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

@@ -797,14 +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;
+	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
@@ -858,29 +865,35 @@ thumbnailers_abort(FivBrowser *self)
 }
 
 static void
-thumbnailers_restart(FivBrowser *self)
+thumbnailers_enqueue(FivBrowser *self, Entry *entry)
 {
-	thumbnailers_abort(self);
+	if (!entry->removed) {
-	if (!self->model)
-		return;
-
-	for (guint i = 0; i < self->entries->len; i++) {
-		Entry *entry = self->entries->pdata[i];
-		if (entry->removed)
-			continue;
-
 		if (entry->icon)
 			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(&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,
@@ -1915,6 +1928,7 @@ 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_restart(self);
 }
@@ -1931,10 +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): This is important!
+		thumbnailers_enqueue(self, entry);
-		// thumbnailers_restart() disowns existing processes.
+		thumbnailers_deploy(self);
-		// TODO(p): Try to add to thumbnailer queue if already started.
-		thumbnailers_restart(self);
 		return;
 	}
 
@@ -1960,7 +1972,8 @@ 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.
+		// TODO(p): Rather cancel the entry in any running thumbnailer,
+		// remove it from queues, and _enqueue() + _deploy().
 		thumbnailers_restart(self);
 	} else {
 		found->removed = TRUE;