Do not restart all thumbnailers on new entries

This had the potential to create tons of unnecessary processes
doing the same job.

The change only covers moving or linking, not copying.

fiv-browser.c

@@ -92,7 +92,8 @@ struct _FivBrowser {
 
 	Thumbnailer *thumbnailers;          ///< Parallelized thumbnailers
 	size_t thumbnailers_len;            ///< Thumbnailers array size
-	GQueue thumbnailers_queue;          ///< Queued up Entry pointers
+	GQueue thumbnailers_queue_1;        ///< Queued up Entry pointers, hi-prio
+	GQueue thumbnailers_queue_2;        ///< Queued up Entry pointers, lo-prio
 
 	GdkCursor *pointer;                 ///< Cached pointer cursor
 	cairo_pattern_t *glow;              ///< CAIRO_FORMAT_A8 mask for corners
@@ -742,7 +743,7 @@ thumbnailer_reprocess_entry(FivBrowser *self, GBytes *output, Entry *entry)
 	if ((flags & FIV_IO_SERIALIZE_LOW_QUALITY)) {
 		cairo_surface_set_user_data(entry->thumbnail, &fiv_thumbnail_key_lq,
 			(void *) (intptr_t) 1, NULL);
-		g_queue_push_tail(&self->thumbnailers_queue, entry);
+		g_queue_push_tail(&self->thumbnailers_queue_2, entry);
 	}
 
 	entry_set_surface_user_data(entry);
@@ -796,13 +797,21 @@ on_thumbnailer_ready(GObject *object, GAsyncResult *res, gpointer user_data)
 	thumbnailer_next(t);
 }
 
+// TODO(p): Try to keep the minions alive (stdout will be a problem).
 static gboolean
 thumbnailer_next(Thumbnailer *t)
 {
-	// TODO(p): Try to keep the minions alive (stdout will be a problem).
+	// Already have something to do, not a failure.
+	if (t->target)
+		return TRUE;
+
+	// They could have been removed via post-reload changes in the model.
 	FivBrowser *self = t->self;
-	if (!(t->target = g_queue_pop_head(&self->thumbnailers_queue)))
-		return FALSE;
+	do {
+		if (!(t->target = g_queue_pop_head(&self->thumbnailers_queue_1)) &&
+			!(t->target = g_queue_pop_head(&self->thumbnailers_queue_2)))
+			return FALSE;
+	} while (t->target->removed);
 
 	// Case analysis:
 	//  - We haven't found any thumbnail for the entry at all
@@ -839,7 +848,8 @@ thumbnailer_next(Thumbnailer *t)
 static void
 thumbnailers_abort(FivBrowser *self)
 {
-	g_queue_clear(&self->thumbnailers_queue);
+	g_queue_clear(&self->thumbnailers_queue_1);
+	g_queue_clear(&self->thumbnailers_queue_2);
 
 	for (size_t i = 0; i < self->thumbnailers_len; i++) {
 		Thumbnailer *t = self->thumbnailers + i;
@@ -855,35 +865,35 @@ thumbnailers_abort(FivBrowser *self)
 }
 
 static void
-thumbnailers_start(FivBrowser *self)
+thumbnailers_enqueue(FivBrowser *self, Entry *entry)
 {
-	thumbnailers_abort(self);
-	if (!self->model)
-		return;
-
-	GQueue lq = G_QUEUE_INIT;
-	for (guint i = 0; i < self->entries->len; i++) {
-		Entry *entry = self->entries->pdata[i];
-		if (entry->removed)
-			continue;
-
+	if (!entry->removed) {
 		if (entry->icon)
-			g_queue_push_tail(&self->thumbnailers_queue, entry);
+			g_queue_push_tail(&self->thumbnailers_queue_1, entry);
 		else if (cairo_surface_get_user_data(
 			entry->thumbnail, &fiv_thumbnail_key_lq))
-			g_queue_push_tail(&lq, entry);
-	}
-	while (!g_queue_is_empty(&lq)) {
-		g_queue_push_tail_link(
-			&self->thumbnailers_queue, g_queue_pop_head_link(&lq));
+			g_queue_push_tail(&self->thumbnailers_queue_2, entry);
 	}
+}
 
+static void
+thumbnailers_deploy(FivBrowser *self)
+{
 	for (size_t i = 0; i < self->thumbnailers_len; i++) {
 		if (!thumbnailer_next(self->thumbnailers + i))
 			break;
 	}
 }
 
+static void
+thumbnailers_restart(FivBrowser *self)
+{
+	thumbnailers_abort(self);
+	for (guint i = 0; i < self->entries->len; i++)
+		thumbnailers_enqueue(self, self->entries->pdata[i]);
+	thumbnailers_deploy(self);
+}
+
 // --- Boilerplate -------------------------------------------------------------
 
 G_DEFINE_TYPE_EXTENDED(FivBrowser, fiv_browser, GTK_TYPE_WIDGET, 0,
@@ -1004,7 +1014,7 @@ set_item_size(FivBrowser *self, FivThumbnailSize size)
 
 		g_hash_table_remove_all(self->thumbnail_cache);
 		reload_thumbnails(self);
-		thumbnailers_start(self);
+		thumbnailers_restart(self);
 
 		g_object_notify_by_pspec(
 			G_OBJECT(self), browser_properties[PROP_THUMBNAIL_SIZE]);
@@ -1872,7 +1882,8 @@ fiv_browser_init(FivBrowser *self)
 		g_malloc0_n(self->thumbnailers_len, sizeof *self->thumbnailers);
 	for (size_t i = 0; i < self->thumbnailers_len; i++)
 		self->thumbnailers[i].self = self;
-	g_queue_init(&self->thumbnailers_queue);
+	g_queue_init(&self->thumbnailers_queue_1);
+	g_queue_init(&self->thumbnailers_queue_2);
 
 	set_item_size(self, FIV_THUMBNAIL_SIZE_NORMAL);
 	self->show_labels = FALSE;
@@ -1917,8 +1928,9 @@ on_model_reloaded(FivIoModel *model, FivBrowser *self)
 	fiv_browser_select(self, selected_uri);
 	g_free(selected_uri);
 
+	// Restarting thumbnailers is critical, because they keep Entry pointers.
 	reload_thumbnails(self);
-	thumbnailers_start(self);
+	thumbnailers_restart(self);
 }
 
 static void
@@ -1933,8 +1945,8 @@ on_model_changed(FivIoModel *model, FivIoModelEntry *old, FivIoModelEntry *new,
 		g_ptr_array_add(self->entries, entry);
 
 		reload_one_thumbnail(self, entry);
-		// TODO(p): Try to add to thumbnailer queue if already started.
-		thumbnailers_start(self);
+		thumbnailers_enqueue(self, entry);
+		thumbnailers_deploy(self);
 		return;
 	}
 
@@ -1960,8 +1972,9 @@ on_model_changed(FivIoModel *model, FivIoModelEntry *old, FivIoModelEntry *new,
 		// so that there's no jumping around. Or, a bit more properly,
 		// move the thumbnail cache entry to the new URI.
 		reload_one_thumbnail(self, found);
-		// TODO(p): Try to add to thumbnailer queue if already started.
-		thumbnailers_start(self);
+		// TODO(p): Rather cancel the entry in any running thumbnailer,
+		// remove it from queues, and _enqueue() + _deploy().
+		thumbnailers_restart(self);
 	} else {
 		found->removed = TRUE;
 		gtk_widget_queue_draw(GTK_WIDGET(self));