Hi Ben,

On 8 October 2012 at 15:15, Dirk Eddelbuettel wrote:
| 
| On 8 October 2012 at 10:21, Douglas Bates wrote:
| | On Mon, Oct 8, 2012 at 6:42 AM, Dirk Eddelbuettel <[email protected]> wrote:
| | >
| | > Hi Ben,
| | >
| | > On 8 October 2012 at 10:24, North, Ben wrote:
| | > | Hi,
| | > |
| | > | I've been using Rcpp for a while now, and finding it very useful ---
| | > | thanks!
| | > |
| | > | Recently, though, I came across strange behaviour when running under
| | > | gctorture(TRUE) and C++ exceptions were being forwarded to R.  The error
| | > | message string at the R level was some essentially random pathname, and
| | > | the string in the C++ exception was nowhere to be seen.  The classname
| | > | at the R level was the logical TRUE value.
| | > |
| | > | The patch below fixed the problem for me.  I would not claim to fully
| | > | know what I'm doing, so perhaps somebody who does could review and then
| | > | make the proper fix :-)
| | >
| | > It's been a while since we had something like this, and Doug lead it the 
last
| | > time. From what I recall, Rf_install() is safe, and the reason we factor
| | > these out as below. The bad boy, as I call, is probably Rf_mkString so by 
just doing
| | >
| | >  str_what  = Rf_install(exception_what.c_str());
| | >  str_class = Rf_install(exception_class.c_str());
| | >  str_ns    = Rf_install("Rcpp"));
| | >  Rf_eval(Rf_lang3(cppExceptSym, str_what, str_class), str_ns);
| | >
| | > may be enough.  Could you test that?
| | 
| | Just glancing quickly at this, I think it may or may not work.
| | Rf_install looks up a symbol in the symbol table, installing it if
| | needed, and returns the symbol SEXP.  Rf_mkstring creates a string
| | SEXP (vector of R class "character" containing a single string).  The
| | string probably needs protection.  The symbol does not.
| 
| Yes, that email was written too quickly.  There are some more instances in
| src/* where we do something similar, the Rf_eval is protected there too.

Could you test this simpler variant with one additional PROTECT?

        SEXP cppExceptExpr = PROTECT(Rf_lang3(cppExceptSym,
                                              
Rf_mkString(exception_what.c_str()), 
                                              
Rf_mkString(exception_class.c_str())));
        Rf_eval(cppExceptErr, R_FindNamespace(Rf_mkString("Rcpp"))); // Should 
not return. 

        // Do this in case somehow someone replaces the definition of
        // "cpp_exception" such that it does return:
        UNPROTECT(1);

I use some of the existing code in Rcpp/src/ as a guide -- we don't to
protect every Rf_mkString nor do we protect R_FindNamespace.

If the code above still fails in your setup, could try adding PROTECT
incrementally rather than en bloc ?

Thanks, Dirk
| 
| Dirk
|  
| | I imagine the R function cpp_exception expects strings.  I'm not sure
| | what happens if it gets symbols.
| | 
| | > |
| | > | Thanks,
| | > |
| | > | Ben.
| | > |
| | > | --- src/exceptions.cpp   2012-10-01 01:29:53.000000000 +0100
| | > | +++ ../Rcpp/src/exceptions.cpp     2012-10-08 11:14:39.435644100 +0100
| | > | @@ -161,14 +161,23 @@
| | > |                exception_class = name ; /* just using the mangled name 
*/
| | > |           }
| | > |      }
| | > | -    SEXP cppExceptSym = Rf_install("cpp_exception"); // cannot cause a 
gc() once in symbol table
| | > | -    Rf_eval(
| | > | -        Rf_lang3(
| | > | -         cppExceptSym,
| | > | -              Rf_mkString(exception_what.c_str()),
| | > | -              Rf_mkString(exception_class.c_str())
| | > | -         ), R_FindNamespace(Rf_mkString("Rcpp"))
| | > | -    ) ;
| | > | +
| | > | +    SEXP cppExceptSym;
| | > | +    SEXP str_what, str_class, str_ns, ns, expr;
| | > | +
| | > | +    PROTECT(cppExceptSym = Rf_install("cpp_exception"));
| | > | +    PROTECT(str_what = Rf_mkString(exception_what.c_str()));
| | > | +    PROTECT(str_class = Rf_mkString(exception_class.c_str()));
| | > | +    PROTECT(str_ns = Rf_mkString("Rcpp"));
| | > | +
| | > | +    PROTECT(ns = R_FindNamespace(str_ns));
| | > | +    PROTECT(expr = Rf_lang3(cppExceptSym, str_what, str_class));
| | > | +
| | > | +    Rf_eval(expr, ns); /* Should not return. */
| | > | +
| | > | +    // Do this in case somehow someone replaces the definition of
| | > | +    // "cpp_exception" such that it does return:
| | > | +    UNPROTECT(6);
| | > |  }
| | > |  #else
| | > |
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| | > --
| | > Dirk Eddelbuettel | [email protected] | http://dirk.eddelbuettel.com
| | > _______________________________________________
| | > Rcpp-devel mailing list
| | > [email protected]
| | > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
| 
| -- 
| Dirk Eddelbuettel | [email protected] | http://dirk.eddelbuettel.com  

-- 
Dirk Eddelbuettel | [email protected] | http://dirk.eddelbuettel.com  
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