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gobject: fix race and use g_datalist_id_update_atomic() for weak refs

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Note that we have two calls

  g_datalist_id_set_data (&object->qdata, quark_weak_notifies, NULL);

that don't take OPTIONAL_BIT_LOCK_WEAK_REFS lock. One is right before
finalize(). At that point, no other thread can hold a reference to the
object to race. One call is from g_object_real_dispose(). At this point,
theoretically the object could have been resurrected and a pointer
passed to another thread, so it can race against g_object_weak_ref()
and g_object_weak_unref().

Fix that, by performing all operations on the WeakRefStack while holding
the GData lock. By using g_datalist_id_update_atomic(), we no longer
need the OPTIONAL_BIT_LOCK_WEAK_REFS lock. On the other hand, we might
now do slightly more work while holding the GData lock.

Also, during g_object_weak_unref() free the WeakRefStack, if there
are no more references.
This commit is contained in:
Thomas Haller 2024-01-29 15:41:40 +01:00
parent 050315ac49
commit fbfccb70f8
1 changed files with 86 additions and 50 deletions
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122
gobject/gobject.c
View File

@ -124,8 +124,7 @@ enum {
* parallel as possible. The alternative would be to add individual locking
* integers to GObjectPrivate. But increasing memory usage for more parallelism
* (per-object!) is not worth it. */
#define OPTIONAL_BIT_LOCK_WEAK_REFS 1
#define OPTIONAL_BIT_LOCK_TOGGLE_REFS 2
#define OPTIONAL_BIT_LOCK_TOGGLE_REFS 1
#if SIZEOF_INT == 4 && GLIB_SIZEOF_VOID_P >= 8
#define HAVE_OPTIONAL_FLAGS_IN_GOBJECT 1
@ -3714,6 +3713,40 @@ weak_refs_notify (gpointer data)
g_free (wstack);
}
static gpointer
g_object_weak_ref_cb (gpointer *data,
GDestroyNotify *destroy_notify,
gpointer user_data)
{
GObject *object = ((gpointer *) user_data)[0];
GWeakNotify notify = ((gpointer *) user_data)[1];
gpointer notify_data = ((gpointer *) user_data)[2];
WeakRefStack *wstack = *data;
guint i;
if (!wstack)
{
wstack = g_new (WeakRefStack, 1);
wstack->object = object;
wstack->n_weak_refs = 1;
i = 0;
*destroy_notify = weak_refs_notify;
}
else
{
i = wstack->n_weak_refs++;
wstack = g_realloc (wstack, sizeof (*wstack) + sizeof (wstack->weak_refs[0]) * i);
}
*data = wstack;
wstack->weak_refs[i].notify = notify;
wstack->weak_refs[i].data = notify_data;
return NULL;
}
/**
* g_object_weak_ref: (skip)
* @object: #GObject to reference weakly
@ -3736,31 +3769,54 @@ g_object_weak_ref (GObject *object,
GWeakNotify notify,
gpointer data)
{
WeakRefStack *wstack;
guint i;
g_return_if_fail (G_IS_OBJECT (object));
g_return_if_fail (notify != NULL);
g_return_if_fail (g_atomic_int_get (&object->ref_count) >= 1);
object_bit_lock (object, OPTIONAL_BIT_LOCK_WEAK_REFS);
wstack = g_datalist_id_remove_no_notify (&object->qdata, quark_weak_notifies);
_g_datalist_id_update_atomic (&object->qdata,
quark_weak_notifies,
g_object_weak_ref_cb,
((gpointer[]){ object, notify, data }));
}
static gpointer
g_object_weak_unref_cb (gpointer *data,
GDestroyNotify *destroy_notify,
gpointer user_data)
{
GWeakNotify notify = ((gpointer *) user_data)[0];
gpointer notify_data = ((gpointer *) user_data)[1];
WeakRefStack *wstack = *data;
gboolean found_one = FALSE;
guint i;
if (wstack)
{
i = wstack->n_weak_refs++;
wstack = g_realloc (wstack, sizeof (*wstack) + sizeof (wstack->weak_refs[0]) * i);
}
else
for (i = 0; i < wstack->n_weak_refs; i++)
{
wstack = g_renew (WeakRefStack, NULL, 1);
wstack->object = object;
wstack->n_weak_refs = 1;
i = 0;
if (wstack->weak_refs[i].notify != notify ||
wstack->weak_refs[i].data != notify_data)
continue;
wstack->n_weak_refs -= 1;
if (wstack->n_weak_refs == 0)
{
g_free (wstack);
*data = NULL;
}
wstack->weak_refs[i].notify = notify;
wstack->weak_refs[i].data = data;
g_datalist_id_set_data_full (&object->qdata, quark_weak_notifies, wstack, weak_refs_notify);
object_bit_unlock (object, OPTIONAL_BIT_LOCK_WEAK_REFS);
else if (i != wstack->n_weak_refs)
wstack->weak_refs[i] = wstack->weak_refs[wstack->n_weak_refs];
found_one = TRUE;
break;
}
}
if (!found_one)
g_critical ("%s: couldn't find weak ref %p(%p)", G_STRFUNC, notify, notify_data);
return NULL;
}
/**
@ -3776,33 +3832,13 @@ g_object_weak_unref (GObject *object,
GWeakNotify notify,
gpointer data)
{
WeakRefStack *wstack;
gboolean found_one = FALSE;
g_return_if_fail (G_IS_OBJECT (object));
g_return_if_fail (notify != NULL);
object_bit_lock (object, OPTIONAL_BIT_LOCK_WEAK_REFS);
wstack = g_datalist_id_get_data (&object->qdata, quark_weak_notifies);
if (wstack)
{
guint i;
for (i = 0; i < wstack->n_weak_refs; i++)
if (wstack->weak_refs[i].notify == notify &&
wstack->weak_refs[i].data == data)
{
found_one = TRUE;
wstack->n_weak_refs -= 1;
if (i != wstack->n_weak_refs)
wstack->weak_refs[i] = wstack->weak_refs[wstack->n_weak_refs];
break;
}
}
object_bit_unlock (object, OPTIONAL_BIT_LOCK_WEAK_REFS);
if (!found_one)
g_critical ("%s: couldn't find weak ref %p(%p)", G_STRFUNC, notify, data);
_g_datalist_id_update_atomic (&object->qdata,
quark_weak_notifies,
g_object_weak_unref_cb,
((gpointer[]){ notify, data }));
}
/**