RFR 8145964: NoClassDefFound error in transforming lambdas

[Daniel D. Daugherty]

Hi David,

Need to chime in on a couple of parts from earlier in the thread.


On 8/14/16 10:05 PM, David Holmes wrote:
> Hi Dan,
>
> On 15/08/2016 12:20 PM, Daniel D. Daugherty wrote:

<snip>

>
>> There are various places that refer to can_redefine_any_class. Those 
>> places
>> also need updating. Here's the one from RedefineClasses:
>>
>>> can_redefine_any_class    Can modify (retransform or redefine) any
>> non-primitive
>>>                           non-array class. See IsModifiableClass.
>>
>> Should probably be changed to something like:
>>
>> can_redefine_any_class    Can modify (retransform or redefine) any class
>> except for
>>                           a few specific classes. See IsModifiableClass
>> for the classes
>>                           that cannot be modified.
>
> <sigh> This is so frustrating. Why even bother with the notion of 
> IsModifiableClass (which suggests any class might be non-modifiable 
> under some circumstances) when it is then completely undermined by the 
> can_redefine_any_class capability? If the intent was that only 
> primitives and arrays are ever non-modifiable then that should have 
> simply been listed in the spec for RedefineClasses and 
> restransformClasses, instead of introducing IsModifiableClass. 
> Otherwise can_redefine_any_class should simply refer to 
> IsModifiableClass.

Acquiring a capability is how an agent tells the VM what it plans to do.
When an agent acquires can_redefine_classes or can_retransform_classes,
it is telling the VM that it plans to use redefine classes or class
tranformation. When an agent acquires can_redefine_any_class or
can_retransform_any_class, it is telling the VM that it plans to use
redefine classes or class transformation on as many classes as possible
so it would be a good idea to disable some optimizations like sharing.

A properly written agent will check possible target classes with
IsModifiableClass() before attempting redefine classes regardless of
whether the agent has acquired just can_redefine_classes or both
can_redefine_classes and can_redefine_any_class. This is similarly
true for class transformation and the can_retransform_classes and
can_retransform_any_class capabilities.

We should probably update the wording for all four capabilities to
refer to IsModifiableClass() so that we can avoid having the same
wording in multiple places.


<snip>

> The only thing that needs fixing in my opinion is the definition of 
> can_redefine_any_class to not refer to primitives or arrays but simply 
> to any class for which IsModifiableClass returns true!

Yup. That's where we should go, but we should do it for all four
capabilities.


>
> can_redefine_any_class is really puzzling if you consider 
> can_redefine_classes. It is far from clear to me what set of classes 
> can_redefine_any_class gives access to that can_redefine_classes does 
> not ??? What purpose do two capabilities serve here?

can_redefine_classes and can_retransform_classes are needed if you
are going to redefine classes or transform classes at all. The "any"
capabilities are provided as a way to indicate that your agent
intends to redefine or transform as many classes as possible
including those that might normally have other optimizations applied
to them, e.g., sharing.

Dan