[glib] Fix race in g_cancellable_cancel()

[Ryan Lortie <ryanl src gnome org>]

commit e7763678b56e3be073cc55d707a6e92fc2055ee0
Author: Benjamin Otte <otte redhat com>
Date:   Fri Mar 26 20:37:09 2010 +0100

    Fix race in g_cancellable_cancel()
    
    We need to check priv->cancelled after taking the lock. Previously we
    only checked it just before taking the lock, which left a small chance
    for a race.

 gio/gcancellable.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/gio/gcancellable.c b/gio/gcancellable.c
index 2d600c9..32d01ae 100644
--- a/gio/gcancellable.c
+++ b/gio/gcancellable.c
@@ -622,6 +622,11 @@ g_cancellable_cancel (GCancellable *cancellable)
   priv = cancellable->priv;
 
   G_LOCK(cancellable);
+  if (priv->cancelled)
+    {
+      G_UNLOCK (cancellable);
+      return;
+    }
 
   priv->cancelled = TRUE;
   priv->cancelled_running = TRUE;