Re: [Caml-list] memory leak in toplevel? or, how to implement sizeof

[Jim Pryor <lists+caml@jimpryor.net>]

On Thu, Jan 06, 2011 at 09:44:06AM -0500, Jim Pryor wrote:
> Thanks David. So does this look like a reasonable implementation of
> sizeof:
> 
>     # let sizeof maker arg =
>         let first = Gc.((stat()).minor_words) in
>         let res = maker arg in
>         let second = Gc.((stat()).minor_words) in
>         int_of_float (second -. first) - 23 ( *overhead *), res;;
> 
>     # sizeof (fun x -> [x]) 1;;
>     - : int * int list = (3, [1])
> 
>     # sizeof (fun x -> Some x) 1;;
>     - : int * int option = (2, Some 1)
> 
> It does give the right answers. ([1] is a block containing two non-blocks; Some 1 is a block containing one non-block.)

Actually I think the overhead should be 22. Making it 22 gives these
sensible results:

    # sizeof (fun x -> x) 10;;
    - : int * int = (1, 10)

That is, one word for the int.

    # sizeof (fun x -> (x,()) ) 10;;
    - : int * (int * unit) = (4, (10, ()))

One word for the block pointer, one word for the block
header, one word for each of the two elements of the block.

    # sizeof (fun x -> (x,(x,())) ) 10;;
    - : int * (int * (int * unit)) = (7, (10, (10, ())))

Four words as above, one of them pointing to a new block, which contains
a header and two elements.

-- 
Jim Pryor
profjim@jimpryor.net