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Why 2017 sizeInMemory = 0?

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Denis Kudriashov

Why 2017 sizeInMemory = 0?

Hi.

Question from discord, why:

2017 sizeInMemory = 0

Looks like a bug, but maybe there is some reason for this.

Marcus Denker-4

Re: Why 2017 sizeInMemory = 0?

On 26 Oct 2017, at 10:05, Denis Kudriashov <[hidden email]> wrote:

Hi.

Question from discord, why:

2017 sizeInMemory = 0

?

Looks like a bug, but maybe there is some reason for this.

#sizeInMemory only takes into account object header size and the size of the object

itself.

A small-integer is encoded in the pointer, so it has no size in itself, only the object

pointing to it needs space for the pointer, just like for normal object.

Marcus

tesonep@gmail.com

Re: Why 2017 sizeInMemory = 0?

In reply to this post by Denis Kudriashov

Because it is an immediate value.

On 26 Oct 2017 10:06, "Denis Kudriashov" <[hidden email]> wrote:

Hi.

Question from discord, why:

2017 sizeInMemory = 0

?

Looks like a bug, but maybe there is some reason for this.

Eliot Miranda-2

Re: Why 2017 sizeInMemory = 0?

In reply to this post by Marcus Denker-4

Hi Marcus,

On Thu, Oct 26, 2017 at 1:09 AM, Marcus Denker <[hidden email]> wrote:

On 26 Oct 2017, at 10:05, Denis Kudriashov <[hidden email]> wrote:

Hi.

Question from discord, why:

2017 sizeInMemory = 0

?

Looks like a bug, but maybe there is some reason for this.

#sizeInMemory only takes into account object header size and the size of the object
itself.

sizeInMemory is also ignorant of details such as the padding of objects to 64-bits in both 32-bit and 64-bit Spur, the overflow header when there are more than 254 slots, etc. siseInMemory should really be implemented like this:

Object>>sizeInMemory

^self class isVariable

ifTrue: [self class byteSizeOfInstanceOfSize: self basicSize]

ifFalse: [self class byteSizeOfInstance]

where the subsidiary definitions are

Behavior>>byteSizeOfInstance

"Answer the total memory size of an instance of the receiver."

<primitive: 181 error: ec>

self isVariable ifTrue:

[^self byteSizeOfInstanceOfSize: 0].

self isImmediateClass ifTrue:

[^0].

self primitiveFailed

byteSizeOfInstanceOfSize: basicSize

"Answer the total memory size of an instance of the receiver

with the given number of indexable instance variables."

<primitive: 181 error: ec>

self isVariable

ifTrue: "If the primitive overflowed answer a close approximation"

[(basicSize isInteger

and: [basicSize >= 16r1000000]) ifTrue:

[^2 * (self byteSizeOfInstanceOfSize: basicSize + 1 // 2)

- (self byteSizeOfInstanceOfSize: 0)]]

ifFalse:

[basicSize = 0 ifTrue:

[^self byteSizeOfInstance]].

self primitiveFailed

A small-integer is encoded in the pointer, so it has no size in itself, only the object
pointing to it needs space for the pointer, just like for normal object.

As are Characters, and in 64-bits the single-precision range of the double-precision floats:

{ SmallInteger maxVal sizeInMemory. (SmallInteger maxVal + 1) sizeInMemory. 1.0e38 sizeInMemory. 1.0e39 sizeInMemory. $a sizeInMemory }

in 64 bit is #(0 16 0 16 0)

in 32 bit is #(0 16 16 16 0)

The overflow header is revealed by

(251 to: 258) collect: [:n| (Array new: n) sizeInMemory]

in 64 bit is #(2016 2024 2032 2040 2056 2064 2072 2080)

in 32 bit is #(1016 1016 1024 1024 1040 1040 1048 1048)

_,,,^..^,,,_

best, Eliot

Marcus Denker-4

Re: Why 2017 sizeInMemory = 0?

#sizeInMemory only takes into account object header size and the size of the object
itself.

sizeInMemory is also ignorant of details such as the padding of objects to 64-bits in both 32-bit and 64-bit Spur, the overflow header when there are more than 254 slots, etc. siseInMemory should really be implemented like this:

Thanks, I added an issue tracker entry:

https://pharo.fogbugz.com/f/cases/20663/improve-sizeInMemory

Marcus