[Rcpp-devel] experimental handling of uncaught exceptions

[Romain François]

On 12/28/2009 10:58 AM, Romain François wrote:
> On 12/27/2009 09:03 PM, Dirk Eddelbuettel wrote:
>>
>> On 27 December 2009 at 13:36, Dirk Eddelbuettel wrote:
>> | On 27 December 2009 at 18:15, Romain François wrote:
>> | | Hi,
>> | |
>> | | I've commited some code that aims at forwarding uncaught C++
>> exceptions
>> | | to R.
>> | |
>> | | For example :
>> | |
>> | | require( Rcpp)
>> | | funx<- cfunction(signature(), '
>> | | throw std::range_error("boom") ;
>> | | return R_NilValue ;
>> | | ', Rcpp=TRUE, verbose=FALSE)
>> | | tryCatch( funx(), "C++Error" = function(e){
>> | | print( "gotcha" )
>> | | } )
>> | | print( rnorm(10) )
>> |
>> | That's pretty crazy cool -- I'll have to try that.
>>
>> Can we get access to the string 'boom' at the R level?
>
> I am not sure. I think we cannot. I would also like to reach the class
> of the exception "range_error" to bring direct handlers (once again the
> idea is rJava inspired) but this does not seem possible.
>
> If C++ had reflection, then this would be possible;
>
> tryCatch( funx(), range_error = function(e){
> # do something with the range error exception
> } )
>
> This does not aim to replace explicit try/catch within the code, but it
> prevents the R session from crashing if some exception is not caught.

Some random browsing brings some hope here:
- http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt02ch06s02.html
- 
http://doc.infopac.ru/C,C++/libstdc++-html-USERS-3.3/vterminate_8cc-source.html

Also learned about the abi namespace (which is supposed to be 
cross-compiler) which brings some level of demangling capabilities :
- http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt12ch39.html

Not sure what I want to make of this.

>> That's how the
>> existing C++-based try/catch -> Rf_error() works.
>
> For this I thought that maybe we could have an "r_error" exception, with
> an overloaded throw operator so that we would do :
>
> throw r_error( "boom" ) ;
>
>> Also, the onAttach trick won't work for other packages just including
>> Rcpp.h
>> et al and linking to libRcpp.{so,a}.
>
> These packages can just call "initUncaughtExceptionHandler" from their
> C++ side, this is the only thing the .onAttach does.
>
> Now the mechanism calls back an R function that lives (and is not
> exported from) the Rcpp namespace.
>
> uncaught_cpp_exception <- function( message = "uncaught C++ exception" ){
> callstack <- sys.calls()
> ncalls <- length(callstack)
> call <- if( ncalls > 1L) callstack[[ ncalls - 1L ]] else match.call()
> classes <- c( "C++Error", "error", "condition" )
> condition <- structure(
> list( message = message, call = call ),
> class = classes )
> stop( condition )
> }
>
> Are there cases where the libRcpp.{so,a} is used but the Rcpp package is
> not available ?
>
> We could have it all in C, but this leads to more complicated code. See
> the file rJava.c attached for how Simon does it in rJava. (look between
> hack and hack)
>
>> Dirk

-- 
Romain Francois
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http://romainfrancois.blog.free.fr
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