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

[Per Liden]

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/

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
>>