[Pharo-project] How to copy a CompiledMethod?

Gabriel Hernán Barbuto gbarbuto at gmail.com
Fri Nov 26 18:14:12 CET 2010


Eliot

Thanks for your response.

On Fri, Nov 26, 2010 at 5:49 PM, Eliot Miranda <eliot.miranda at gmail.com> wrote:
>
>
> On Thu, Nov 25, 2010 at 1:14 PM, Igor Stasenko <siguctua at gmail.com> wrote:
>>
>> On 25 November 2010 20:44, Gabriel Hernán Barbuto <gbarbuto at gmail.com>
>> wrote:
>> > Hi
>> >
>> > I am trying to make a complete duplicate of a CompiledMethod. I
>> > started with CompiledMethod>>#copyWithTrailerBytes: but I think that
>> > this way still leaves some things to copy. It duplicates all the
>> > literals, but I think that it doesn't duplicate a Pragma if for
>> > example, the method has one.
>> >
>> AFAIR, pragmas are stored as one of literals.
>> So, it actually should also make a copy of pragmas.
>
> Yes. pragmas are effectively referenced from literals.  If a method needs ti
> the penultimate literal (which otherwise is the method;s selector) holds an
> AdditionalMethodState which refers back to its method.  This needs to be
> copied if one is copying a method, since the backpointer needs to refer to
> the owning method, not the method form which the copy was made.
>>
>> > Is there a proper way to completely make deep copy of a
>> > CompiledMethod? I mean, without writing my own. If there is a way to
>> > do it, I don't want to duplicate it.
>> >
>> if you tell more, why #copy is not enough for you.
>
> If literals are read-only (and Array/ByteArray/String/Float literals are
> conceptually read-only but not actually) you don't need to make a deep copy.
>  You only need to copy the AdditionalMethodState, if present, and the class
> association, if you want to install the method somewhere else.

Yes that was exactly what I did. I handle both Association and
AdditionalMethodState in a special way and just send copy to all the
other literals. I was not sure what I could encounter in the literals
so I opted to send copy to them. Maybe they will just return
themselves or make an unnecessary duplicate.

I have also taken care of copying the Pragmas referenced from any
AdditionalMethodState. Igor mentioned that there could be Pragmas
directly on the literals but I am not sure about that. I will have to
get all the CompiledMethods and check if anyone has a Pragma among its
literals, but that is not enough, maybe my image doesn't have any.

I understand that all the literals are conceptually read only, and
that copying anything besides the Associations, AdditionalMethodStates
and Pragmas can waste memory and CPU cycles, but I am not interested
in speed nor memory consumption right now. But I will take a note, in
case some day I need to improve the copy.

After copying all the Associations, AdditionalMethodStates and Pragmas
that I've found I fix the references of both AdditionalMethodStates
and Pragmas to the new method in order to break all references to
objects in the current image that I don't want to show up in the new
image.

Thanks again.

Best
Gabriel

> best
> Eliot
>>
>> > Thanks in advance.
>> > Gabriel
>> >
>> >
>>
>>
>>
>> --
>> Best regards,
>> Igor Stasenko AKA sig.
>>
>
>




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