[R] mkChar can be interrupted

[Vadim Ogranovich]

> -----Original Message-----
> From: Luke Tierney [mailto:luke at stat.uiowa.edu] 
> Sent: Monday, June 14, 2004 1:30 PM
> To: Vadim Ogranovich
> Cc: R-Help
> Subject: Re: [R] mkChar can be interrupted
> 
> 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.

Apart from mkChar I am only calling SET_STRING_ELT. Is this what you
mean?

To make sure, I am not trying to enable or handle interrupts. On the
contrary, I want them to be disabled for the duration of .Call, which is
what I thought R was supposed to do for me. I am surprised it didn't.

As to why I singled out mkChar, well, strictly speaking it is
'SET_STRING_ELT(resSexp, i, mkChar("foo"))' where the interrupt somehow
goes through. But SET_STRING_ELT is much faster than mkChar so I guessed
that it must be mkChar.
Anyway, be it SET_STRING_ELT or mkChar, the interrupt should have been
blocked.


As an additional check I tried to interrupt right before and right after
  for (i=0; i<n; ++i) {
    SET_STRING_ELT(resSexp, i, mkChar("foo"));
  }
but the interrupt was rightfully blocked.


I understand that .Call blocks interrupts, but it seems that very
primitive functions like SET_STRING_ELT, mkChar can decide to handle
them. This is surprising and I think my conjecture is wrong, but how
else to explain that I was able to interrupt 'foo0'?

Thanks,
Vadim

> 
> 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
> > 
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide! 
> > http://www.R-project.org/posting-guide.html
> > 
> 
> --
> 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
> 
> 
>