event_pipe: added pipe_event enum and callbacks

Make the event_pipe (formerly main_notify) send/receive a set of
events, with a callback for each one.

The default event PIPE_EVENT_SIGNAL does not have a callback.  It
is still there for waking up the main thread, when it is waiting for
the player thread.

src/main.c

@@ -190,17 +190,15 @@ timer_save_state_file(G_GNUC_UNUSED gpointer data)
 	return true;
 }
 
-void
-main_notify_triggered(void)
+/**
+ * event_pipe callback function for PIPE_EVENT_IDLE
+ */
+static void
+idle_event_emitted(void)
 {
-	unsigned flags;
-
-	syncPlayerAndPlaylist();
-	reap_update_task();
-
 	/* send "idle" notificaions to all subscribed
 	   clients */
-	flags = idle_get();
+	unsigned flags = idle_get();
 	if (flags != 0)
 		client_manager_idle_add(flags);
 }
@@ -243,6 +241,10 @@ int main(int argc, char *argv[])
 
 	main_loop = g_main_loop_new(NULL, FALSE);
 
+	event_pipe_init();
+	event_pipe_register(PIPE_EVENT_IDLE, idle_event_emitted);
+	event_pipe_register(PIPE_EVENT_PLAYLIST, syncPlayerAndPlaylist);
+
 	path_global_init();
 	mapper_init();
 	initPermissions();
@@ -253,8 +255,6 @@ int main(int argc, char *argv[])
 	decoder_plugin_init_all();
 	update_global_init();
 
-	event_pipe_init();
-
 	openDB(&options, argv[0]);
 
 	command_init();