RFR (S): 8060147: SIGSEGV in Metadata::mark_on_stack() while marking metadata in ciEnv
bertrand.delsart at oracle.com
Wed Oct 29 17:55:05 UTC 2014
I had forgotten that the GC no longer needs to walk the metadata by
default and now understand why you need to instead explicitly keep the
Java holder alive.
Bertrand, not a Reviewer.
On 29/10/14 16:05, Vladimir Ivanov wrote:
> 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
> 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.
>> On 29/10/14 14:57, Vladimir Ivanov wrote:
>>> 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).
>>> Best regards,
>>> Vladimir Ivanov
Bertrand Delsart, Grenoble Engineering Center
Oracle, 180 av. de l'Europe, ZIRST de Montbonnot
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