Use weston_compositor_add_destroy_listener_once() in plugins

This introduces a new convention of checking through the compositor destroy
listener if the plugin is already initialized. If the plugin is already
initialized, then the plugin entry function succeeds as a no-op. This makes it
safe to load the same plugin multiple times in a running compositor.

Currently module loading functions return failure if a plugin is already
loaded, but that will change in the future. Therefore we need this other method
of ensuring we do not double-initialize a plugin which would lead to list
corruptions the very least.

All plugins are converted to use the new helper, except:
- those that do not have a destroy listener already, and
- hmi-controller which does the same open-coded as the common code pattern
  did not fit there.

Plugins should always have a compositor destroy listener registered since they
very least allocate a struct to hold their data. Hence omissions are
highlighted in code.

Backends do not need this because weston_compositor_load_backend() already
protects against double-init. GL-renderer does not export a standard module
init function so cannot be initialized the usual way and therefore is not
vulnerable to double-init.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

compositor/cms-colord.c

@@ -528,6 +528,14 @@ wet_module_init(struct weston_compositor *ec,
 	if (cms == NULL)
 		return -1;
 	cms->ec = ec;
+
+	if (!weston_compositor_add_destroy_listener_once(ec,
+							 &cms->destroy_listener,
+							 colord_notifier_destroy)) {
+		free(cms);
+		return 0;
+	}
+
 #if !GLIB_CHECK_VERSION(2,36,0)
 	g_type_init();
 #endif
@@ -543,10 +551,6 @@ wet_module_init(struct weston_compositor *ec,
 	cms->devices = g_hash_table_new_full(g_str_hash, g_str_equal,
 					     g_free, colord_cms_output_destroy);
 
-	/* destroy */
-	cms->destroy_listener.notify = colord_notifier_destroy;
-	wl_signal_add(&ec->destroy_signal, &cms->destroy_listener);
-
 	/* devices added */
 	cms->output_created_listener.notify = colord_notifier_output_created;
 	wl_signal_add(&ec->output_created_signal, &cms->output_created_listener);

compositor/cms-static.c

@@ -105,8 +105,13 @@ wet_module_init(struct weston_compositor *ec,
 		return -1;
 
 	cms->ec = ec;
-	cms->destroy_listener.notify = cms_notifier_destroy;
-	wl_signal_add(&ec->destroy_signal, &cms->destroy_listener);
+
+	if (!weston_compositor_add_destroy_listener_once(ec,
+							 &cms->destroy_listener,
+							 cms_notifier_destroy)) {
+		free(cms);
+		return 0;
+	}
 
 	cms->output_created_listener.notify = cms_notifier_output_created;
 	wl_signal_add(&ec->output_created_signal, &cms->output_created_listener);

compositor/screen-share.c

@@ -114,6 +114,9 @@ struct ss_shm_buffer {
 
 struct screen_share {
 	struct weston_compositor *compositor;
+	/* XXX: missing compositor destroy listener
+	 * https://gitlab.freedesktop.org/wayland/weston/issues/298
+	 */
 	char *command;
 };
 

compositor/systemd-notify.c

@@ -127,10 +127,12 @@ wet_module_init(struct weston_compositor *compositor,
 	if (notifier == NULL)
 		return -1;
 
-	notifier->compositor_destroy_listener.notify =
-		weston_compositor_destroy_listener;
-	wl_signal_add(&compositor->destroy_signal,
-		      &notifier->compositor_destroy_listener);
+	if (!weston_compositor_add_destroy_listener_once(compositor,
+							 &notifier->compositor_destroy_listener,
+							 weston_compositor_destroy_listener)) {
+		free(notifier);
+		return 0;
+	}
 
 	if (add_systemd_sockets(compositor) < 0)
 		return -1;