A while ago, I’ve described how to handle restarting Flatpak apps when they are updated.

While I showed working code back then, the example was a bit  contrived, since it had to work around GApplication’s built-in uniqueness features.

With the just-landed support for replacement in GApplication, this is now much more straightforward, and I’ve updated my example to show how it works.

Restart yourself

There are a few steps to this.

First, we need to opt into allowing replacement by passing G_APPLICATION_ALLOW_REPLACEMENT when creating our GApplication:

app = g_object_new (portal_test_app_get_type (),
        "application-id", "org.gnome.PortalTest",
        "flags", G_APPLICATION_ALLOW_REPLACEMENT,
        NULL);

This flag makes GApplication handle a –gapplication-replace commandline option, which we will see in action later.

Next, we monitor the /app/.updated file. Flatpak creates this file inside a running sandbox when a new version of the app is available, so this is our signal to restart ourselves:

file = g_file_new_for_path ("/app/.updated");
update_monitor =
       g_file_monitor_file (file, 0, NULL, NULL);
g_signal_connect (update_monitor, "changed",
       G_CALLBACK (update_monitor_changed), win);

The update_monitor_changed function presents a dialog that offers the user to restart the app:

 if (response == GTK_RESPONSE_OK)
      portal_test_app_restart (app);

The portal_test_app_restart function is where we take advantage of the new GApplication functionality:

const char *argv[3] = {
    "/app/bin/portal-test",
    "--gapplication-replace",
    NULL
};

xdp_flatpak_call_spawn (flatpak, cwd, argv, ...);

We call the Spawn method of the Flatpak portal, passing –gapplication-replace as an commandline option, and everything else is handled for us. Easy!

Update 1: If D-Bus is not your thing, there is a simple commandline tool called flatpak-spawn that can be used for the same purpose. It is available inside the sandbox.

Update 2: I forgot to mention that GApplication has also gained a name-lost signal. It can be used to save state in the old instance that can then be loaded in the new instance.