marionnet-dev team mailing list archive

[Luca Saiu <positron@xxxxxxx>]

Hello.

On 2014-06-19 at 18:20, noreply@xxxxxxxxxxxxx wrote:

>   Fixed a possible very critical memory leak introduced in revno
> 388. The problem was occurring in a thread calling the function
> Linux.process.stat' repetitively in a loop. Strangely, the source of
> the problem seems to be the standard function `Scanf.fscanf'. In a way
> that I don't understand, `fscanf' seems able to get the GC confused:
> unused `Linux.process.stat' structures are indeed not collected (even
> forcing a collection with Gc.full_major). The workaround adopted
> consists in replacing `Scanf.fscanf ch' by a `Scanf.sscanf line' where
> line' is read from `ch' by `Pervasives.input_line'. Now `stat'
> structures seem to be correctly collected.

Interesting.

As a guess without looking at OCaml runtime source code, I'd suspect
this to be a buffering issue in fscanf, which gobbles up a large memory
buffer as an OCaml string without releasing it, with the intent of
reusing it for the next read operation.  By contrast sscanf takes a
string as a parameter which is explicitly supplied by the user, and when
that gets unreachable it immediately becomes a candidate for collection.
Are you reading very large strings?

Very good catch anyway :-).  This must not have been easy to isolate.

-- 
Luca Saiu      http://ageinghacker.net
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