[Vm-dev] Special objects array - sometimes everybody cannot be special

[Igor Stasenko]

On 25 May 2010 15:30, David T. Lewis <lewis at mail.msen.com> wrote:
>
> On Tue, May 25, 2010 at 08:19:43AM +0300, Igor Stasenko wrote:
>>
>> On 25 May 2010 06:56, David T. Lewis <lewis at mail.msen.com> wrote:
>> >
>> > We have some contention for slots in the special objects array. The Alien
>> > package lays claim to slots 50 - 54, and Igor's improved finalization
>> > would like to use slot 50. The Alien claim predates the Finalizer claim
>> > (albeit only through an *Extentions in Alien-VMMaker-Support), and there
>> > may already be people running VMs that rely on these special object
>> > assignments. On the other hand, finalization is part of the core system,
>> > so it would have been nice to put ClassWeakFinalizer at slot 50, and the
>> > optional Alien assignments at 51 - 55.
>> >
>> > Would anyone object to the following allocation of slots in the special
>> > objects array? This would leave Alien mostly unaffected, but would require
>> > Igor's finalization improvements to put WeakFinalizer at position 55 in
>> > the special objects array, and it would require that the Alien override
>> > be pulled into the VMMaker package such that all VMs would have the Alien
>> > assignments in the special objects array (albeit unused in many cases).
>> > And recreateSpecialObjectsArray would need updates to match of course.
>> >
>> > ?? ?? ?? ??SelectorAttemptToAssign := 50.
>> > ?? ?? ?? ??"PrimErrTableIndex := 51. in Interpreter class>>initializePrimitiveErrorCodes"
>> > ?? ?? ?? ??ClassAlien := 52.
>> > ?? ?? ?? ??InvokeCallbackSelector := 53.
>> > ?? ?? ?? ??ClassUnsafeAlien := 54.
>> > ?? ?? ?? ??ClassWeakFinalizer := 55
>> >
>> > I seem to recall some discussion of a more flexible special objects
>> > registry, although I can't find it right now. Pointers welcome.
>> >
>>
>> Ouch.. David, it seems like i used the different version of
>> #recreateSpecialObjectsArray
>> than yours.
>>
>> The tail of spl objects in Alien-Core package, found at  SqS/Alien
>> looks like following:
>>
>>       newArray at: 50 put: #run:with:in:.
>>       newArray at: 51 put: nil.
>>       newArray at: 52 put: nil.
>>       newArray at: 53 put: (self at: #Alien ifAbsent: []).
>>       newArray at: 54 put: #invokeCallback:stack:registers:jmpbuf:.
>>       newArray at: 55 put: (self at: #UnsafeAlien ifAbsent: []).
>
> Note that ObjectMemory class>>initializeSpecialObjectIndices uses zero-based
> indexing, versus one-based indexing in SmalltalkImage>>recreateSpecialObjectsArray,
> so I think the difference is not a problem.
>
>> So, i thought its not a problem to reserve the 51 slot for weak
>> finalization, because it unused anyways.
>
> Well, the slot for PrimErrTableIndex does appear to be unused at the moment,
> but I suspect that either Eliot or John reserved it for a reason. If it is
> actually unused, then this would be a good place to put ClassWeakFinalizer
> (i.e. ClassWeakFinalizer would go in 51 initializeSpecialObjectIndices, which
> would be 52 in the special objects array, right before ClassAlien).
>
No, in my changesets its 51 in image and 50 in VMMaker.
But it don't matters much. So, if you say 55, let it be 55.

>> Also, maybe we could fill an unused/obsolete slot instead of allocating new one?
>>  There are some:
>>
>>       newArray at: 23 put: nil.
>>       newArray at: 41 put: nil.
>>
>
> I think that these slots are probably still used in older images. But it
> would be good idea if we can safely recycle them.
>
> Dave
>
>



-- 
Best regards,
Igor Stasenko AKA sig.