[Pharo-project] Problem with CompiledMethodTrailer

Henrik Sperre Johansen henrik.s.johansen at veloxit.no
Tue May 10 13:33:28 CEST 2011


On 10.05.2011 12:44, Igor Stasenko wrote:
> On 10 May 2011 11:27, Mariano Martinez Peck<marianopeck at gmail.com>  wrote:
>>
>> On Tue, May 10, 2011 at 10:59 AM, Igor Stasenko<siguctua at gmail.com>  wrote:
>>> On 10 May 2011 09:48, Mariano Martinez Peck<marianopeck at gmail.com>  wrote:
>>>>
>>>> On Tue, May 10, 2011 at 9:41 AM, Marcus Denker<marcus.denker at inria.fr>
>>>> wrote:
>>>>> On May 10, 2011, at 9:32 AM, Mariano Martinez Peck wrote:
>>>>>
>>>>>> what is even worst, is that even after removing those correct CM, and
>>>>>> doing a GC etc...they still don't disappear.
>>>>>>
>>>>> There is
>>>>>
>>>>>         ScriptLoader new cleanUpMethods
>>>>>
>>>>> This is called from #cleanUpForRelease and normally should make sure
>>>>> there
>>>>> are no old methods.
>>>>>
>>>>
>>>> hehehehe if I do: ScriptLoader new cleanUpForRelease, then inspect
>>>> ((CompiledMethod allInstances select:  [:each | each trailer kind =
>>>> #VarLengthSourcePointer] ) )
>>>>
>>>> they are not GC'ed and if then I click on the first element in the
>>>> inspector.... VM CRASH!!!  with both, InterpreterVM and CogVM.
>>>>
>>>> :(
>>>>
>>> okay. it seems i found the offender. Its a CompiledMethod class>>cleanUp.
>>> It changing a source pointer of all non-installed methods to 0.
>> Good catch!!!  :)   Anyway, why CompiledMethod class>>cleanUp would like to
>> destroy source pointers???
>> If I understood correctly (please correct me), all compiled methods will
>> loose the pointer to sources and hence they will be decompiled after when
>> they are ask their source!
> Yes, if you wipe the sourcePointer, there is no way how you can get a
> source code of method.
I believe the "not getting the source code" was on purpose.
It's done f.ex. as part of condenseChanges, as the source pointers would 
have been invalid anyways.
The intent I believe is that you should get decompiled source if you 
inspect old(but still referenced) CompiledMethods, instead of a bogus 
display of some random part of the new changes file, and remove error 
handling in source lookup where pointer could potentially be beyond end 
of file.

This of course worked much faster before trailers, when 
setSourcePointer: actually modified the instance inline, rather than 
become'ing a copy, nowadays I agree with Igor that it'd probably be more 
conceptually clean to the empty MethodTrailer in destroySourcePointer :)

Just remember to make sure such instances decompile as expected to 
uphold why the zapping was done in the first place.
If we're lucky,  it won't crash the VM either ;)

Cheers,
Henry



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