Implement basic unique app behaviour via GApplication. (#8808)

Requires GIO 2.28, checks for it will be added later.

src/main.c

@@ -14,6 +14,7 @@
 
 #include <glib/gi18n.h>
 #include <gtk/gtk.h>
+#include <gio/gio.h>
 
 #include "settings.h"
 #include "process-window.h"
@@ -146,6 +147,8 @@ refresh_rate_changed (void)
 
 int main (int argc, char *argv[])
 {
+	GApplication *app;
+	GError *error = NULL;
 #ifdef ENABLE_NLS
 	bindtextdomain (GETTEXT_PACKAGE, PACKAGE_LOCALE_DIR);
 	bind_textdomain_codeset (GETTEXT_PACKAGE, "UTF-8");
@@ -155,6 +158,22 @@ int main (int argc, char *argv[])
 	gtk_init (&argc, &argv);
 	g_set_application_name (_("Task Manager"));
 
+	app = g_application_new ("xfce.taskmanager", 0);
+	g_application_register (G_APPLICATION (app), NULL, &error);
+	if (error != NULL)
+	{
+		g_warning ("Unable to register GApplication: %s", error->message);
+		g_error_free (error);
+		error = NULL;
+	}
+
+	if (g_application_get_is_remote (G_APPLICATION (app)))
+	{
+		g_application_activate (G_APPLICATION (app));
+		g_object_unref (app);
+		return 0;
+	}
+
 	settings = xtm_settings_get_default ();
 
 	status_icon = gtk_status_icon_new_from_icon_name ("utilities-system-monitor");
@@ -164,6 +183,7 @@ int main (int argc, char *argv[])
 
 	window = xtm_process_window_new ();
 	gtk_widget_show (window);
+	g_signal_connect_swapped (app, "activate", G_CALLBACK (xtm_process_window_show), window);
 
 	task_manager = xtm_task_manager_new (xtm_process_window_get_model (XTM_PROCESS_WINDOW (window)));
 	g_message ("Running as %s on %s", xtm_task_manager_get_username (task_manager), xtm_task_manager_get_hostname (task_manager));