[Rcpp-devel] Missing PROTECT()s in forward_exception_to_r()?

[Dirk Eddelbuettel]

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?

Dirk

| 
| 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 | edd at debian.org | http://dirk.eddelbuettel.com