RFR: 8199925: Break out GC selection logic from GCArguments to GCSelector

[Erik Österlund]

Hi Per,

I like this. Looks good.

Thanks,
/Erik

On 2018-03-21 14:11, Per Liden wrote:
> Hi,
>
> Here's an updated webrev. I renamed GCSelector to GCConfig and it's 
> now also the goto place for getting hold of the GCArguments instance 
> for the currently selected GC.
>
> http://cr.openjdk.java.net/~pliden/8199925/webrev.1
>
> Btw, this is built on top of JDK-8199850 (Move parsing of VerifyGCType 
> to G1) and JDK-8199918 (Shorten names of CollectedHeap::Name members), 
> and the GCConfig::is_gc_* functions will eventually be used by 
> JDK-8199927 (Make WhiteBox more GC agnostic).
>
> /Per
>
> On 03/21/2018 11:33 AM, Per Liden wrote:
>> Hi Roman,
>>
>> On 03/21/2018 10:15 AM, Roman Kennke wrote:
>>> Am 21.03.2018 um 09:12 schrieb Per Liden:
>>>> In an attempt to make WhiteBox more GC agnostic, and in turn make it
>>>> easier to plugin new GC without touching a lot of non-GC code, this
>>>> patch breaks out the GC selection logic from GCArguments to 
>>>> GCSelector.
>>>> There are two reasons why I think this makes sense:
>>>> 1) The GC selection logic is self-contained and fairly unrelated to 
>>>> the
>>>> rest of the flags processing done by GCArguments and its GC-specific
>>>> children.
>>>> 2) Parts of the GC selection logic is needed by WhiteBox to answer
>>>> questions about which GC are supported, selected, etc.
>>>>
>>>> A follow up patch (JDK-8199927) will change WhiteBox (WB_CurrentGC,
>>>> WB_AllSupportedGC, WB_GCSelectedByErgo), to use the GCSelector.
>>>>
>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8199925
>>>> Webrev: http://cr.openjdk.java.net/~pliden/8199925/webrev.0
>>>>
>>>> /Per
>>>
>>> My original proposal for the GCArguments did have a separate 
>>> GCFactory. :-)
>>>
>>> In generally I like your change.
>>>
>>> I'd probably go even further and let GCSelector initialize and 
>>> return an
>>> instance of GCArguments. This way we wouldn't end up with two places
>>> that have knowledge of all possible GCs, but would only have one place
>>> (GCSelector) where one had to hook up for adding a new GC.
>>>
>>> What do you think?
>>
>> My intention here was that GCSelector would be a pure translator of 
>> Use*GC flags to CollectedHeap::Name, i.e. a small and well defined 
>> component, which knows nothing about GCArguments. The purpose of this 
>> was to clean out the WhiteBox stuff.
>>
>> On the other hand, I see what you mean, and too would like to reach a 
>> state where we have one place in the code that "knows about all the 
>> GCs".
>>
>> Let me think about it some more and maybe prototype an alternative, 
>> and we'll see if that gets us to a better place.
>>
>> /Per
>>
>>>
>>> Roman
>>>