[rygel] server: Clarify signal emission

[Jens Georg <jensgeorg src gnome org>]

commit 3ea7296ed0ee53612c63158d1874068665ebe872
Author: Jens Georg <jensg openismus com>
Date:   Wed Mar 20 17:55:49 2013 +0100

    server: Clarify signal emission

 src/librygel-server/rygel-data-source.vala |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/src/librygel-server/rygel-data-source.vala b/src/librygel-server/rygel-data-source.vala
index 8eebcf6..437f550 100644
--- a/src/librygel-server/rygel-data-source.vala
+++ b/src/librygel-server/rygel-data-source.vala
@@ -93,16 +93,22 @@ public interface Rygel.DataSource : GLib.Object {
 
     /**
      * Emitted when the source has produced some data.
+     *
+     * This signal has to be emitted in the main thread.
      */
     public signal void data_available (uint8[] data);
 
     /**
      * Emitted when the source does not have data anymore.
+     *
+     * This signal has to be emitted in the main thread.
      */
     public signal void done ();
 
     /**
      * Emitted when the source encounters a problem during data generation.
+     *
+     * This signal has to be emitted in the main thread.
      */
     public signal void error (Error error);
 }