[Rcpp-devel] (Very) rare segfault

[Romain Francois]

Ah interesting. PutRNGstate does indeed allocate so might trigger GC. 
https://github.com/wch/r-source/blob/fbf5cdf29d923395b537a9893f46af1aa75e38f3/src/main/RNG.c#L437

That's a whole new Pandora's box right there. 

Le 21 août 2014 à 12:10, Matteo Fasiolo <matteo.fasiolo at gmail.com> a écrit :

> Hi Romain and Gregor,
> 
> maybe I am misunderstanding everything, but hasn't this problem been explained and solved here:
> 
> http://lists.r-forge.r-project.org/pipermail/rcpp-devel/2013-May/005838.html
> 
> Best,
> 
> Matteo
> 
>  
> 
> 
> On Thu, Aug 21, 2014 at 10:58 AM, Romain Francois <romain at r-enthusiasts.com> wrote:
> 
> Le 21 août 2014 à 11:47, Gregor Kastner <gregor.kastner at wu.ac.at> a écrit :
> 
> > On Thu, 21 Aug 2014 11:34:23 +0200
> > Romain Francois <romain at r-enthusiasts.com> wrote:
> >
> > GK> Yep, sorry for the misuse of language. And I do understand going back to
> > GK> GetRNGstate() and PutRNGstate() is a bit old school; but I can definitely
> > GK> confirm that it seems to be safer than resorting do the
> > GK> constructor/destuctor magic.
> >>
> >> Compiler/Destructor is not magic. It is determinism.
> >>
> >> That's like feature #1 of C++.
> >
> > agreed: s/magic/automagic/g
> >
> >> And BTW it is definitely safer than any manual handling.
> >
> > I cannot say that in the current case, as relying on the destructor does seem
> > to create problems (in rare cases, making it even worse!) if objects which
> > are to be returned are instantiated after the RNGScope object. Conditional on
> > the fact the I understood JJ correctly, that is.
> 
> Then it's a bug in how constructor or destructor is implemented in this class, probably with the counter.
> 
> Or something invalidates the very assumptions of C++ here. Perhaps raw R api is called and the destructor is not called because of some long jump or something.
> 
> Without a repex anyway, it is hard to diagnose what's happening.
> 
> You're probably onto somthing, but going directly to the "destructor are not safe, I'll just use C function calls" is a dangerous route, soon you'll start using SEXP as you won't trust ctors/dtors of Rcpp objects do the right thing.
> 
> > Manual handling works perfectly.
> >
> > Best,
> > /g
> 
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