[Rd] interrupting R from a GUI

[Prof Brian Ripley]

On Fri, 16 Jan 2009, Felix Andrews wrote:

> list(...),
>
> I am looking for a way to interrupt R from a callback: specifically,
> to interrupt plotting (typically on a cairoDevice, but would be good
> if it worked with other devices too). Of course, one can interrupt R
> nicely from the console with Ctrl-C (or Esc in Rgui), but I need to do
> it from a GUI. Callbacks run in a new thread, so obviously stop() etc
> will not work. I tried to look into how Rgui does it...
> https://svn.r-project.org/R/trunk/src/gnuwin32/psignal.c

Actually no, Rgui does not use that code (but Rterm does).

> ?...but it is beyond me.

In detail this is OS-specific, but what the front-ends do is to set a 
flag or send a signal to R: look e.g. at rterm.c:

static void my_onintr(int nSig)
{
   UserBreak = 1;
   PostThreadMessage(mainThreadId,0,0,0);
}

or onintr in errors.c (which is called when UserBreak = 1, from the 
ain thread).  In due course R_interrupts_pending gets set and then at 
an appropriate spot R stops and unwinds the currrent evaluations.

The relevant Windows code is even in 'Writing R Extensions'.

So depending on your OS you can raise a signal or set a flag.  You can 
raise a signal on Windows too, so 'raise' is the most portable 
solution -- but beware that threading models differ.

> Alternatively, might there be a way to tell the cairoDevice widget to
> stop drawing, somehow?

Why not ask its author?

> Any help would be appreciated.
>
> -Felix
>
> --
> Felix Andrews / 安福立
> http://www.neurofractal.org/felix/

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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/‾ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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