Regularize main loop priorities

If there is a client that is continually redrawing, then
sources that are less-prioritized than CLUTTER_PRIORITY_REDRAW
will never get run. This patch sorts out how all the different
main loop sources fit in CLUTTER_PRIORITY_REDRAW.

common.h: Document all the relevant priorities and how they
  fit in with each other.
ui.h common.h: Move META_PRIORITY_RESIZE to to common.h with
  other priorities.
src/core/window.c src/core/screen.c: Change calc-showing,
  update-icon, and update-work-area idles to be prioritized above
  redraws so they don't get starved.
bell.c: Make the visual bell priority the same as the clutter
  redraw priority.
delete.c: Use a G_PRIORITY_DEFAULT idle when responding to the
  dialog response; we want to handle it as soon as practical.

http://bugzilla.gnome.org/show_bug.cgi?id=568874

src/core/bell.c

@@ -210,7 +210,12 @@ bell_flash_window_frame (MetaWindow *window)
   g_assert (window->frame != NULL);
   window->frame->is_flashing = 1;
   meta_frame_queue_draw (window->frame);
-  g_timeout_add_full (G_PRIORITY_DEFAULT_IDLE, 100, 
+  /* Since this idle is added after the Clutter clock source, with
+   * the same priority, it will be executed after it as well, so
+   * we are guaranteed to get at least one frame drawn in the
+   * flashed state, no matter how loaded we are.
+   */
+  g_timeout_add_full (META_PRIORITY_REDRAW, 100, 
       bell_unflash_frame, window->frame, NULL);
 }
 

src/core/delete.c

@@ -71,7 +71,8 @@ sigchld_handler (MetaNexus *nexus, guint arg1, gpointer arg2, gpointer user_data
   if (GPOINTER_TO_INT (arg2) == ours->dialog_pid)
     {
       if (arg1 == 1 /* pressed "force quit" */)
-        g_idle_add (delete_window_callback, user_data);
+        g_idle_add_full (G_PRIORITY_DEFAULT,
+                         delete_window_callback, user_data, NULL);
 
       ours->dialog_pid = -1; /* forget it anyway */
     }

src/core/screen.c

@@ -2115,7 +2115,7 @@ meta_screen_queue_workarea_recalc (MetaScreen *screen)
       meta_topic (META_DEBUG_WORKAREA,
                   "Adding work area hint idle function\n");
       screen->work_area_idle =
-        g_idle_add_full (META_PRIORITY_WORK_AREA_HINT,
+        g_idle_add_full (META_PRIORITY_BEFORE_REDRAW,
                          (GSourceFunc) set_work_area_idle_func,
                          screen,
                          NULL);

src/core/window.c

@@ -1987,9 +1987,9 @@ meta_window_queue (MetaWindow *window, guint queuebits)
 
           const gint window_queue_idle_priority[NUMBER_OF_QUEUES] =
             {
-              G_PRIORITY_DEFAULT_IDLE,  /* CALC_SHOWING */
+              META_PRIORITY_BEFORE_REDRAW, /* CALC_SHOWING */
-              META_PRIORITY_RESIZE,     /* MOVE_RESIZE */
+              META_PRIORITY_RESIZE,        /* MOVE_RESIZE */
-              G_PRIORITY_DEFAULT_IDLE   /* UPDATE_ICON */
+              META_PRIORITY_BEFORE_REDRAW  /* UPDATE_ICON */
             };
 
           const GSourceFunc window_queue_idle_handler[NUMBER_OF_QUEUES] =

src/include/common.h

@@ -287,8 +287,57 @@ struct _MetaButtonLayout
 
 #define META_DEFAULT_ICON_NAME "window"
 
+/* Main loop priorities determine when activity in the GLib
+ * will take precendence over the others. Priorities are sometimes
+ * used to enforce ordering: give A a higher priority than B if
+ * A must occur before B. But that poses a problem since then
+ * if A occurs frequently enough, B will never occur.
+ *
+ * Anything we want to occur more or less immediately should
+ * have a priority of G_PRIORITY_DEFAULT. When we want to
+ * coelesce multiple things together, the appropriate place to
+ * do it is usually META_PRIORITY_BEFORE_REDRAW.
+ *
+ * (FIXME: Use a Clutter paint() function instead, to prevent
+ * starving the repaints)
+ *
+ * If something has a priority lower than the redraw priority
+ * (such as a default priority idle), then it may be arbitrarily
+ * delayed. This happens if the screen is updating rapidly: we
+ * are spending all our time either redrawing or waiting for a
+ * vblank-synced buffer swap. (When X is improved to allow
+ * clutter to do the buffer-swap asychronously, this will get
+ * better.)
+ */
+
+/* G_PRIORITY_DEFAULT:
+ *  events
+ *  many timeouts
+ */
+
+/* GTK_PRIORITY_RESIZE:         (G_PRIORITY_HIGH_IDLE + 10) */
+#define META_PRIORITY_RESIZE    (G_PRIORITY_HIGH_IDLE + 15)
+/* GTK_PRIORITY_REDRAW:         (G_PRIORITY_HIGH_IDLE + 20) */
+
+#define META_PRIORITY_BEFORE_REDRAW  (G_PRIORITY_HIGH_IDLE + 40)
+/*  calc-showing idle
+ *  update-icon idle
+ */
+
+/* CLUTTER_PRIORITY_REDRAW:     (G_PRIORITY_HIGH_IDLE + 50) */
+#define META_PRIORITY_REDRAW    (G_PRIORITY_HIGH_IDLE + 50)
+
+/* ==== Anything below here can be starved arbitrarily ==== */
+
+/* G_PRIORITY_DEFAULT_IDLE:
+ *  Mutter plugin unloading
+ *  GConf notify idle
+ */
+
+/* Chosen to be below the GConf notify idle */
 #define META_PRIORITY_PREFS_NOTIFY   (G_PRIORITY_DEFAULT_IDLE + 10)
-#define META_PRIORITY_WORK_AREA_HINT (G_PRIORITY_DEFAULT_IDLE + 15)
+
+/************************************************************/
 
 #define POINT_IN_RECT(xcoord, ycoord, rect) \
  ((xcoord) >= (rect).x &&                   \

src/include/ui.h

@@ -31,9 +31,6 @@
 #include <glib.h>
 #include <gdk-pixbuf/gdk-pixbuf.h>
 
-/* This is between GTK_PRIORITY_RESIZE (+10) and GTK_PRIORITY_REDRAW (+20) */
-#define META_PRIORITY_RESIZE    (G_PRIORITY_HIGH_IDLE + 15)
-
 typedef struct _MetaUI MetaUI;
 
 typedef struct _MetaImageWindow MetaImageWindow;