RFR 8145964: NoClassDefFound error in transforming lambdas

Coleen Phillimore coleen.phillimore at oracle.com
Mon Aug 15 23:37:53 UTC 2016 


On 8/15/16 2:17 PM, Tom Rodriguez wrote:
>>>
>>> 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.
>
> Sorry, I was away on vacation so I couldn’t respond to this earlier. 
>  In principle I agree with David that from an API perspective 
> anonymous classes should just be treated as unmodifiable.  I don’t 
> completely understand the compatibility issue this presents though. 
>  The only way an agent should be encountering them is if it gets all 
> loaded classes and then passes that result back through redefine 
> classes.  Presumably they must be filtering out the array classes from 
> that list already.  If they are using IsModifiable for this then it 
> would all work out great but they could just be filtering on isArray, 
> which seems most likely to me.

That's good.  I'm glad that there isn't a compatibility problem.  I 
guess there wouldn't be since the reported applications got 
NoClassDefFoundError, now they'll get an UnmodifiableClassException but 
can call isModifiableClass first anyway.

>
> Given that the anonymous classes become unusable after redefinition 
> I’d have to assume that agents which encountered this problem have 
> worked around it themselves.  The netbeans profiler worked about this 
> by filtering out class names with a “/“ in them. 
> http://hg.netbeans.org/main-silver/rev/ed472a217546 
> https://netbeans.org/bugzilla/show_bug.cgi?id=245840 This is fairly 
> similar to silently ignoring them which is part of why I suggested 
> that fix in my report.
>
> So I think the right fix for 9 is to treat this an an API 
> clarification and make them unmodifiable.  Any agent which isn’t 
> already handling this themselves is broken but doesn’t know it yet.  I 
> assume there’s no intent to fix this in 8?
>

Great.  I can probably backport it to 8, when we get the details sorted 
out wrt the spec.

thanks,
Coleen

> tom
>
>>
>>> Similar wording change in the jvmtiCapabilities table that lists
>>> can_redefine_any_class. Of course, IsModifiableClass itself will
>>> have to be updated to spell out the classes that can't be modified.
>>>
>>> Looks like the spec wording for can_retransform_any_class is pretty
>>> much wrong w.r.t. IsModifiableClass() stuff and will all need work.
>>> Also looks like can_retransform_any_class wording is completely
>>> missing from IsModifiableClass().
>>>
>>> Sorry this is turning into a can of worms...
>>
>> We may have to switch to option 2 and just silently ignore everything 
>> related to VMACs.
>>
>> That said I don't think that we have to spell out every potential 
>> case where a class may be unmodifiable. It should be sufficient (as 
>> currently stated) that you can't redefine or retransform an 
>> unmodifiable class. 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!
>>
>> 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?
>>
>> David
>> -----
>>
>>> Dan
>>>
>>>
>>>>
>>>> thanks,
>>>> Coleen
>>>>>
>>>>> Thanks,
>>>>> David
>>>>>
>>>>>> Thanks,
>>>>>> Coleen
>>>>>>
>>>>>> On 8/11/16 11:44 PM, David Holmes wrote:
>>>>>>> On 12/08/2016 12:23 AM, Coleen Phillimore wrote:
>>>>>>>> On 8/11/16 8:20 AM, David Holmes wrote:
>>>>>>>>> On 11/08/2016 10:09 PM, Coleen Phillimore wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On 8/10/16 8:37 PM, David Holmes wrote:
>>>>>>>>>>> Hi Coleen,
>>>>>>>>>>>
>>>>>>>>>>> On 11/08/2016 12:45 AM, Coleen Phillimore wrote:
>>>>>>>>>>>>
>>>>>>>>>>>> New webrev:
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> http://cr.openjdk.java.net/~coleenp/8145964.02/webrev/index.html 
>>>>>>>>>>>> <http://cr.openjdk.java.net/%7Ecoleenp/8145964.02/webrev/index.html>
>>>>>>>>>>>
>>>>>>>>>>> First I'm very surprised that the existing logic in
>>>>>>>>>>> JvmtiEnv::RetransformClasses doesn't utilize
>>>>>>>>>>> VM_RedefineClasses::is_modifiable_class to determine when to
>>>>>>>>>>> return
>>>>>>>>>>> JVMTI_ERROR_UNMODIFIABLE_CLASS. It would seem easy for the two
>>>>>>>>>>> bits of
>>>>>>>>>>> code to get out of sync!
>>>>>>>>>>>
>>>>>>>>>>> Second, why do you silently ignore an attempt to redefine an
>>>>>>>>>>> anonymous
>>>>>>>>>>> class instead of returning JVMTI_ERROR_UNMODIFIABLE_CLASS? The
>>>>>>>>>>> restriction on transforming anonymous classes seems no different
>>>>>>>>>>> to me
>>>>>>>>>>> to the restriction on transforming primitive or array classes.
>>>>>>>>>>
>>>>>>>>>> I believe that there are existing applications, as in the 
>>>>>>>>>> test, get
>>>>>>>>>> all
>>>>>>>>>> the loaded classes and try to transform them.  These will get
>>>>>>>>>> the VM
>>>>>>>>>> anonymous class, so we didn't want to give them an error. Or set
>>>>>>>>>> CLFH
>>>>>>>>>> and vm anonymous classes fall into the load hook. There's
>>>>>>>>>> another bug
>>>>>>>>>> that Rachel has that ignores them for CFLH (rather than 
>>>>>>>>>> crashing).
>>>>>>>>>>
>>>>>>>>>> From the Java standpoint, the existence of vm anonymous classes
>>>>>>>>>> are a
>>>>>>>>>> implementation detail and not real classes, and it's better 
>>>>>>>>>> to hide
>>>>>>>>>> these as much as possible.
>>>>>>>>>
>>>>>>>>> I think this is a mistake. While anonymous classes may have
>>>>>>>>> started as
>>>>>>>>> some obscure VM implementation detail related to JSR-292 and
>>>>>>>>> InvokeDynamic they are now entities that are prevalent in a 
>>>>>>>>> running
>>>>>>>>> Java application due to the extensive use of Methodhandles and 
>>>>>>>>> their
>>>>>>>>> use by lambda expressions. Unless we can hide such classes
>>>>>>>>> completely
>>>>>>>>> (we can't!) we need to define their semantics when treated like
>>>>>>>>> other
>>>>>>>>> "normal" Java classes. This should have been addressed for JVM TI
>>>>>>>>> when
>>>>>>>>> anonymous classes came into existence but it wasn't. But we 
>>>>>>>>> have to
>>>>>>>>> deal with it, so simply define them as non-modifiable classes just
>>>>>>>>> like array classes and primitives. If code gets an error that is
>>>>>>>>> good
>>>>>>>>> it _needs_ to get an error because it needs to realize that it is
>>>>>>>>> dealing with anonymous classes not "real" ones!
>>>>>>>>>
>>>>>>>>
>>>>>>>> I disagree, and please read the bug where the consensus is that we
>>>>>>>> should ignore these for retransformation.  Redefinition is a
>>>>>>>> different
>>>>>>>> matter because you have to give the class with new bytecodes, which
>>>>>>>> would be very bad, and that's why I chose to give an error message.
>>>>>>>
>>>>>>> I don't read such a consensus in the bug report.
>>>>>>>
>>>>>>>> This is John Rose's answer to a similar question:
>>>>>>>>
>>>>>>>> http://mail.openjdk.java.net/pipermail/core-libs-dev/2016-January/038353.html
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>> Yes I added that link to the bug report initially. It reinforces 
>>>>>>> that
>>>>>>> retransform/redefinition of VMAC is not intended to work  so 
>>>>>>> don't do
>>>>>>> that: "Please don't lead your users to rely on them."
>>>>>>>
>>>>>>> I read more in John's response that the code doing the 
>>>>>>> transformations
>>>>>>> should be skipping the VMAC's, than that the VM code should 
>>>>>>> ignore the
>>>>>>> VMAC's if passed in.
>>>>>>>
>>>>>>> The current situation is inconsistent and that is what I object to,
>>>>>>> most strenuously. When I suggested this be handled through
>>>>>>> VM_RedefineClasses::is_modifiable_class I was expecting the VMAC 
>>>>>>> to be
>>>>>>> treated as an unmodifiable class in all cases/sense. It is not
>>>>>>> acceptable to me to have IsModifiableClass return false yet
>>>>>>> retransform does not report JVMTI_ERROR_UNMODIFIABLE_CLASS. There
>>>>>>> should be tests that check that the two are consistent!
>>>>>>>
>>>>>>> Please, either silently ignore it everywhere, or else deal with it
>>>>>>> consistently as unmodifiable.
>>>>>>>
>>>>>>>> I am not willing to break existing applications.
>>>>>>>
>>>>>>> Any existing application that retransforms an anonymous class is
>>>>>>> already in unchartered waters. To quote John "Even if you were 
>>>>>>> able to
>>>>>>> 'transform' one of these classfiles, it wouldn't necessary do 
>>>>>>> what you
>>>>>>> think it should do". So if it is lucky any existing code that 
>>>>>>> attempts
>>>>>>> to transform an anonymous class simply does no harm - but more 
>>>>>>> likely
>>>>>>> it gets an error (as per this bug report), or worse it "does 
>>>>>>> something
>>>>>>> you didn't think it would do"! If such code is now run against JDK 9
>>>>>>> then I think they would be grateful to be told that they are running
>>>>>>> broken code, and exactly where it is broken.
>>>>>>>
>>>>>>> Cheers,
>>>>>>> David
>>>>>>>
>>>>>>>> Coleen
>>>>>>>>
>>>>>>>>> Cheers,
>>>>>>>>> David
>>>>>>>>>
>>>>>>>>>> Coleen
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Thanks,
>>>>>>>>>>> David
>>>>>>>>>>>
>>>>>>>>>>>> Reran jvmti tests.
>>>>>>>>>>>>
>>>>>>>>>>>> Thanks,
>>>>>>>>>>>> Coleen
>>>>>>>>>>>>
>>>>>>>>>>>> On 8/10/16 9:32 AM, Coleen Phillimore wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> On 8/9/16 7:40 PM, David Holmes wrote:
>>>>>>>>>>>>>> Hi Coleen,
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On 10/08/2016 4:52 AM, Coleen Phillimore wrote:
>>>>>>>>>>>>>>> Summary: Skip VM anonymous classes in retransformation and
>>>>>>>>>>>>>>> give an
>>>>>>>>>>>>>>> error
>>>>>>>>>>>>>>> for redefinition.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Contributed by Tom Rodriguez.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Tested with redefinition colocated tests (tonga) and
>>>>>>>>>>>>>>> java/lang/instrument tests, and added test case.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> open webrev at
>>>>>>>>>>>>>>> http://cr.openjdk.java.net/~coleenp/8145964.01/webrev 
>>>>>>>>>>>>>>> <http://cr.openjdk.java.net/%7Ecoleenp/8145964.01/webrev>
>>>>>>>>>>>>>>> bug link https://bugs.openjdk.java.net/browse/JDK-8145964
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Shouldn't anonymous classes be added to the set of
>>>>>>>>>>>>>> non-modifiable
>>>>>>>>>>>>>> classes - so IsModifiableClass returns false and we just add
>>>>>>>>>>>>>> this
>>>>>>>>>>>>>> case to VM_RedefineClasses::is_modifiable_class.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Yes, that might be a better way to do it.
>>>>>>>>>>>>> thanks,
>>>>>>>>>>>>> Coleen
>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> ??
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>> David
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>>> Coleen
>

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