[gnome-photos] tracker-queue: Make the GInitable implementation idempotent

[Debarshi Ray <debarshir src gnome org>]

commit 51b2290601494d4aa900d838179ab63012ffd214
Author: Debarshi Ray <debarshir gnome org>
Date:   Fri Jun 30 20:37:26 2017 +0200

    tracker-queue: Make the GInitable implementation idempotent
    
    The earlier implementation would violate idempotency if the first
    attempt to get a TrackerSparqlConnection failed but a subsequent one
    succeeded. Idempotency is important because it is a singleton class.

 src/photos-tracker-queue.c |   37 ++++++++++++++++++++++++++++++++-----
 1 files changed, 32 insertions(+), 5 deletions(-)
---
diff --git a/src/photos-tracker-queue.c b/src/photos-tracker-queue.c
index 26fdc1c..38feffd 100644
--- a/src/photos-tracker-queue.c
+++ b/src/photos-tracker-queue.c
@@ -35,8 +35,10 @@
 struct _PhotosTrackerQueue
 {
   GObject parent_instance;
+  GError *initialization_error;
   GQueue *queue;
   TrackerSparqlConnection *connection;
+  gboolean is_initialized;
   gboolean running;
 };
 
@@ -67,6 +69,9 @@ struct _PhotosTrackerQueueData
 };
 
 
+G_LOCK_DEFINE_STATIC (init_lock);
+
+
 static void photos_tracker_queue_check (PhotosTrackerQueue *self);
 
 
@@ -207,6 +212,7 @@ photos_tracker_queue_finalize (GObject *object)
 {
   PhotosTrackerQueue *self = PHOTOS_TRACKER_QUEUE (object);
 
+  g_clear_error (&self->initialization_error);
   g_queue_free (self->queue);
 
   G_OBJECT_CLASS (photos_tracker_queue_parent_class)->finalize (object);
@@ -235,16 +241,37 @@ static gboolean
 photos_tracker_queue_initable_init (GInitable *initable, GCancellable *cancellable, GError **error)
 {
   PhotosTrackerQueue *self = PHOTOS_TRACKER_QUEUE (initable);
-  gboolean ret_val = TRUE;
+  gboolean ret_val = FALSE;
+
+  G_LOCK (init_lock);
 
-  if (G_LIKELY (self->connection != NULL))
+  if (self->is_initialized)
+    {
+      if (self->connection != NULL)
+        ret_val = TRUE;
+      else
+        g_assert_nonnull (self->initialization_error);
+
+      goto out;
+    }
+
+  g_assert_no_error (self->initialization_error);
+
+  self->connection = tracker_sparql_connection_get (cancellable, &self->initialization_error);
+  if (G_UNLIKELY (self->initialization_error != NULL))
     goto out;
 
-  self->connection = tracker_sparql_connection_get (cancellable, error);
-  if (G_UNLIKELY (self->connection == NULL))
-    ret_val = FALSE;
+  ret_val = TRUE;
 
  out:
+  self->is_initialized = TRUE;
+  if (!ret_val)
+    {
+      g_assert_nonnull (self->initialization_error);
+      g_propagate_error (error, g_error_copy (self->initialization_error));
+    }
+
+  G_UNLOCK (init_lock);
   return ret_val;
 }