R help - Dec 2011 - Event handling in R

Dear R-helpers, 

I've just started playing with getGraphicsEvent() in R, and was wondering if
there is a simple way to stop this function waiting for input after a
pre-defined time, instead of relying either on a non-NULL value from one of the
event handlers or for a user-interrupt for it to halt (as per the R manual).

The only way that I've thought of to make this work is using setTimeLimit to
kill the function after a set time - here's a (messy) example:

setTimeLimit(cpu = 1)
plot(0, 0)
eventEnv <- getGraphicsEventEnv()
setGraphicsEventHandlers(prompt = 'Test')
while(TRUE) 
{
   err <- try(q <- getGraphicsEvent(), silent=TRUE)
   print(err)
}
# Not run
setTimeLimit(cpu = Inf)

but setTimeLimit doesn't seem to kill getGraphicsEvent() properly, as
running this code just ends up with the repeated returned error of "Error
in getGraphicsEvent(): recursive use of getGraphicsEvent not supported"
instead of the intended "Error: reached CPU time limit" every second.

Is there a way to get around this problem, or a different method to make this
work?  Or should I quit dabbling in things beyond my ken?


Thanks,
Nick

...because you're catching the timeout error with try() so it has not
effect, and hence the while(TRUE) {} loop keeps running.

Without knowing anything about graphics event handlers per se, here's
an alternative to catch the timeout event:

library("R.utils");

plot(0, 0);
eventEnv <- getGraphicsEventEnv();
setGraphicsEventHandlers(prompt='Test');

q <- NULL;
evalWithTimeout({
  q <- getGraphicsEvent();
}, timeout=1);
print(q);

does it.  See print(evalWithTimeout) to see what you are doing differently.

My $.02

/Henrik


On Thu, Dec 15, 2011 at 9:49 PM, beetonn <Nicholas.Beeton at utas.edu.au>
wrote:
> Dear R-helpers,
>
> I've just started playing with getGraphicsEvent() in R, and was
wondering if there is a simple way to stop this function waiting for input after
a pre-defined time, instead of relying either on a non-NULL value from one of
the event handlers or for a user-interrupt for it to halt (as per the R manual).
>
> The only way that I've thought of to make this work is using
setTimeLimit to kill the function after a set time - here's a (messy)
example:
>
> setTimeLimit(cpu = 1)
> plot(0, 0)
> eventEnv <- getGraphicsEventEnv()
> setGraphicsEventHandlers(prompt = 'Test')
> while(TRUE)
> {
> ? err <- try(q <- getGraphicsEvent(), silent=TRUE)
> ? print(err)
> }
> # Not run
> setTimeLimit(cpu = Inf)
>
> but setTimeLimit doesn't seem to kill getGraphicsEvent() properly, as
running this code just ends up with the repeated returned error of "Error
in getGraphicsEvent(): recursive use of getGraphicsEvent not supported"
instead of the intended "Error: reached CPU time limit" every second.
>
> Is there a way to get around this problem, or a different method to make
this work? ?Or should I quit dabbling in things beyond my ken?
>
>
> Thanks,
> Nick
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Thanks, Henrik! That's given me some food for thought, and evalWithTimeout
certainly seems to be a nicer way of doing this than setTimeLimit.

I should probably explain a little more clearly: I want to stop
getGraphicsEvent() without stopping the program flow (assume we're running
the code from a source file)  - hence the error catching in my example. If we
allow the exception through, it stops the program (which I don't want) but
stops getGraphicsEvent() properly, meaning we can run it again (which I do
want).

If we don't, the exception is caught and getGraphicsEvent() keeps running -
meaning we can't run it again without it throwing a recursion error.

To illustrate, if we set up with:

library(R.utils)
plot(0)
eventEnv <- getGraphicsEventEnv()
setGraphicsEventHandlers(prompt = 'Test')

and then 

while (TRUE) evalWithTimeout( {out <- getGraphicsEvent();}, timeout=1,
onTimeout="error")

it crashes out of the loop with a time-out error.

If we instead use 

while (TRUE) evalWithTimeout( {out <- getGraphicsEvent();}, timeout=1,
onTimeout="ignore")

it throws a recursion error after running getGraphicsEvent() for the second
time.



By the way, I may have found a bug in evalWithTimeout - there is a line

            else if (onTimeout == "silent") {

but "silent" is not one of the allowed arguments to the function. I
changed this to "ignore" and it seemed to work fine.


Cheers,
Nick

> ...because you're catching the timeout error with try() so it 
> has not
> effect, and hence the while(TRUE) {} loop keeps running.
> 
> Without knowing anything about graphics event handlers per se, here's
> an alternative to catch the timeout event:
> 
> library("R.utils");
> 
> plot(0, 0);
> eventEnv <- getGraphicsEventEnv();
> setGraphicsEventHandlers(prompt='Test');
> 
> q <- NULL;
> evalWithTimeout({
> q <- getGraphicsEvent();
> }, timeout=1);
> print(q);
> 
> does it. See print(evalWithTimeout) to see what you are 
> doing differently.
> 
> My $.02
> 
> /Henrik
> 
> On Thu, Dec 15, 2011 at 9:49 PM, beetonn 
> wrote:
> > Dear R-helpers,
> >
> > I've just started playing with getGraphicsEvent() in R, and 
> was wondering if there is a simple way to stop this function 
> waiting for input after a pre-defined time, instead of relying 
> either on a non-NULL value from one of the event handlers or for 
> a user-interrupt for it to halt (as per the R manual).
> >
> > The only way that I've thought of to make this work is using 
> setTimeLimit to kill the function after a set time - here's a 
> (messy) example:
> >
> > setTimeLimit(cpu = 1)
> > plot(0, 0)
> > eventEnv <- getGraphicsEventEnv()
> > setGraphicsEventHandlers(prompt = 'Test')
> > while(TRUE)
> > {
> > err <- try(q <- getGraphicsEvent(), silent=TRUE)
> > print(err)
> > }
> > # Not run
> > setTimeLimit(cpu = Inf)
> >
> > but setTimeLimit doesn't seem to kill getGraphicsEvent() 
> properly, as running this code just ends up with the repeated 
> returned error of "Error in getGraphicsEvent(): recursive use of 
> getGraphicsEvent not supported" instead of the intended "Error: 
> reached CPU time limit" every second.
> >
> > Is there a way to get around this problem, or a different 
> method to make this work? Or should I quit dabbling in things 
> beyond my ken?
> >
> >
> > Thanks,
> > Nick