[Pharo-project] Ideas for CompiledMethod proxies?

Mariano Martinez Peck marianopeck at gmail.com
Tue Nov 30 23:55:56 CET 2010


On Tue, Nov 30, 2010 at 11:45 PM, Eliot Miranda <eliot.miranda at gmail.com>wrote:

>
>
> On Tue, Nov 30, 2010 at 2:33 PM, Mariano Martinez Peck <
> marianopeck at gmail.com> wrote:
>
>> Thanks to both for answering me.
>> Now, I have very very newbie question.
>> In my case, JUST BECAUSE i am testing, I directly access the
>> CompiledMethod using MethodDictionary >> #at:ifAbsent:
>> thus, I can intercept and load back the original proxy.
>>
>> Now, if I understood well, when you send a simple message to an object,
>> the method lookup is done at VM side, and there is no call to
>> MethodDictionary >> #at:ifAbsent:
>>
>> So, what I am saying is that someone (the system) can send messages to a
>> SmallInteger that acts as a compiled methods, without accessing it by
>> MethodDictionary >> #at:ifAbsent:.
>> If that message is understood by the SmallInetger, then it will probably
>> answer something different than the original method.
>>
>
> You're forgetting that the VM executes the methods it finds in a method
> dictionary, except if the VM finds other than a CompiledMethod in a method
> dictionary, in which case it sends run:with:in: to it.  So the VM won't send
> anything to the SmallInteger method proxy other than run:with:in:.  If it
> didn't send run:with:in: it would crash trying to execute the SmallInteger.
>
>
I think we are confusing exatly like we were confusing yesterday with my
supervisors.

Eliot, one thing is to do this:

MyClass methodDict at: #foo put: 5.
MyClass new foo.

Here I am SURE the VM will send #run:with:in to SmallInteger.

Now, my question is when I send a MESSAGE to the CompiledMethod, and NOT to
the object which class has installed the compiled method.

Suppose I do:  (MyClass methodDict at: #foo) size.   and that I don't change
the implementation of MethodDictionary >> #at:ifAbsent:

In this case, the VM will just try to send the message size to that whatever
is there. Both, SmallInteger and CompiledMethod understand #size, but both
answer different things...
I cannot intercept this, and I cannot load back the original object.

This is why with Levento we thought about modifying MethodDictionary >>
#at:ifAbsent:  to something like this:

at: key ifAbsent: aBlock

    | index value |
    index := self findElementOrNil: key.
    (self basicAt: index) == nil ifTrue: [ ^ aBlock value ].
    value := array at: index.
    (value mareaIsProxy) ifTrue: [value mareaUninstall].
    ^ array at: index


But then, my question is if the system may access by another way than that
one. Ok, I should also modify some other methods in MethodDictionary like
#valuesDo:  etc,,,
but if I do that, is that enough?   or the system can still send messages
without passing there?

Thanks a lot!

mariano





> best
> Eliot
>
>>
>> Now, maybe what I am thinking cannot happen.
>>
>> Thanks once again
>>
>> Mariano
>>
>>
>>
>> On Tue, Nov 30, 2010 at 10:23 PM, Levente Uzonyi <leves at elte.hu> wrote:
>>
>>> On Tue, 30 Nov 2010, Igor Stasenko wrote:
>>>
>>>  .. and then you need to change #do: , #associationsDo: etc etc..
>>>>
>>>
>>> Or he can subclass MethodDictionary and override those methods.
>>>
>>>
>>> Levente
>>>
>>>
>>
>
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