Re: [Caml-list] segmentation fault

[Julia Lawall <julia.lawall@lip6.fr>]

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On Tue, 20 Jun 2017, Francois BERENGER wrote:

> On 06/20/2017 06:19 AM, Julia Lawall wrote:
> >
> >
> > On Mon, 19 Jun 2017, Josh Berdine wrote:
> >
> > > On Mon, Jun 19 2017, Julia Lawall wrote:
> > >
> > > > On Mon, 19 Jun 2017, David MENTRÉ wrote:
> > > >
> > > > > Hello Julia,
> > > > >
> > > > > Le 2017-06-18 à 21:41, Julia Lawall a écrit :
> > > > > > Over several
> > > > > > runs on two different laptops, the backtraces have nothing obvious
> > > > > > in
> > > > > > common.  The bytecode version does not seem to stack overflow.
> > > > > > Adding
> > > > > > Gc.print_stat() at a periodic quiescent point in the execution did
> > > > > > not
> > > > > > show a memory leak.
> > > > >
> > > > > A similar issue related to random crash in native code version was
> > > > > asked
> > > > > by Alexey Egorov on this list 9 days ago. Daniel Bünzli advised to him
> > > > > to frequently call Gc.full_major () to have a crash closer to the real
> > > > > issue.
> > > >
> > > > OK, I will try this.
> > >
> > > Are you using Windows? I have only experienced segfaults from stack
> > > overflow on Windows.
> >
> > No, Linux.
> >
> > >
> > > > > In the case of Alexey, it was a non tail-recursive call that triggered
> > > > > a
> > > > > stack overflow and that is not detected in OCaml native code.
> > > > > Apparently
> > > > > this kind of issue is fixed in next to come OCaml 4.06.0.
> > > >
> > > > Why would something like this not be deterministic?  In my case, it can
> > > > happen after seconds or after tens of minutes.
> > >
> > > This sounds like an interaction with the GC to me.
> >
> > This was my thought as well.  Also, of the four cores I have, two are in
> > the Gc.  But two are not.
>
> If this is using parmap, I would suggest disabling parmap and trying a
> sequential version of the program.

Parmap is there, but there are tests to avoid calling it when only one
core is requested.

julia


>
> I have seen parmap "maskerading" exceptions.
> But when you don't use parmap, you can truly see what exception you have
> and where it is coming from.
>
> > > > > Of course, your issue might be entirely different. But frequently
> > > > > calling Gc.full_major () seems a sensible starting point to me.
> > > > >
> > > > > Otherwise you have the usual suspects: are you using C bidings?
> > > > > Threads?
> > > >
> > > > There are no threads.  The software may use C bindings.  I don't think
> > > > they are involved in the failing execution, but I'm not 100% sure.
> > >
> > > I have found running under valgrind to be helpful in this sort of
> > > situation, though it is slow and some valid code can trigger many
> > > warnings.
> >
> > OK, I'll try that.
> >
> > thanks,
> > julia
> >
> > >
> > > Cheers, Josh
> > >
> >
>
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