Re: Recalculation of timeouts with g_timeout_add

[Luis Menina <liberforce freeside fr>]

Mitko Haralanov a écrit :
> On Fri, 16 May 2008 09:54:22 +0200
> G Hasse <gorhas raditex se> wrote:
>
> > Let your callback return FALSE and reregister before the return
>
> Hi, I thought of that but I was sure that there is a better way to do
> this without playing games with unregistering and re-registering the
> timeout.
>
> I am not sure why the GTK devs decided that re-calculating the timeout
> based on the time right after the timeout thread is started is the
> right thing to do but it seems very wrong to me. 

I think this is really the best solution. And by the way, this timeout 
comportment (counting elapsed time since last time the callback was 
called) is the right thing to do, as it's the most common case. Just 
because your current problem has different needs doesn't mean it was the 
wrong choice. How could you trigger an event, say, 10 times per second 
otherwise (for an animation for example) ?

> What if the timeout function takes longer then the timeout itself? You
> end up with multiple threads running the timeout function at the same
> time.

As already specified, there's only the main thread. GTK doesn't create 
other threads alone.

Oh, and you should use g_timeout_add_seconds for timeouts > 1s.

For your example, just set the timeout at the end of the callback, and 
return always FALSE. To set it the first time, just call the callback 
alone. That way the callback is called 20 seconds after the last 
callback call ended (I didn't tested the code, but it should work).

#include <gtk/gtk.h>
#include <glib.h>
#include <time.h>
#include <stdio.h>

gboolean callback (gpointer data) {
     int timeout = GPOINTER_TO_INT (data);
     printf ("callback called at: %lu\n", time (NULL));
     sleep (timeout);
     printf ("callback returns at: %lu\n", time (NULL));
     g_timeout_add_seconds (20, callback, GINT_TO_POINTER (timeout));
     return FALSE;
}

int main (int argc, char **argv) {
     int timeout = 10;
     gtk_init (&argc, &argv);
     callback (GINT_TO_POINTER (timeout);
     gtk_main ();
}



Also, you should give a look to GTimer, with is nice to use when you 
want to measure timings.


Cheers,

Luis