memory leak in C snippet?

memory leak in C snippet?

[Lodewijk Voge]

hello,

I'm writing a daemon in ocaml with some glue code in C. it all works 
fine, except memory seems to leak to a point the daemon can last
only about a week on the smallest systems. after a lot of removing code 
I come to this snippet that seems to leak:

external bar: unit -> Unix.inet_addr * unit = "bar"

let _ =
         let s = String.create 392 in
         while true do
                 ignore(bar ());
         done

with

CAMLprim value bar(value unit) {
         CAMLparam1(unit);
         CAMLlocal2(res, addr);
         int i;

         addr = alloc_string(4);
         *(int *)(String_val(addr)) = htonl(0xac100000);
         res = alloc_tuple(2);
         Store_field(res, 0, addr);
         Store_field(res, 1, Val_unit);
         CAMLreturn(res);
}

which gives when run:

~/test$ while /usr/bin/true; do ps -o rss -p 15696 | tail -1; sleep 2; 
done
    784
    784
    788
    792
    796
    800
    804
    808
    812
^C

an ever growing RSS. strangely, having bar() return just the alloced 
string instead of a tuple, this doesn't occur. even more strangely, if 
I delete the let s = String.make 392 line, it doesn't occur either. 
systems tested are MacOS X, FreeBSD (the target system) and Linux. as 
the RSS approaches the segment size that'll expand too, and this 
gobbles up all available virtual memory in a week on the smallest 
target systems.

so, my question is: can anyone see an obvious error in the C snippet? 
some violation of the rules in the manual I missed?

thanks,
Lodewijk

Re: [Caml-list] memory leak in C snippet?

[Matthieu Brucher]

Hello

I'm not very into Ocaml at the moment, so perhaps what I will say isn't 
relevant, but you seem to allocate 2 memory blocs in your function 
(alloc_string and alloc_tuple), but where do you free this memory ? Does 
OCaml take charge of this or do you still have to do it yourself as it 
is in a C function ?
Happy new year.

Matthieu

Lodewijk Voge wrote:

> hello,
>
> I'm writing a daemon in ocaml with some glue code in C. it all works 
> fine, except memory seems to leak to a point the daemon can last
> only about a week on the smallest systems. after a lot of removing 
> code I come to this snippet that seems to leak:
>
> external bar: unit -> Unix.inet_addr * unit = "bar"
>
> let _ =
>         let s = String.create 392 in
>         while true do
>                 ignore(bar ());
>         done
>
> with
>
> CAMLprim value bar(value unit) {
>         CAMLparam1(unit);
>         CAMLlocal2(res, addr);
>         int i;
>
>         addr = alloc_string(4);
>         *(int *)(String_val(addr)) = htonl(0xac100000);
>         res = alloc_tuple(2);
>         Store_field(res, 0, addr);
>         Store_field(res, 1, Val_unit);
>         CAMLreturn(res);
> }
>
> which gives when run:
>
> ~/test$ while /usr/bin/true; do ps -o rss -p 15696 | tail -1; sleep 2; 
> done
>    784
>    784
>    788
>    792
>    796
>    800
>    804
>    808
>    812
> ^C
>
> an ever growing RSS. strangely, having bar() return just the alloced 
> string instead of a tuple, this doesn't occur. even more strangely, if 
> I delete the let s = String.make 392 line, it doesn't occur either. 
> systems tested are MacOS X, FreeBSD (the target system) and Linux. as 
> the RSS approaches the segment size that'll expand too, and this 
> gobbles up all available virtual memory in a week on the smallest 
> target systems.
>
> so, my question is: can anyone see an obvious error in the C snippet? 
> some violation of the rules in the manual I missed?
>
> thanks,
> Lodewijk



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Re: [Caml-list] memory leak in C snippet?

[Lodewijk Voge]

On 31-dec-04, at 10:35, Matthieu Brucher wrote:

> I'm not very into Ocaml at the moment, so perhaps what I will say 
> isn't relevant, but you seem to allocate 2 memory blocs in your 
> function (alloc_string and alloc_tuple), but where do you free this 
> memory ? Does OCaml take charge of this or do you still have to do it 
> yourself as it is in a C function ?

no, ocaml is supposed to do this. if it didn't, the daemon wouldn't 
last an hour, let alone a week :)

I think I'll file this as a bug and see what the gurus have to say 
about it. I'm staring myself silly at the code snippet and the manual 
and it's not helping.

Lodewijk

Re: [Caml-list] memory leak in C snippet?

[Jon Harrop]

On Friday 31 December 2004 09:35, Matthieu Brucher wrote:
> > CAMLprim value bar(value unit) {

What is the ocaml type of this function?

Cheers,
Jon.

Re: [Caml-list] memory leak in C snippet?

[Lodewijk Voge]

On 31-dec-04, at 16:10, Jon Harrop wrote:

>>> CAMLprim value bar(value unit) {
> What is the ocaml type of this function?

external bar: unit -> Unix.inet_addr * unit = "bar"

Lodewijk