see full message -- safe signal/lifetime/glib code

this unusually dense commit is the product of me using hostnamed as a
prototyping bed, you should instead follow the next numbered series of
commits to proceed this one, as they are the same changes but made
incrementally and gradually across the other three interfaces.

added:
 * proper lifetime handling, everything coordinated in a gmainloop such that
   daemons don't clean their memory twice or trip over the last instance's unclosed
   file descriptors, etc.

 * threadsafe unix termination signal handling

 * more intuitive runtime, daemons immidietly either start up perfectly and print
   a verification or crash and print a reason/probable solution

 * some bugfixes detailed in further individual commits

2 files changed, 78 insertions, 33 deletions

diff --git a/src/interfaces/hostnamed/hostnamed.c b/src/interfaces/hostnamed/hostnamed.c
index 9648d25..979df6e 100644
--- a/src/interfaces/hostnamed/hostnamed.c
+++ b/src/interfaces/hostnamed/hostnamed.c
@@ -16,6 +16,7 @@
 
 #include <unistd.h>
 #include <limits.h>
+#include <signal.h>
 
 #include <sys/param.h>
 #include <string.h>
@@ -24,10 +25,16 @@
 #include <glib-unix.h>
 
 #include "hostnamed-gen.h"
+#include "hostnamed.h"
 
 GPtrArray *hostnamed_freeable;
 Hostname1 *hostnamed_interf;
 
+GMainLoop *hostnamed_loop;
+
+guint bus_descriptor;
+gboolean dbus_interface_exported; /* reliable because of gdbus operational guarantees */
+
 /* --- begin method/property/dbus signal code --- */
 
 static gboolean
@@ -82,7 +89,7 @@ our_get_hostname() {
 	gchar *hostname_buf, *ret;
 	size_t hostname_divider;
 
-	hostname_buf = (gchar*) g_malloc0(MAXHOSTNAMELEN);
+	hostname_buf = (gchar*) g_malloc0(MAXHOSTNAMELEN); /* todo check & free */
 	ret          = (gchar*) g_malloc0(MAXHOSTNAMELEN);
 	g_ptr_array_add(hostnamed_freeable, hostname_buf);
 	g_ptr_array_add(hostnamed_freeable, ret);
@@ -155,17 +162,9 @@ static void hostnamed_on_bus_acquired(GDBusConnection *conn,
                             const gchar *name,
                             gpointer user_data) {
 
-    g_print("got bus, name: %s\n", name);   
+    g_printf("got bus/name, exporting %s's interface...\n", name);
 
-}
-
-static void hostnamed_on_name_acquired(GDBusConnection *conn,
-    		                           const gchar *name,
-                                       gpointer user_data) {
-
-    g_print("got '%s' on system bus\n", name);
-
-    hostnamed_interf = hostname1_skeleton_new();
+	hostnamed_interf = hostname1_skeleton_new();
 
     /* attach function pointers to generated struct's method handlers */
     g_signal_connect(hostnamed_interf, "handle-set-hostname", G_CALLBACK(on_handle_set_hostname), NULL);
@@ -191,54 +190,99 @@ static void hostnamed_on_name_acquired(GDBusConnection *conn,
                                          "/org/freedesktop/hostname1",
                                          NULL)) {
 
-        g_printf("Failed to export Hostname1's interface!");
-    }
+        g_printf("failed to export %s's interface!\n", name); /* unusual edge case, TODO check errno */
+		hostnamed_mem_clean();
 
-}
+    } else {
 
-/* --- end bus/name handlers, begin misc unix functions --- */
+		dbus_interface_exported = TRUE;
+		g_printf("exported %s's interface on the system bus...", name);
+	}
 
-/* free()'s */
-void hostnamed_mem_clean() {
+}
 
-    g_ptr_array_foreach(hostnamed_freeable, (GFunc) g_free, NULL);
-	g_ptr_array_free(hostnamed_freeable, TRUE);
+static void hostnamed_on_name_acquired(GDBusConnection *conn,
+    		                           const gchar *name,
+                                       gpointer user_data) {
+
+    g_printf("success!\n");
+ 
 }
 
 static void hostnamed_on_name_lost(GDBusConnection *conn,
                                    const gchar *name,
                                    gpointer user_data) {
 
-    g_print("lost name %s, exiting...", name);
+	if(!conn) {
+
+		g_printf("failed to connect to the system bus while trying to acquire name '%s': either dbus-daemon isn't running or we don't have permission to push names and/or their interfaces to it", name);
+
+		hostnamed_mem_clean();
+	}
+
+    g_printf("lost name %s, exiting...", name);
 
     hostnamed_mem_clean();
-    g_dbus_interface_skeleton_unexport(G_DBUS_INTERFACE_SKELETON(hostnamed_interf));
+}
+
+/* --- end bus/name handlers, begin misc unix functions --- */
+
+/* safe call to clean and then exit
+ * this stops our GMainLoop safely before letting main() return  */
+void hostnamed_mem_clean() {
+
+	g_printf("exiting...\n");
+
+	if(dbus_interface_exported)
+		g_dbus_interface_skeleton_unexport(G_DBUS_INTERFACE_SKELETON(hostnamed_interf));
+
+	if(g_main_loop_is_running(hostnamed_loop)) 
+		g_main_loop_quit(hostnamed_loop);
 
 }
 
-int main() {
+/* wrapper for glib's unix signal handling; called only once if terminatating signal is raised against us */
+gboolean unix_sig_terminate_handler(gpointer data) {
 
-	guint bus_descriptor;
-	GMainLoop *hostnamed_loop;
+	g_printf("caught SIGINT/HUP/TERM, exiting\n");
+
+	hostnamed_mem_clean();
+	return G_SOURCE_REMOVE; 
+}
+
+void set_signal_handlers() {
+
+	/* we don't care about its descriptor, we never need to unregister these */
+	g_unix_signal_add(SIGINT,  unix_sig_terminate_handler, NULL);
+	g_unix_signal_add(SIGHUP,  unix_sig_terminate_handler, NULL);
+	g_unix_signal_add(SIGTERM, unix_sig_terminate_handler, NULL);
+}
+
+int main() {
+	
+	set_signal_handlers();
 
 	hostnamed_loop = g_main_loop_new(NULL, TRUE);
 	hostnamed_freeable = g_ptr_array_new();
 
-	 bus_descriptor = g_bus_own_name(G_BUS_TYPE_SYSTEM,
-                                    "org.freedesktop.hostname1",
-                                    G_BUS_NAME_OWNER_FLAGS_NONE,
-                                    hostnamed_on_bus_acquired,
-                                    hostnamed_on_name_acquired,
-                                    hostnamed_on_name_lost,
-                                    NULL,
-                                    NULL);
+	bus_descriptor = g_bus_own_name(G_BUS_TYPE_SYSTEM,
+                                   "org.freedesktop.hostname1",
+                                   G_BUS_NAME_OWNER_FLAGS_NONE,
+                                   hostnamed_on_bus_acquired,
+                                   hostnamed_on_name_acquired,
+                                   hostnamed_on_name_lost,
+                                   NULL,
+                                   NULL);
 
 	g_main_loop_run(hostnamed_loop);
+	/* runs until single g_main_loop_quit() call is raised inside <interface>_mem_clean() */
 	g_main_loop_unref(hostnamed_loop);
 
+	/* guaranteed unownable */
 	g_bus_unown_name(bus_descriptor);
 
-	hostnamed_mem_clean();
+	/* at this point no operations can occur with our data, it is safe to free it + its container */
+	g_ptr_array_free(hostnamed_freeable, TRUE);
 
 	return 0;
 }
diff --git a/src/interfaces/hostnamed/hostnamed.h b/src/interfaces/hostnamed/hostnamed.h
new file mode 100644
index 0000000..e8c4e3a
--- /dev/null
+++ b/src/interfaces/hostnamed/hostnamed.h
@@ -0,0 +1 @@
+void hostnamed_mem_clean();