[Vm-dev] Re: [Pharo-project] is it possible to know the memory occupation (bytes) of an object?

[Henrik Johansen]

On Sep 28, 2010, at 9:36 27AM, Mariano Martinez Peck wrote:

> 
> 
> On Tue, Sep 28, 2010 at 6:46 AM, Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com> wrote:
> 
> 2010/9/27 Eliot Miranda <eliot.miranda at gmail.com>:
> >
> >
> >
> > On Mon, Sep 27, 2010 at 12:20 PM, Mariano Martinez Peck <marianopeck at gmail.com> wrote:
> >>
> >>
> >>
> >>
> >> On Wed, Sep 22, 2010 at 12:34 PM, Mariano Martinez Peck <marianopeck at gmail.com> wrote:
> >>>
> >>>
> >>> On Wed, Sep 22, 2010 at 12:12 PM, Henrik Johansen <henrik.s.johansen at veloxit.no> wrote:
> >>>>
> >>>> On Sep 22, 2010, at 9:59 40AM, Adrian Lienhard wrote:
> >>>>
> >>>> > Some notes:
> >>>> >
> >>>> > - What should be answered for small ints? 1 sizeInMemory -->8. That's wrong. Shouldn't this answer 0?
> >>>>
> >>>> Philosophical question really, imo both 4 (Again, in 32bit images at least) and 0 would be "correct" answers in their own ways. 8 is definitely wrong though :)
> >>>> The method comment should probably highlight which definition is used.
> >>>>
> >>
> >>
> >> So....what should we consider for SmallInteger ?   4 bytes or 0 bytes?
> >
> > 0 bytes, obviously.  The only space occupied by a SmallInteger is the space of the slot containing it.  There is no SmallInteger object beyond the slot.
> >
> 
> Or from another POV, it's 4, the size of the slot. But we don't count
> the size of the slots, they are already counted in the containing
> object, that's why it should answer 0.
> 
> 
> Thanks for the answers. I finally let this:
> 
> sizeInMemory
>     "Answer the number of bytes consumed by this instance including object header."
>     | isCompact headerBytes contentBytes |
> 
>     "SmallInteger occupy 0 bytes since the only space occupied by a SmallInteger is the space of the slot containing it.  There is no SmallInteger object beyond the slot. From another POV, it could be 4, the size of the slot. But we don't count the size of the slots, they are already counted in the containing object, that's why it should answer 0."
>     (self isMemberOf: SmallInteger) ifTrue: [^0]. 
> 
>      contentBytes := self class instSize * Smalltalk wordSize. "inst vars"
> 
>      self class isVariable ifTrue:[ |bytesPerElement|
>             bytesPerElement := self class isBytes ifTrue: [1] ifFalse: [4].
>             contentBytes := contentBytes + (self basicSize * bytesPerElement)].
> 
>      isCompact := self class indexIfCompact > 0.
>       headerBytes :=
>                     contentBytes > 255
>                         ifTrue: [ 3 * Smalltalk wordSize ] 
>                         ifFalse: [isCompact ifTrue: [Smalltalk wordSize] ifFalse: [2 * Smalltalk wordSize]].
>             ^ headerBytes + contentBytes
> 
> 
> Now I wonder...maybe instead of doing this it is easier to have a primitive that just calls #internalByteSize: ?
> The problem of course is that it needs changes in the vm...
> 
> cheers
> 
> Mariano
>  
isMemberOf: is so quaint...

Why not 
SmallInteger>>sizeInMemory
	    "SmallInteger occupy 0 bytes since the only space occupied by a SmallInteger is the space of the slot containing it.  
		There is no SmallInteger object beyond the slot. 
		From another POV, it could be 4, the size of the slot. But we don't count the size of the slots, they are already counted in the containing object, that's why it should answer 0."
	^0

and remove that part from the Object implementation.

Cheers,
Henry
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