[R] mkChar can be interrupted

[Luke Tierney]

Not sure why you think this suggest mkChar can be interrupted.

If you want to figure out how interrupt handling works on unix, run
under gdb and single step from the signal to the next point where
R_CheckUserInterrupt is called.  You should find that the signal
handler sets a flag and that flag is checked at various safe points by
calls to this function.  I don't believe there are any such safe
points in mkChar, but there are several potential ones within your
example.

As mentioned in a reply in another thread, interrupt handling is one
aspect of R internals that is still evolving.  Among other things, we
will need to make changes as we improve support for other event loops.
[In applications with graphical interfaces signals are not the right
way to deal with user interruption (in particular on operating systems
that don't support proper signals)].

Best,

luke

On Mon, 14 Jun 2004, Vadim Ogranovich wrote:

> Hi,
>  
> As was discussed earlier in another thread and as documented in R-exts
> .Call() should not be interruptible by Ctrl-C. However the following
> code, which spends most of its time inside mkChar, turned out to be
> interruptible on RH-7.3 R-1.8.1 gcc-2.96:
>  
>  
> #include <Rinternals.h>
> #include <R.h>
> 
> SEXP foo0(const SEXP nSexp) {
>   int i, n;
>   SEXP resSexp;
> 
>   if (!isInteger(nSexp))
>     error("wrong arg type\n");
> 
>   n = asInteger(nSexp);
>   resSexp = PROTECT(allocVector(STRSXP, n));
>     
>   Rprintf("!!!time to interrup!!!\n");
>   for (i=0; i<n; ++i) {
>     SET_STRING_ELT(resSexp, i, mkChar("foo"));
>   }
> 
>   Rprintf("end mkChar\n");
>   UNPROTECT(1);
>     
>   return R_NilValue;
> }
> 
> 
> 
> # invoke 'foo0' and give it an argument large enough to let you type
> Ctrl-C
> # double the argument if you see "end mkChar" and do it again :-)
> > x <- .Call("foo0", as.integer(1e7))
> !!!time to interrup!!!
> 
> > 
> > version
>          _                
> platform i686-pc-linux-gnu
> arch     i686             
> os       linux-gnu        
> system   i686, linux-gnu  
> status                    
> major    1                
> minor    8.1              
> year     2003             
> month    11               
> day      21               
> language R                
> 
> 
> Thanks,
> Vadim
> 
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> 

-- 
Luke Tierney
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
   Actuarial Science
241 Schaeffer Hall                  email:      luke at stat.uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu