# How to measure an object size accurate **URL:** \ **Category:** Questions & Answers\ **Created:** [August 5, 2022, 8:41am UTC](https://racket.discourse.group/t/how-to-measure-an-object-size-accurate/1202 "2022-08-05T08:41:10Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![dannypsnl](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/dannypsnl/32/917_2.png) [@dannypsnl](https://racket.discourse.group/u/dannypsnl)\ **Post date:** [August 5, 2022, 8:41am UTC](https://racket.discourse.group/t/how-to-measure-an-object-size-accurate/1202/1 "2022-08-05T08:41:10Z")
I make a draft macro called `size` which takes an object and measures the memory use: ```scheme (define-syntax (size stx) (syntax-parse stx [(_ obj) #'(let ([before-use (current-memory-use)]) obj (define after-use (current-memory-use)) (printf "size: ~a bytes~n" (- after-use before-use)))])) (size (thread (λ () (let loop () (thread-receive) (loop))))) (size 1) (size 2) ``` Above program prints: ```scheme size: 8672 bytes size: 32 bytes size: 32 bytes ``` Does there any way to make it more accurate? ---
**Author:** ![jbclements](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/jbclements/32/11_2.png) [@jbclements](https://racket.discourse.group/u/jbclements)\ **Post date:** [August 5, 2022, 4:13pm UTC](https://racket.discourse.group/t/how-to-measure-an-object-size-accurate/1202/2 "2022-08-05T16:13:42Z")
First naive suggestion: call `(collect-garbage)` three times before measuring memory use. (The 3x may be a relic from the deep past, no idea if this is still the right heuristic.) ---
**Author:** ![jbclements](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/jbclements/32/11_2.png) [@jbclements](https://racket.discourse.group/u/jbclements)\ **Post date:** [August 5, 2022, 4:15pm UTC](https://racket.discourse.group/t/how-to-measure-an-object-size-accurate/1202/3 "2022-08-05T16:15:40Z")
Ooh... except that if the value doesn't survive, that call could actually collect it. So I would return it after checking the memory use, to make sure it doesn't die. Even then, you run the risk of optimizers cleverly discovering that it's not actually needed. ---
**Author:** ![jbclements](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/jbclements/32/11_2.png) [@jbclements](https://racket.discourse.group/u/jbclements)\ **Post date:** [August 5, 2022, 4:16pm UTC](https://racket.discourse.group/t/how-to-measure-an-object-size-accurate/1202/4 "2022-08-05T16:16:40Z")
but if you bind it to a top-level identifier, I would imagine that it definitely wouldn't get collected. ---
**Author:** ![gus-massa](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/gus-massa/32/507_2.png) [@gus-massa](https://racket.discourse.group/u/gus-massa)\ **Post date:** [August 5, 2022, 6:19pm UTC](https://racket.discourse.group/t/how-to-measure-an-object-size-accurate/1202/5 "2022-08-05T18:19:27Z")
With 8.2 CS, in DrRacket I got ``` size: 20112 bytes size: 0 bytes size: 0 bytes ``` My guess is 32 is the size of the temporal variables,. fixnums like `1` or `2` don't allocate memory neither in CS or BC. I made another version with `void/reference-sink` because otherwise the compiler may notice that it's unused and just avoid allocating it. (And there are a few more optimization that may remove the reference before you expect it.) For example try ``` (size (list 0 1 2 3 4 5 6 7 8 9)) ``` Also, I added `(sleep 1)`. I never heard it's necessary but trying the program a few times I get more consistent results with a small pause (???). With my version I get size that is like x10 the number I get with your version. ``` size: 182768 bytes size: 0 bytes size: 0 bytes ``` I'm not sure it's correct, but my version is: ``` #lang racket (require (for-syntax syntax/parse)) (require ffi/unsafe) (define-syntax (size stx) (syntax-parse stx [(_ obj) #'(let () (sleep 1) (collect-garbage) (collect-garbage) (collect-garbage) (define before-use (current-memory-use)) (define thing obj) (define after-use (current-memory-use)) (void/reference-sink thing) (printf "size: ~a bytes~n" (- after-use before-use)))])) (size (thread (λ () (let loop () (thread-receive) (loop))))) (size 1) (size 2) ``` ---
**Author:** ![dannypsnl](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/dannypsnl/32/917_2.png) [@dannypsnl](https://racket.discourse.group/u/dannypsnl)\ **Post date:** [August 6, 2022, 3:38am UTC](https://racket.discourse.group/t/how-to-measure-an-object-size-accurate/1202/6 "2022-08-06T03:38:49Z")
This sounds make sense, what I actually would like to know the representation size in machine of any value, but seems it only count the allocation ---
**Author:** ![jbclements](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/jbclements/32/11_2.png) [@jbclements](https://racket.discourse.group/u/jbclements)\ **Post date:** [August 7, 2022, 12:44pm UTC](https://racket.discourse.group/t/how-to-measure-an-object-size-accurate/1202/7 "2022-08-07T12:44:59Z")
You're pointing out that this doesn't measure the size of other existing values that are linked to from this one? So, for instance, in ```scheme (define a (list 3 4 5 6)) (define b (cons 44 a)) ``` You'd like the size of 'b' to include the size of 'a'? I don't see an easy way to compute this. I'm also not sure how useful it is, because it may include large values that are not collectible. I guess I should ask: how would you like to use this information? ---
**Author:** ![dannypsnl](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/dannypsnl/32/917_2.png) [@dannypsnl](https://racket.discourse.group/u/dannypsnl)\ **Post date:** [August 7, 2022, 3:48pm UTC](https://racket.discourse.group/t/how-to-measure-an-object-size-accurate/1202/8 "2022-08-07T15:48:53Z")
My original scenario is I have many long-live threads, they will exchange messages to complete different jobs, and each has its own local storage. I want to measure the accurate memory usage so that I can know the limitation of the design, to know whether I should add something into the thread or I should put them somewhere else. ---
**Author:** ![bogdan](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/bogdan/32/8_2.png) [@bogdan](https://racket.discourse.group/u/bogdan)\ **Post date:** [August 7, 2022, 7:00pm UTC](https://racket.discourse.group/t/how-to-measure-an-object-size-accurate/1202/9 "2022-08-07T19:00:18Z")
You may be able to use [current-memory-use](https://docs.racket-lang.org/reference/garbagecollection.html#%28def._%28%28quote._~23~25kernel%29._current-memory-use%29%29) with a custodian in that case. For example: ```scheme #lang racket/base (define cust (make-custodian)) (define thd (parameterize ([current-custodian cust]) (thread (lambda () (let loop ([data null]) (loop (cons (thread-receive) data))))))) (collect-garbage) (define old (current-memory-use cust)) (define (display-delta) (collect-garbage) (define new (current-memory-use cust)) (define delta (- new old)) (set! old new) (printf "delta: ~a~a old: ~a new: ~a~n" (if (> delta 0) "+" "") delta old new)) (display-delta) (thread-send thd (vector 1 2 3)) (display-delta) (thread-send thd (make-bytes 10240)) (display-delta) (thread-send thd (make-bytes 10240)) (display-delta) (define unreachable (make-bytes 10240)) (display-delta) (thread-send thd (make-bytes 10240)) (display-delta) ``` The above prints ```scheme delta: -32 old: 3472 new: 3472 delta: +104 old: 3576 new: 3576 delta: +10272 old: 13848 new: 13848 delta: +10272 old: 24120 new: 24120 delta: 0 old: 24120 new: 24120 delta: +10272 old: 34392 new: 34392 ``` on my machine with a recent build of Racket CS.