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gobject: Use compare and exchange full to re-read old ref value

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In case g_atomic_int_compare_and_exchange() check fails we ended up doing
another atomic get to figure out what it was the old reference count,
however, we can avoid this by using the full version of the function that
returns the value before the exchange happened as an out value.
This commit is contained in:
Marco Trevisan (Treviño) 2022-11-29 20:53:06 +01:00
parent 5f945e5464
commit c95bf0514c
1 changed files with 8 additions and 4 deletions
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12
gobject/gobject.c
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@ -3789,14 +3789,16 @@ g_object_unref (gpointer _object)
g_return_if_fail (G_IS_OBJECT (object));
/* here we want to atomically do: if (ref_count>1) { ref_count--; return; } */
retry_atomic_decrement1:
old_ref = g_atomic_int_get (&object->ref_count);
retry_atomic_decrement1:
if (old_ref > 1)
{
/* valid if last 2 refs are owned by this call to unref and the toggle_ref */
gboolean has_toggle_ref = OBJECT_HAS_TOGGLE_REF (object);
if (!g_atomic_int_compare_and_exchange ((int *)&object->ref_count, old_ref, old_ref - 1))
if (!g_atomic_int_compare_and_exchange_full ((int *)&object->ref_count,
old_ref, old_ref - 1,
&old_ref))
goto retry_atomic_decrement1;
TRACE (GOBJECT_OBJECT_UNREF(object,G_TYPE_FROM_INSTANCE(object),old_ref));
@ -3868,14 +3870,16 @@ g_object_unref (gpointer _object)
TRACE (GOBJECT_OBJECT_DISPOSE_END(object,G_TYPE_FROM_INSTANCE(object), 1));
/* may have been re-referenced meanwhile */
retry_atomic_decrement2:
old_ref = g_atomic_int_get ((int *)&object->ref_count);
retry_atomic_decrement2:
if (old_ref > 1)
{
/* valid if last 2 refs are owned by this call to unref and the toggle_ref */
gboolean has_toggle_ref = OBJECT_HAS_TOGGLE_REF (object);
if (!g_atomic_int_compare_and_exchange ((int *)&object->ref_count, old_ref, old_ref - 1))
if (!g_atomic_int_compare_and_exchange_full ((int *)&object->ref_count,
old_ref, old_ref - 1,
&old_ref))
goto retry_atomic_decrement2;
/* emit all notifications that have been queued during dispose() */