[9] RFR (S): 8060147: SIGSEGV in Metadata::mark_on_stack() while marking metadata in ciEnv

[Coleen Phillimore]

On 10/29/14, 11:05 AM, Vladimir Ivanov wrote:
> Bertrand,
>
> Thanks for the review.
>
> There's another mechanism to support class redefinition - 
> MetadataOnStackMark. It iterates over all threads and sets on_stack 
> bit on every Metadata* it encounters. It keeps metadata from clearing.
>
> Eventually, it calls ciObjectFactory::metadata_do() for every compiler 
> thread which marks all Metadata* in associated 
> ciObjectFactory::_ci_metadata.

Yes, this is true.

Thank you for renaming get_new_object into get_new_metadata and fixing 
some of the comments.

There comment above create_new_metadata needs updating:

  346 // ------------------------------------------------------------------
  347 // ciObjectFactory::create_new_object
  348 //

Lines 359-367 should be a method in metadata.hpp because there are now 
several instances of it.   Can you make this change or file an RFE for this?

Thanks,
Coleen

>
> Best regards,
> Vladimir Ivanov
>
> On 10/29/14, 7:24 PM, Bertrand Delsart wrote:
>> Hi Vladimir,
>>
>> This seems OK with respect to class unloading but what about class
>> redefinition ?
>>
>> In particular, this may not be sufficient for Method* or MethodData*.
>> Still catching up on runtime issues but I think a redefined method has a
>> smaller lifetime than its holder class. Hence, it seems that keeping the
>> holder klass alive may not be sufficient to ensure a Method* survives as
>> long as you need it for the ciMetadata.
>>
>> Regards,
>>
>> Bertrand.
>>
>> On 29/10/14 14:57, Vladimir Ivanov wrote:
>>> http://cr.openjdk.java.net/~vlivanov/8060147/webrev.00
>>> https://bugs.openjdk.java.net/browse/JDK-8060147
>>>
>>> ciObjectFactory doesn't keep cached Metadata* alive. ciMetadata is
>>> different from ciObject - it doesn't store JNI handle, but a raw
>>> Metadata* pointer.
>>>
>>> In order to avoid Metadata* vanishing during compilation, I cache
>>> ciObject for it's holder, which should keep corresponding Metadata*
>>> alive. Cached objects have the same lifetime as the owning
>>> ciObjectFactory (no cache pruning), so Metadata* will be available as
>>> long as ciObjectFactory instance is used.
>>>
>>> Also, cleaned relevant comments and strengthened some asserts (since
>>> NULL keys are not allowed).
>>>
>>> Testing: jprt, stress mode - full Nashorn/Octane with aggressive VM
>>> anonymous class unloading (LambdaForm/MethodHandle caching completely
>>> turned off).
>>>
>>> Thanks!
>>>
>>> Best regards,
>>> Vladimir Ivanov
>>
>>