idle: added "update" event

Some clients have visual feedback for "database update is running".
Using the "database" idle event is unreliable, because it is only
emitted when the database was actually modified.  This patch adds the
"update" event, which is emitted when the update is started, and again
when the update is finished, disregarding whether it has been
modified.

NEWS

@@ -1,6 +1,7 @@
 ver 0.16 (20??/??/??)
 * protocol:
   - send song modification time to client
+  - added "update" idle event
 * decoders:
   - ffmpeg: support multiple tags
 * mixers:

doc/protocol.xml

@@ -134,7 +134,16 @@
               <listitem>
                 <para>
                   <returnvalue>database</returnvalue>: the song database
-                  has been updated
+                  has been modified
+                </para>
+              </listitem>
+              <listitem>
+                <para>
+                  <returnvalue>update</returnvalue>: a database update
+                  has started or finished.  If the database was
+                  modified during the update, the
+                  <returnvalue>database</returnvalue> event is also
+                  emitted.
                 </para>
               </listitem>
               <listitem>

src/idle.c

@@ -40,6 +40,7 @@ static const char *const idle_names[] = {
 	"output",
 	"options",
 	"sticker",
+	"update",
         NULL
 };
 

src/idle.h

@@ -50,6 +50,9 @@ enum {
 
 	/** a sticker has been modified. */
 	IDLE_STICKER = 0x80,
+
+	/** a database update has started or finished. */
+	IDLE_UPDATE = 0x100,
 };
 
 /**

src/update.c

@@ -822,6 +822,9 @@ directory_update_init(char *path)
 		return next_task_id > update_task_id_max ?  1 : next_task_id;
 	}
 	spawn_update_task(path);
+
+	idle_add(IDLE_UPDATE);
+
 	return update_task_id;
 }
 
@@ -861,6 +864,8 @@ static void update_finished_event(void)
 
 	g_thread_join(update_thr);
 
+	idle_add(IDLE_UPDATE);
+
 	if (modified) {
 		/* send "idle" events */
 		playlistVersionChange(&g_playlist);