OCaml memory leak issue

OCaml memory leak issue

[Kecheng]

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Hi,

I used valgrind to check the memory usage of my OCaml byte code, but I found that a memory leak. I'm very confused what the problem is. I tried a very simple code as following, and compileed it. 

+++++++++++++++++++++++
let test  = 
    let a = 1 in
    let b = a + 5 in
    printf "%d\n" b;
;;
test;;
+++++++++++++++++++++++

And I run valgrind to check: 

valgrind --leak-check=yes ./obj/x86_LINUX/test5.byte.exe 

I got the following report:
==21692== Memcheck, a memory error detector
==21692== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==21692== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info
==21692== Command: ./obj/x86_LINUX/test5.byte.exe
==21692==
6
==21692==
==21692== HEAP SUMMARY:
==21692==     in use at exit: 430,488 bytes in 20 blocks
==21692==   total heap usage: 68 allocs, 48 frees, 446,837 bytes allocated
==21692==
==21692== 120 bytes in 1 blocks are definitely lost in loss record 9 of 17
==21692==    at 0x4A05E1C: malloc (vg_replace_malloc.c:195)
==21692==    by 0x9AA510: caml_init_major_heap (in /home/kecheng/symbolic_simulation/cvc_test/cvc_1.5/obj/x86_LINUX/test5.byte.exe)
==21692==    by 0x9A2A1A: caml_init_gc (in /home/kecheng/symbolic_simulation/cvc_test/cvc_1.5/obj/x86_LINUX/test5.byte.exe)
==21692==    by 0x997E9D: caml_main (in /home/kecheng/symbolic_simulation/cvc_test/cvc_1.5/obj/x86_LINUX/test5.byte.exe)
==21692==    by 0x9981CB: main (in /home/kecheng/symbolic_simulation/cvc_test/cvc_1.5/obj/x86_LINUX/test5.byte.exe)
==21692==
==21692== LEAK SUMMARY:
==21692==    definitely lost: 120 bytes in 1 blocks
==21692==    indirectly lost: 0 bytes in 0 blocks
==21692==      possibly lost: 0 bytes in 0 blocks
==21692==    still reachable: 430,368 bytes in 19 blocks
==21692==         suppressed: 0 bytes in 0 blocks
==21692== Reachable blocks (those to which a pointer was found) are not shown.
==21692== To see them, rerun with: --leak-check=full --show-reachable=yes
==21692==
==21692== For counts of detected and suppressed errors, rerun with: -v
==21692== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)




Kecheng
2010-11-23

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Re: [Caml-list] OCaml memory leak issue

[Edgar Friendly]

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On 11/23/2010 07:54 PM, Kecheng wrote:
> let test  =
>     let a = 1 in
>     let b = a + 5 in
>     printf "%d\n" b;
> ;;
> test;;
This will finish with a bunch of allocated memory missing pointers to 
it.  But that's not a problem, because OCaml's GC is capable of freeing 
this memory, as opposed to a C program, which would need a pointer to 
the memory to free() it.

E.

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Re: [Caml-list] OCaml memory leak issue

[Török Edwin]

On Tue, 23 Nov 2010 19:54:24 -0800
"Kecheng" <kecheng@cecs.pdx.edu> wrote:

> Hi,
> 
> I used valgrind to check the memory usage of my OCaml byte code, but
> I found that a memory leak. I'm very confused what the problem is. I
> tried a very simple code as following, and compileed it. 
> 
> +++++++++++++++++++++++
> let test  = 
>     let a = 1 in
>     let b = a + 5 in
>     printf "%d\n" b;
> ;;
> test;;
> +++++++++++++++++++++++

I think you need to call the GC on exit explicitly, its not done by
default.

Best regards,
--Edwin

Re: [Caml-list] OCaml memory leak issue

[Goswin von Brederlow]

Török Edwin <edwintorok@gmail.com> writes:

> On Tue, 23 Nov 2010 19:54:24 -0800
> "Kecheng" <kecheng@cecs.pdx.edu> wrote:
>
>> Hi,
>> 
>> I used valgrind to check the memory usage of my OCaml byte code, but
>> I found that a memory leak. I'm very confused what the problem is. I
>> tried a very simple code as following, and compileed it. 
>> 
>> +++++++++++++++++++++++
>> let test  = 
>>     let a = 1 in
>>     let b = a + 5 in
>>     printf "%d\n" b;
>> ;;
>> test;;
>> +++++++++++++++++++++++
>
> I think you need to call the GC on exit explicitly, its not done by
> default.
>
> Best regards,
> --Edwin

Correct. Ocaml assumes (or knows which OS does) the OS will free all
resource at exit anyway. No point wasting valuable time doing a GC
sweep.

In case of custom blocks and finalize function I believe this to be an
error. Managing resources that the OS does not free (IPC tokens,
tempfiles, ...) is made much harder due to this.

MfG
        Goswin

Re: [Caml-list] OCaml memory leak issue

[DS]

On 24 Nov 2010, at 23:40, Goswin von Brederlow wrote:
> In case of custom blocks and finalize function I believe this to be an
> error. Managing resources that the OS does not free (IPC tokens,
> tempfiles, ...) is made much harder due to this.
But you can force a final GC run with Pervasives.at_exit Gc.full_major.
Regards.
-DS

Re: [Caml-list] OCaml memory leak issue

[Goswin von Brederlow]

DS <ds.caml@sol42.com> writes:

> On 24 Nov 2010, at 23:40, Goswin von Brederlow wrote:
>> In case of custom blocks and finalize function I believe this to be an
>> error. Managing resources that the OS does not free (IPC tokens,
>> tempfiles, ...) is made much harder due to this.
> But you can force a final GC run with Pervasives.at_exit Gc.full_major.
> Regards.
> -DS

But you can't force global variables to be freeed. Imho it would be nice
to have a GC setting where one could tell the runtime to free
everything, including global variables, before it exits.

MfG
        Goswin

Re: [Caml-list] OCaml memory leak issue

[Christophe TROESTLER]

On Wed, 24 Nov 2010 23:40:03 +0100, Goswin von Brederlow wrote:
> 
> In case of custom blocks and finalize function I believe this to be an
> error. Managing resources that the OS does not free (IPC tokens,
> tempfiles, ...) is made much harder due to this.

You also have "at_exit" and weak pointers which can help you to do that.

Best,
C.