[glib] GVariant: add preconditions to ref. counting functions

[Philip Withnall <pwithnall src gnome org>]

commit 22da18fa706c685da015c9b9a786d810270b3a5f
Author: Philip Withnall <philip tecnocode co uk>
Date:   Wed Nov 30 10:20:13 2011 +0000

    GVariant: add preconditions to ref. counting functions
    
    These prevent GVariants from accidentally being brought back to life after
    being freed, and should make it easier to track down ref. counting issues.
    
    Closes: bgo#665184

 glib/gvariant-core.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)
---
diff --git a/glib/gvariant-core.c b/glib/gvariant-core.c
index 436d4bf..fdbe034 100644
--- a/glib/gvariant-core.c
+++ b/glib/gvariant-core.c
@@ -619,6 +619,9 @@ g_variant_is_trusted (GVariant *value)
 void
 g_variant_unref (GVariant *value)
 {
+  g_return_if_fail (value != NULL);
+  g_return_if_fail (value->ref_count > 0);
+
   if (g_atomic_int_dec_and_test (&value->ref_count))
     {
       if G_UNLIKELY (value->state & STATE_LOCKED)
@@ -652,6 +655,9 @@ g_variant_unref (GVariant *value)
 GVariant *
 g_variant_ref (GVariant *value)
 {
+  g_return_val_if_fail (value != NULL, NULL);
+  g_return_val_if_fail (value->ref_count > 0, NULL);
+
   g_atomic_int_inc (&value->ref_count);
 
   return value;
@@ -691,6 +697,9 @@ g_variant_ref (GVariant *value)
 GVariant *
 g_variant_ref_sink (GVariant *value)
 {
+  g_return_val_if_fail (value != NULL, NULL);
+  g_return_val_if_fail (value->ref_count > 0, NULL);
+
   g_variant_lock (value);
 
   if (~value->state & STATE_FLOATING)
@@ -746,6 +755,7 @@ GVariant *
 g_variant_take_ref (GVariant *value)
 {
   g_return_val_if_fail (value != NULL, NULL);
+  g_return_val_if_fail (value->ref_count > 0, NULL);
 
   g_atomic_int_and (&value->state, ~STATE_FLOATING);