Re: [Vm-dev] About primitive for cleaning compiled method cache

Hi Nicolas,

On 14 March 2013 00:13, Eliot Miranda <[hidden email]> wrote:
Hmm..

MethodDictionary>>at: key put: value
        "Set the value at key to be value."
        | index |
        index := self findElementOrNil: key.
        (self basicAt: index)
                ifNil:
                        [tally := tally + 1.
                        self basicAt: index put: key]
                ifNotNil:
                        [(array at: index) flushCache].
        array at: index put: value.
        self fullCheck.
        ^ value

CM>>flushCache uses primitive 116.
But look at the above implementation:
 it uses flushing only if you replacing existing method.

But not if you adding new method (like overriding in a subclass),
which you can simply expose with following:

Object subclass: #A
        instanceVariableNames: ''
        classVariableNames: ''
        poolDictionaries: ''
        category: 'TTT'

A>>foo
        ^ 'foo'

A subclass: #B
        instanceVariableNames: ''
        classVariableNames: ''
        poolDictionaries: ''
        category: 'TTT'

B>>zork
   ^ 'zork '
--
| x y |
x := B new foo.
B methodDict at: #foo put: (B>>#zork).
y := B new foo.
{  x. y }

gives:

 #('foo' 'foo')

while expected answer is
#('foo' 'zork') , of course.

Also gives same result, if i do:

A>>bar
        ^self foo

and invoke.
| x y |
x := B new bar.
B methodDict at: #foo put: (B>>#zork).
y := B new bar.
{  x. y }

 #('foo' 'foo')

Apparently, if we consider MethodDictionary>>at:put: as a last line of
defense (against bugs),
that line has a big breach, which needs to be fixed.




--
Best regards,
Igor Stasenko.

as a follow-up.. given the implementation of at:put:
i expected that following would work correctly:

| x y |
B methodDict removeKey: #foo ifAbsent: [ ].
x := B new bar.
B methodDict at: #foo put: (B>>#zork).
B methodDict at: #foo put: (B>>#zork).
y := B new bar.
{  x. y }

(a second at:put: shall trigger flushing the cache)..

yet it gives same answer:
 #('foo' 'foo')

Conclusion: primitive 116 is NOT enough.

While method's comment says otherwise:

flushCache
        "Tell the interpreter to remove all references to this method from
its method lookup cache, if it has one. This primitive must be called
whenever a method is redefined or removed.
        NOTE:  Only one of two selective flush methods (Symbol or
CompiledMethod) needs to be used."

        <primitive: 116>

--
Best regards,
Igor Stasenko.

2013/3/14 Igor Stasenko <[hidden email]>:
Yes the comment is for old VM and obsolete.
But see Behavior>>basicAddSelector:withMethod: and basicRemoveMethod,
they invoke primitive 119 unconditionnally.

Misunderstanding in this area is dangerous, so it's time to properly
document and clean if necessary, and kill false assumptions.

Nicolas

On 14 March 2013 09:29, Nicolas Cellier
<[hidden email]> wrote: yes, that makes invoking 116 unnecessary at all.
I am for putting this critical behavior into method dictionary..
then there is guarantee that no matter how you play with class(es) it
will flush things properly.

> Misunderstanding in this area is dangerous, so it's time to properly
> document and clean if necessary, and kill false assumptions.
>
> Nicolas
>



--
Best regards,
Igor Stasenko.