[Vm-dev] Re: [Pharo-project] Bug in WAMemoryItem>>sizeOfObject

[Mariano Martinez Peck]

And there is also #sizeInMemory

sizeInMemory
    "Answer the number of bytes consumed by this instance including object
header."
    | contentBytes |

    contentBytes := Smalltalk wordSize. "base header"
    contentBytes := contentBytes + (self class instSize * Smalltalk
wordSize). "instance vars"

    self class isVariable ifTrue:[ | bytesPerElement | "indexed elements"
        bytesPerElement := self class isBytes ifTrue: [1] ifFalse: [4].
        contentBytes := contentBytes + (self basicSize * bytesPerElement)
    ].

    contentBytes > 255 ifTrue:    [ contentBytes := contentBytes +  (2 *
Smalltalk wordSize) ]
                        ifFalse:    [ self class isCompact
                                    ifFalse: [ contentBytes := contentBytes
+ Smalltalk wordSize]
                                ].
    ^contentBytes



which is also wrong for the cases of String. For example, 'aa' sizeInMemory
answers 6 but should be 8 because of alligment.
If someone fixes this, I think #sizeInMemory would be correct.

Cheers

On Thu, Mar 15, 2012 at 6:53 PM, Eliot Miranda <eliot.miranda at gmail.com>wrote:

>
> Hi Niko,
>
>     the header size calculation is also wrong.  If the byte size if the
> object body is > 255 bytes there needs to be an additional header size
> word.  So something like
>
>        byteSizeOfBody := anObject class isBytes
>                                        ifTrue: [....]
>                                        ifFalse: [.....].
>        headerSize := byteSizeOfBody > 255
>                                ifTrue: [12]
>                                ifFalse:
>                                      [anObject class indexIfCompact > 0
>                                           ifTrue: [4]
>                                           ifFalse: [8]].
>
> On Wed, Mar 14, 2012 at 1:05 PM, <niko.schwarz at googlemail.com> wrote:
>
>> Hi guys,
>>
>> I haven't checked if this bug exists already, so please ignore this if
>> it's been reported before.
>>
>> Bug in WAMemoryItem:
>>
>> sizeOfObject: anObject
>>        | headerSize instanceSize variableSize |
>>        headerSize := anObject class indexIfCompact > 0
>>                ifTrue: [ 4 ]
>>                ifFalse: [ 8 ].
>>        instanceSize := anObject class instSize.
>>        variableSize := anObject class isBytes
>>                ifTrue: [ anObject basicSize ]
>>                ifFalse: [
>>                        anObject class isWords
>>                                ifTrue: [ Smalltalk wordSize * anObject
>> basicSize ]
>>                                ifFalse: [ Smalltalk wordSize * anObject
>> basicSize // 2 ] ].
>>        ^ headerSize + instanceSize + variableSize
>>
>>
>> In this snippet, the units that are added together in the last line are
>> of different units.
>>
>> instanceSize is in unit "number of machine words", whereas variableSize
>> and headerSize are in unit "bytes".
>>
>>
>> The method is fixed here:
>>
>> sizeOfObject: anObject
>>        | headerSize instanceSize variableSize |
>>        headerSize := anObject class indexIfCompact > 0
>>                ifTrue: [ 4 ]
>>                ifFalse: [ 8 ].
>>        instanceSize := anObject class instSize * Smalltalk wordSize.
>>        variableSize := anObject class isBytes
>>                ifTrue: [ anObject basicSize ]
>>                ifFalse: [
>>                        anObject class isWords
>>                                ifTrue: [ Smalltalk wordSize * anObject
>> basicSize ]
>>                                ifFalse: [ Smalltalk wordSize * anObject
>> basicSize // 2 ] ].
>>        ^ headerSize + instanceSize + variableSize
>>
>>
>>
>> Example:
>>
>>  |m|
>> dict := Dictionary new.
>> m := WAMemory new. dict traverseWithMemory: m seen: IdentitySet new.
>> m totalSize
>>
>> This will incorrectly spit out 10, but should return 16, on a 32 bit VM.
>>
>> Niko
>>
>> --
>> http://scg.unibe.ch/staff/Schwarz
>> twitter.com/nes1983
>> Tel: +41786126354
>>
>>
>>
>
>
> --
> best,
> Eliot
>
>
>


-- 
Mariano
http://marianopeck.wordpress.com
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