g_timeout_add () callback funtion

DSP_LOAD.C
/* Declared in `server_switch.c`. */
extern GPid pid;

gboolean
dsp_load (gpointer data)
{
	float dsp;
	jack_client_t *client;
	jack_status_t *status;
	gchar print_dsp[6];
	//gboolean check;

	//check = gtk_switch_get_active (sw);
	client = jack_client_open ("default", JackNullOption, status);

	if (pid == 0)
	{
		return FALSE;
	}
	else
	{
		dsp = jack_cpu_load (client);
		sprintf (print_dsp, "%.2f", dsp);
		gtk_label_set_text (GTK_LABEL (label_dsp), print_dsp);

		return TRUE;
	}
}

SERVER_SWITCH.C
gchar driver_arg1[20];
gchar driver_arg2[20];

extern GtkWidget *box;

GPid pid;

/* `switch_pos` will start JACK when switched on and terminate it when switched off. */
void
switch_pos_new_cb (GtkSwitch *sw, gpointer data)
{
	gboolean check;
	gchar *jack_args[10];

	/* Declared with static or else `pid` will reset to 0 in the else command. */
	//static GPid pid;

	check = gtk_switch_get_active (sw);
	jack_args[0] = "jackd";
	jack_args[1] = rt_arg ();
	jack_args[2] = "-P75";
	jack_args[3] = driver_arg1;
	jack_args[4] = driver_arg2;
	jack_args[5] = NULL;

	if (check == TRUE)
	{
		gtk_widget_set_tooltip_text (GTK_WIDGET (sw) , "Shutdown Server");
		g_spawn_async (NULL, jack_args, NULL, G_SPAWN_SEARCH_PATH, NULL, NULL, &pid, NULL);

		g_timeout_add (2000, (GSourceFunc) dsp_load, (gpointer) sw); //<-- g_timeout_add () function call
	}
	else
	{
		gtk_widget_set_tooltip_text (GTK_WIDGET (sw) , "Start Server");
		kill (pid, SIGTERM);
	}
}

void
server_switch (GtkWidget *box_main)
{
	GtkWidget *jack_switch;
	GtkWidget *vbox;
	GtkWidget *label;
	gchar result[10];
	gboolean check;
	PangoAttrList *list;
	PangoAttribute *underline;
	FILE *cmd;

	cmd = popen ("pgrep jackd", "r");
	jack_switch = gtk_switch_new ();
	vbox = gtk_box_new (GTK_ORIENTATION_VERTICAL, 2);
	label = gtk_label_new ("JACK");
	check = gtk_switch_get_active (GTK_SWITCH (jack_switch));
	list = pango_attr_list_new ();
	underline = pango_attr_underline_new (PANGO_UNDERLINE_SINGLE);

	pango_attr_list_insert (list, underline);

	//gtk_label_set_attributes (GTK_LABEL (label), list);

	while (fgets (result, sizeof (result), cmd) != NULL)
	{
		g_print ("%s\n", result);
		pid = atoi (result);
		g_print ("%d\n", pid);
	}

	gtk_box_pack_start (GTK_BOX (vbox), label, FALSE, TRUE, 6);
	gtk_box_pack_start (GTK_BOX (vbox), jack_switch, FALSE, TRUE, 0);
	drivers (vbox);
	gtk_box_pack_start (GTK_BOX (box_main), vbox, FALSE, TRUE, 2);
	rt_box (box_main);



	/* Signal that works here for the `GtkSwitch` is `notify::active` which is a
		different convention used for other widget's signals that I've used. */
	if (pid != 0)
	{
		gtk_switch_set_active (GTK_SWITCH (jack_switch), TRUE);

		g_signal_connect (jack_switch, "notify::active", G_CALLBACK (switch_pos_new_cb), NULL);
	}
	else
	{
		g_signal_connect (jack_switch, "notify::active", G_CALLBACK (switch_pos_new_cb), NULL);
	}

	/* Initiate tooltip for `jack_switch` here or else it won't show when app first starts. */
	if (check == TRUE)
	{
		gtk_widget_set_tooltip_text (GTK_WIDGET (jack_switch) , "Shutdown Server");
	}
	else
	{
		gtk_widget_set_tooltip_text (GTK_WIDGET (jack_switch) , "Start Server");
	}
}