[R] Event handling in R

[Henrik Bengtsson]

...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
>
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