[glib] g_cancellable_source_new: don't use a file descriptor

[Dan Winship <danw src gnome org>]

commit 09c18537f4e8b3ede066339cc23b76df8a4fc2cc
Author: Dan Winship <danw gnome org>
Date:   Tue Jul 17 13:17:01 2012 -0400

    g_cancellable_source_new: don't use a file descriptor
    
    Rather than implementing GCancellableSource by polling on its fd,
    implement it by just waking its GMainContext up from the "cancelled"
    signal handler, thereby helping to reduce file descriptor usage.
    Suggested by Ryan Lortie.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=680121

 gio/gcancellable.c |   24 +++++++++++++++++++-----
 1 files changed, 19 insertions(+), 5 deletions(-)
---
diff --git a/gio/gcancellable.c b/gio/gcancellable.c
index 8fb1195..0ba3a01 100644
--- a/gio/gcancellable.c
+++ b/gio/gcancellable.c
@@ -632,9 +632,17 @@ typedef struct {
   GSource       source;
 
   GCancellable *cancellable;
-  GPollFD       pollfd;
 } GCancellableSource;
 
+static void
+cancellable_source_cancelled (GCancellable *cancellable,
+			      gpointer      user_data)
+{
+  GSource *source = user_data;
+
+  g_main_context_wakeup (g_source_get_context (source));
+}
+
 static gboolean
 cancellable_source_prepare (GSource *source,
 			    gint    *timeout)
@@ -670,7 +678,12 @@ cancellable_source_finalize (GSource *source)
   GCancellableSource *cancellable_source = (GCancellableSource *)source;
 
   if (cancellable_source->cancellable)
-    g_object_unref (cancellable_source->cancellable);
+    {
+      g_signal_handlers_disconnect_by_func (cancellable_source->cancellable,
+					    G_CALLBACK (cancellable_source_cancelled),
+					    cancellable_source);
+      g_object_unref (cancellable_source->cancellable);
+    }
 }
 
 static gboolean
@@ -733,11 +746,12 @@ g_cancellable_source_new (GCancellable *cancellable)
   g_source_set_name (source, "GCancellable");
   cancellable_source = (GCancellableSource *)source;
 
-  if (g_cancellable_make_pollfd (cancellable,
-                                 &cancellable_source->pollfd))
+  if (cancellable)
     {
       cancellable_source->cancellable = g_object_ref (cancellable);
-      g_source_add_poll (source, &cancellable_source->pollfd);
+      g_signal_connect (cancellable, "cancelled",
+			G_CALLBACK (cancellable_source_cancelled),
+			source);
     }
 
   return source;