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Gtk+/Gnome Application Development
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Idle Functions

Idle functions run continuously while the GTK+ main loop has nothing else to do. Idle functions run only when the event queue is empty and the main loop would normally sit idly, waiting for something to happen. As long as they return TRUE they are invoked over and over; when they return FALSE, they are removed, just as if gtk_idle_remove() had been called.

The idle function API, shown in Figure 31, is identical to the timeout and quit function APIs. Again, gtk_idle_remove() should not be called from within an idle function, because it will corrupt GTK+'s idle function list. Return FALSE to remove the idle function.

Idle functions are mostly useful to queue "one-shot" code, which is run after all events have been handled. Relatively expensive operations such as GTK+ size negotiation and GnomeCanvas repaints take place in idle functions that return FALSE. This ensures that expensive operations are performed only once, even though multiple consecutive events independently request the recalculation.

The GTK+ main loop contains a simple scheduler; idle functions actually have priorities assigned to them, just as UNIX processes do. You can assign a non-default priority to your idle functions, but it's a complicated topic outside the scope of this book.

#include <gtk/gtkmain.h>

guint gtk_idle_add(GtkFunction function, gpointer data);

void gtk_idle_remove(guint idle_handler_id);

void gtk_idle_remove_by_data(gpointer data);

Figure 31. Idle Functions

Gtk+/Gnome Application Development
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