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

[Igor Stasenko]

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: []).

So, i thought its not a problem to reserve the 51 slot for weak
finalization, because it unused anyways.

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.

> Dave
>
>



-- 
Best regards,
Igor Stasenko AKA sig.