[Rcpp-devel] "Error during wrapup"

[Romain Francois]

Le 29 mai 2014 à 00:35, John Mous <john.mous0 at gmail.com> a écrit :

> No luck with gctorture on yet, but I haven't run it for very long. It slowed things down to a complete crawl, but maybe in the long run it can recreate the problem faster than running the original code (about 12 hours, the previous estimate of a day was too high), so this may still be worthwhile. 
> 
> On a whim I did try changing the two instances of Shield to Armor this morning (I was able to locate the code in wrap.h by digging around before I saw your e-mail) and ran the original full code without gctorture on, and the problem still persists. 

Would not be enough, you'd also have to do: 

x = ::Rf_setAttrib( x, R_NamesSymbol, names ) ;

so that the result of setAttrib gets protected even if it is a new SEXP, which AFAIU can happen with setAttrib. 

But I'm not sure this is the problem. 

Romain

> 
> On Wed, May 28, 2014 at 3:44 PM, Romain Francois <romain at r-enthusiasts.com> wrote:
> (now with some links):
> 
> Le 28 mai 2014 à 16:31, John Mous <john.mous0 at gmail.com> a écrit :
> 
>> The object really is just built as part of the return statement. i.e. the lines from my prior e-mail exist as-is in the full code,
> 
> Sure. What happens is that Rcpp::export generates something that calls wrap( std::map<std::string,int> ). 
> 
>> there's just more that actually builds the variables X1-X4 beforehand.
> 
> It should not be relevant. 
> 
>> So I'm not sure where to debug from the client side. I'm a C/C++ developer, but have no experience with Rcpp internals or the general interface between R and C. I can insert some debug statements on the Rcpp side if you can guide me to where wrap is defined. 
> 
> well wrap is defined here: 
> https://github.com/RcppCore/Rcpp/blob/master/inst/include/Rcpp/internal/wrap_end.h#L28
> 
> It then performs a series of dispatch, that eventually lead to something that handles std::map<std::string,int>: 
> https://github.com/RcppCore/Rcpp/blob/master/inst/include/Rcpp/internal/wrap.h#L255
> 
> 
> template <typename InputIterator, typename T>
> 
> inline SEXP range_wrap_dispatch___impl__cast( InputIterator first, InputIterator last, ::Rcpp::traits::false_type ){
> 
> 	size_t size = std::distance( first, last ) ;
> 
> 	const int RTYPE = ::Rcpp::traits::r_sexptype_traits<typename T::second_type>::rtype ;
> 
> 	Shield<SEXP> x( Rf_allocVector( RTYPE, size ) );
> 
> 	Shield<SEXP> names( Rf_allocVector( STRSXP, size ) ) ;
> 
> 	typedef typename ::Rcpp::traits::storage_type<RTYPE>::type CTYPE ;
> 
> 	CTYPE* start = r_vector_start<RTYPE>(x) ;
> 
> 	size_t i =0;
> 
> 	std::string buf ;
> 	for( ; i<size; i++, ++first){
> 
> 		start[i] = (*first).second ;
> 
> 		buf = (*first).first ;
> 
> 		SET_STRING_ELT( names, i, Rf_mkChar(buf.c_str()) ) ;
> 
> 	}
> 	::Rf_setAttrib( x, R_NamesSymbol, names ) ;
> 
> 	return wrap_extra_steps<T>( x ) ;
> 
> }
> 
> what I suspect to be the problem is this line:
> 
>  ::Rf_setAttrib( x, R_NamesSymbol, names ) ;
> 
> 
>> What Romain says makes sense to me, despite my lack of expertise in this area.. the really intermittent nature of the problem and the fact that I can't recreate it in a small / fast running example suggests that perhaps this manifests when R happens to garbage collect at an unfortunate time (if I understood correctly). Thanks again.
> 
> Something like that. as hadley hinted, please try this under gc torture, or preferably through a debugger. 
> 
>> On Wed, May 28, 2014 at 10:12 AM, Dirk Eddelbuettel <edd at debian.org> wrote:
>> 
>> On 28 May 2014 at 10:02, John Mous wrote:
>> | Hmm, unfortunately the GitHub version failed also.
>> 
>> Darn.
>> 
>> | The attributes on the failed
>> | object are a little different though, here's what they look like:
>> |
>> | Browse[1]> str(results)
>> |  atomic [1:4] 1 1 2270 0
>> |  - attr(*, "")= symbol sim
>> |  - attr(*, "value")= promise to  NULL
>> 
>> I am not sure what we can do without a reproducible example. :-/
>> The code just got a review / refreshment over the last few months.
>> 
>> You best bet may the slow and tedious insertion of debug statements to see
>> when / if the object changes.
>> 
>> Dirk
>> 
>> --
>> Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
>> 
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> 
> 

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