timeline: Cancel additions and removals

When we add an event to the queue, and later remove it, if the
event is still in the queue, we can just cancel both out and
save the timeline some processing time.

src/core/gcal-timeline.c

@@ -77,6 +77,7 @@ struct _GcalTimeline
 
   GCancellable       *cancellable;
 
+  GHashTable         *queued_adds;
   GQueue             *event_queue;
   GSource            *timeline_source;
 
@@ -101,6 +102,13 @@ static GParamSpec *properties [N_PROPS] = { NULL, };
  * Auxiliary methods
  */
 
+static gchar*
+format_subscriber_event_id (GcalTimelineSubscriber *subscriber,
+                            GcalEvent              *event)
+{
+  return g_strdup_printf ("%s:%s", G_OBJECT_TYPE_NAME (subscriber), gcal_event_get_uid (event));
+}
+
 static void
 queue_data_free (QueueData *queue_data)
 {
@@ -118,6 +126,7 @@ queue_event_data (GcalTimeline           *self,
                   GcalEvent              *old_event,
                   gboolean                update_range_tree)
 {
+  g_autofree gchar *subscriber_event_id = NULL;
   QueueData *queue_data;
 
   queue_data = g_new0 (QueueData, 1);
@@ -128,7 +137,49 @@ queue_event_data (GcalTimeline           *self,
   queue_data->old_event = old_event ? g_object_ref (old_event) : NULL;
   queue_data->update_range_tree = update_range_tree;
 
+  subscriber_event_id = format_subscriber_event_id (subscriber, event);
+
+  switch (queue_event)
+    {
+    case ADD_EVENT:
+    case UPDATE_EVENT:
+      break;
+    case REMOVE_EVENT:
+        {
+          GList *queued_add_link;
+
+          queued_add_link = g_hash_table_lookup (self->queued_adds, subscriber_event_id);
+          if (queued_add_link)
+            {
+              QueueData *queued_add = queued_add_link->data;
+
+              GCAL_TRACE_MSG ("Removing ADD_EVENT for event '%s' (%s) from event queue",
+                              gcal_event_get_summary (event),
+                              subscriber_event_id);
+
+              g_hash_table_remove (self->queued_adds, subscriber_event_id);
+              g_queue_delete_link (self->event_queue, queued_add_link);
+              queue_data_free (queued_add);
+              return;
+            }
+        }
+      break;
+    }
+
   g_queue_push_tail (self->event_queue, queue_data);
+
+  switch (queue_event)
+    {
+    case ADD_EVENT:
+      g_hash_table_insert (self->queued_adds,
+                           g_steal_pointer (&subscriber_event_id),
+                           g_queue_peek_tail_link (self->event_queue));
+      break;
+
+    case UPDATE_EVENT:
+    case REMOVE_EVENT:
+      break;
+    }
 }
 
 static inline gboolean
@@ -608,6 +659,7 @@ timeline_source_dispatch (GSource     *source,
   while (processed_events < BATCH_SIZE && !g_queue_is_empty (self->event_queue))
     {
       GcalTimelineSubscriber *subscriber;
+      g_autofree gchar *subscriber_event_id = NULL;
       GcalRange *event_range;
       QueueData *queue_data;
       GcalEvent *event;
@@ -617,10 +669,12 @@ timeline_source_dispatch (GSource     *source,
       event = queue_data->event;
       subscriber = queue_data->subscriber;
       event_range = gcal_event_get_range (event);
+      subscriber_event_id = format_subscriber_event_id (subscriber, event);
 
       /* The subscriber may have been removed already */
       if (!g_hash_table_contains (self->subscribers, subscriber))
         {
+          g_hash_table_remove (self->queued_adds, subscriber_event_id);
           queue_data_free (queue_data);
           continue;
         }
@@ -628,10 +682,12 @@ timeline_source_dispatch (GSource     *source,
       switch (queue_data->queue_event)
         {
         case ADD_EVENT:
-          GCAL_TRACE_MSG ("Processing ADD_EVENT for event '%s' (%s)",
+          GCAL_TRACE_MSG ("Processing ADD_EVENT for event '%s' (%s) (in queued_adds: %d)",
                           gcal_event_get_summary (event),
-                          gcal_event_get_uid (event));
+                          gcal_event_get_uid (event),
+                          g_hash_table_contains (self->queued_adds, subscriber_event_id));
 
+          g_hash_table_remove (self->queued_adds, subscriber_event_id);
           if (queue_data->update_range_tree)
             gcal_range_tree_add_range (self->events, event_range, g_object_ref (event));
 
@@ -708,6 +764,7 @@ gcal_timeline_finalize (GObject *object)
   g_clear_pointer (&self->events, gcal_range_tree_unref);
   g_clear_pointer (&self->calendars, g_hash_table_destroy);
   g_clear_pointer (&self->subscribers, g_hash_table_destroy);
+  g_clear_pointer (&self->queued_adds, g_hash_table_destroy);
   g_clear_pointer (&self->subscriber_ranges, gcal_range_tree_unref);
 
   g_source_destroy (self->timeline_source);
@@ -829,6 +886,7 @@ gcal_timeline_init (GcalTimeline *self)
   self->subscribers = g_hash_table_new_full (NULL, NULL, g_object_unref, (GDestroyNotify) gcal_range_unref);
   self->subscriber_ranges = gcal_range_tree_new ();
   self->event_queue = g_queue_new ();
+  self->queued_adds = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, NULL);
 
   /* Timeline source */
   timeline_source = (TimelineSource*) g_source_new (&timeline_source_funcs, sizeof (TimelineSource));