Let important notifications seep into full display queue

When the display queue had is full and a new notification would come
in, new notification wouldn't get shown until a currently displayed
notification would timeout.

Even if the notification would have been shown on top of the displayed
queue. So e.g. if the displayed queue would have been filled with
"normal" urgency notifications, an incoming "urgent" notification would
have been delayed.

To let those more important notifications through, the tail of displayed
and head of waiting are swapped on every update if necessary.

CHANGELOG.md

@@ -5,6 +5,8 @@
 ### Added
 
 - `fullscreen` rule to hide notifications when a fullscreen window is active
+- When new notifications arrive, but display is full, important notifications don't
+  have to wait for a timeout in a displayed notification (#541)
 
 ## 1.3.2 - 2018-05-06
 

src/queues.c

@@ -258,7 +258,7 @@ void queues_history_pop(void)
         n->redisplayed = true;
         n->start = 0;
         n->timeout = settings.sticky_history ? 0 : n->timeout;
-        g_queue_push_head(waiting, n);
+        g_queue_insert_sorted(waiting, n, notification_cmp_data, NULL);
 }
 
 /* see queues.h */
@@ -381,6 +381,40 @@ void queues_update(bool fullscreen)
 
                 iter = nextiter;
         }
+
+        /* If displayed is actually full, let the more important notifications
+         * from waiting seep into displayed.
+         */
+        if (settings.sort) {
+                GList *i_waiting, *i_displayed;
+
+                while (   (i_waiting   = g_queue_peek_head_link(waiting))
+                       && (i_displayed = g_queue_peek_tail_link(displayed))) {
+
+                        while (   fullscreen
+                               && i_waiting
+                               && i_waiting->data
+                               && ((notification*) i_waiting->data)->fullscreen != FS_SHOW) {
+                                i_waiting = i_waiting->prev;
+                        }
+
+                        if (i_waiting && notification_cmp(i_displayed->data, i_waiting->data) > 0) {
+                                notification *towait = i_displayed->data;
+                                notification *todisp = i_waiting->data;
+
+                                g_queue_delete_link(displayed, i_displayed);
+                                g_queue_delete_link(waiting,   i_waiting);
+
+                                todisp->start = time_monotonic_now();
+                                notification_run_script(todisp);
+
+                                g_queue_insert_sorted(displayed, todisp, notification_cmp_data, NULL);
+                                g_queue_insert_sorted(waiting, towait, notification_cmp_data, NULL);
+                        } else {
+                                break;
+                        }
+                }
+        }
 }
 
 /* see queues.h */