From 09c18537f4e8b3ede066339cc23b76df8a4fc2cc Mon Sep 17 00:00:00 2001
From: Dan Winship <danw@gnome.org>
Date: Tue, 17 Jul 2012 13:17:01 -0400
Subject: [PATCH] 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 file 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;
-- 
2.7.4