1) globals_extension.hpp.frames.html
>>> requires copyright update
>>> 2) such fix should go with a regression test, it could be done
>>> separately.
>>
>> Good point. I was about to add a test for this just now and realized
>> that the new semantics is not kept for minimal VMs (i.e. when
>> INCLUDE_ALL_GCS==0). I'll rework the patch a bit to have the same
>> semantics also on minimal VMs. New webrev coming.
>
> Here's an updated webrev. The new semantics is now available on all 
> VMs (including minimal). I also added a new test for this.
>
> This change also removes UNSUPPORTED_GC_OPTION() and instead reuses 
> the existing UNSUPPORTED_OPTION(), which I tweaked slightly to make 
> the output more consistent across the code base. This in turn meant 
> that I needed to adjust some other tests.
>
> http://cr.openjdk.java.net/~pliden/8068579/webrev.1/

I think this looks good but I think I would prefer to split the changes 
up into two separate changes. One for the general UNSUPPORTED_OPTION() 
support (that affects the compiler tests etc) and one for the GC default 
selection.

Overall a very nice cleanup. Thanks for doing this!

Bengt

>
> Testing: jprt, manual
>
> thanks,
> Per
>
>>
>> thanks,
>> Per
>>
>>>
>>> Thanks,
>>> Dima
>>>
>>>
>>> On 15.03.2016 16:48, Per Liden wrote:
>>>> Summary: Explicitly disabling the default collector, without
>>>> specifying another collector, will silently re-enable the default
>>>> collector. This is a bit counter intuitive. A better approach would be
>>>> for the VM to complain about the situation.
>>>>
>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8068579
>>>> Webrev: http://cr.openjdk.java.net/~pliden/8068579/webrev.0/
>>>> Testing: manual, jprt
>>>>
>>>> Example (assuming it's a platform/configuration with G1 as default):
>>>>
>>>> $ java -XX:-UseG1GC ...
>>>>
>>>> Today, the above command will happily start a VM with G1 enabled.
>>>>
>>>> With this patch the VM will instead complain, like this:
>>>>
>>>> $ java -XX:-UseG1GC ...
>>>> Error occurred during initialization of VM
>>>> Garbage collector not selected (default collector explicitly disabled)
>>>>
>>>> And of course, we're good with disabling the default collector as long
>>>> as you specify some other collector, e.g.:
>>>>
>>>> $ java -XX:-UseG1GC -XX:+UseParallelGC ...
>>>>
>>>> cheers,
>>>> Per
>>>