[Rcpp-devel] Interrupts in compiled code.

[Douglas Bates]

On Wed, Dec 8, 2010 at 3:02 PM, Dirk Eddelbuettel <edd at debian.org> wrote:
>
> On 8 December 2010 at 13:41, Andrew Redd wrote:
> | I have an MCMC chain that runs entirely in c++ with Rcpp.  It sometimes runs
> | for a vary long time and I want to interrupt it.  Is there an efficient easy
> | way to include catching an interupt signal and either aborting or returning
> | results to that point?  This might be understood well, if so I apologize.
>
> Great question.
>
> Here is a simple example that uses a standard C interrupt handler to set a
> standard C++ exception to abort:
>
> ----------------------------------------------------------------
>
> #include <csignal>
> #include <Rcpp.h>
>
> void intHandler(int dummy=0) {
>  std::cerr << "In intHandler" << std::endl;
>  throw std::runtime_error("Interception caught");
> }

Gee, I wouldn't have pictured you as an American football fan.  I
think you meant "interrupt caught".

> RcppExport SEXP foo(void) {
>
>  try {
>
>    signal(SIGINT, intHandler);
>    signal(SIGKILL, intHandler);
>
>    while (true) {
>      sleep(1);                 // not doing much
>    }
>    return R_NilValue;
>
>  } catch(std::exception &ex) {
>    std::cerr << "In catch of std::exeception" << std::endl;
>    // here you insert some clenup
>    forward_exception_to_r(ex);
>
>  } catch(...) {
>    ::Rf_error("c++ exception (unknown reason)");
>  }
>
>  return R_NilValue;
> }
>
> ----------------------------------------------------------------
>
> which I then quickly turned into a shared object, load and ran at the
> command-line [1]
>
> edd at max:/tmp/andrew$ PKG_CPPFLAGS=`r -e'Rcpp:::CxxFlags()'` PKG_LIBS=`r -e'Rcpp:::LdFlags()'` R CMD SHLIB int2throw.cpp
> ccache g++ -I/usr/share/R/include -I/usr/local/lib/R/site-library/Rcpp/include     -fpic  -g -O3 -Wall -pipe -pedantic -Wno-variadic-macros -c int2throw.cpp -o int2throw.o
> g++ -shared -o int2throw.so int2throw.o -L/usr/local/lib/R/site-library/Rcpp/lib -lRcpp -Wl,-rpath,/usr/local/lib/R/site-library/Rcpp/lib -L/usr/lib64/R/lib -lR
> edd at max:/tmp/andrew$ r -e'dyn.load("int2throw.so"); .Call("foo")'
> ^CIn intHandler
> In catch of std::exeception
> Error in cpp_exception(message = "Interception caught", class = "std::runtime_error") :
>  Interception caught
> Execution halted
> edd at max:/tmp/andrew$
> edd at max:/tmp/andrew$
>
>
> After lauching it from the one-line littler (r) expression, I pressed Ctrl-C
> which then got us into the interrupt which threw the exception which lead to
> the end.
>
> In Rscript it looks a little more orderly on the unwind:
>
> edd at max:/tmp/andrew$ Rscript -e 'dyn.load("int2throw.so"); .Call("foo")'
>  C-c C-cIn intHandler
> In catch of std::exeception
> Error in cpp_exception(message = "Interception caught", class = "std::runtime_error") :
>  Interception caught
> Calls: .Call -> cpp_exception
> Execution halted
> edd at max:/tmp/andrew$
>
>
> Hope this helps,  Dirk
>
>
> [1] Not sure why I didn't use inline today...
>
>
> --
> Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
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