RFR 8055008: Clean up code that saves the previous versions of redefined classes

[Coleen Phillimore]

On 8/20/14, 6:45 PM, Daniel D. Daugherty wrote:
> On 8/20/14 2:01 PM, Coleen Phillimore wrote:
>> On 8/20/14, 3:49 PM, serguei.spitsyn at oracle.com wrote:
>>>>
>>>> If an EMCP method is not running, should we save it on a previous 
>>>> version list anyway so that we can make it obsolete if it's 
>>>> redefined and made obsolete?
>>>
>>> I hope, Dan will catch me if I'm wrong...
>>>
>>> I think, we should not.
>>> An EMCP method can not be made obsolete if it is not running.
>>>
>>
>>
>> It should be this way otherwise we'd have to hang onto things forever.
>
> An EMCP method should only be made obsolete if a RedefineClasses() or
> RetransformClasses() operation made it so. We should not be leveraging
> off the obsolete-ness attribute to solve a life-cycle problem.

Yes, this was my error in the change.  This is why I made things 
obsolete if they were not running.  I think I can't reuse this flag.  My 
latest changes add a new explicit flag (which we have space for in Method*).
>
> In the pre-PGR world, we could trust GC to make a completely unused
> EMCP method collectible and eventually our weak reference would go
> away. Just because an EMCP method is not on a stack does not mean
> that it is not used so we need a different way to determine whether
> it is OK to no longer track an EMCP method.

Our on_stack marking is supposed to look at all the places where GC used 
to look so I think we can use on_stack to track the lifecycle of EMCP 
methods.  If the EMCP method is somewhere, we will find it!

I'm running tests on the latest change, but am also waiting for 
confirmation from Roland because we were only cleaning out MethodData 
for EMCP methods and not for running obsolete methods and I think we 
need to do that for obsolete methods also, which my change does now.  I 
think it was a bug.

Thanks Dan for remembering all of this for me!

Coleen
>
>
>>
>>> BTW, I'm reviewing the webrev too, but probably it'd be better to 
>>> switch to updated webrev after it is ready.
>>
>> Yes, this is a good idea.  I figured out why I made emcp methods 
>> obsolete, and I'm fixing that as well as Dan's comments. Thanks!
>
> Cool! I'm looking forward to the next review.
>
> Dan
>
>
>>
>> Coleen
>>
>>>
>>> Thanks,
>>> Serguei
>>
>