Periodic and cross platform timers or alarms

[Douglas Vechinski <douglas vechinski dynetics com>]

I have a GTK program in which I would like to periodically have a
function called (say every 1-5 sec) to perform a check on something and
take a certain action depending upon the result.  Usually the action
will be to do nothing and return.  I had first tried using a
gtk_idle_add but this calls it very frequently and eats a lot of cpu
time checking my "something" and sees that it hasn't changed so it
returns and does nothing only to be called practically right a way again
if the user isn't interacting with the interface.

Does GTK+ or GLIB provide any type of repeating timers or alarms?  I'm
looking for a portable way (Linux and XP).  Unix has "alarm" and XP has
other timers I believe but was looking for something that might be
common to both.