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gobject: fix race and use g_datalist_id_update_atomic() for closure array

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There are two calls to

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

that don't take a OPTIONAL_BIT_LOCK_CLOSURE_ARRAY lock.

One is right before finalize(), at which point it's most likely safe, as
nobody else should have a reference to the object to do anything
concurrently.

The other one is in g_object_real_dispose(). Usually, at this point too
no other thread has have a reference to the object. However, it could
obtain one by dispose() passing on a reference. In that case, the
removal of the quark_closure_array data can race against
g_object_watch_closure() and object_remove_closure().

Fix that, by having all operations on the CArray performed under a lock.
In this case, using the GData lock via g_datalist_id_update_atomic().

This also saves the additional OPTIONAL_BIT_LOCK_CLOSURE_ARRAY lock.
At the expense of doing slightly more work while holding the GData lock.

Also free the empty closure data during object_remove_closure(). This
frees some unused memory.
This commit is contained in:
Thomas Haller 2024-01-29 15:41:40 +01:00
parent 81fbff124e
commit 050315ac49
1 changed files with 78 additions and 45 deletions
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119
gobject/gobject.c
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@ -126,7 +126,6 @@ enum {
* (per-object!) is not worth it. */
#define OPTIONAL_BIT_LOCK_WEAK_REFS 1
#define OPTIONAL_BIT_LOCK_TOGGLE_REFS 2
#define OPTIONAL_BIT_LOCK_CLOSURE_ARRAY 3
#if SIZEOF_INT == 4 && GLIB_SIZEOF_VOID_P >= 8
#define HAVE_OPTIONAL_FLAGS_IN_GOBJECT 1
@ -5263,27 +5262,44 @@ typedef struct {
GClosure *closures[1]; /* flexible array */
} CArray;
static void
object_remove_closure (gpointer data,
GClosure *closure)
static gpointer
object_remove_closure_cb (gpointer *data,
GDestroyNotify *destroy_notify,
gpointer user_data)
{
GObject *object = data;
CArray *carray;
GClosure *closure = user_data;
CArray *carray = *data;
guint i;
object_bit_lock (object, OPTIONAL_BIT_LOCK_CLOSURE_ARRAY);
carray = g_object_get_qdata (object, quark_closure_array);
for (i = 0; i < carray->n_closures; i++)
if (carray->closures[i] == closure)
{
carray->n_closures--;
if (i < carray->n_closures)
carray->closures[i] = carray->closures[carray->n_closures];
object_bit_unlock (object, OPTIONAL_BIT_LOCK_CLOSURE_ARRAY);
return;
}
object_bit_unlock (object, OPTIONAL_BIT_LOCK_CLOSURE_ARRAY);
g_assert_not_reached ();
{
if (carray->closures[i] == closure)
{
carray->n_closures--;
if (carray->n_closures == 0)
{
g_free (carray);
*data = NULL;
}
else if (i < carray->n_closures)
carray->closures[i] = carray->closures[carray->n_closures];
return NULL;
}
}
g_return_val_if_reached (NULL);
}
static void
object_remove_closure (gpointer data,
GClosure *closure)
{
GObject *object = data;
_g_datalist_id_update_atomic (&object->qdata,
quark_closure_array,
object_remove_closure_cb,
closure);
}
static void
@ -5306,6 +5322,38 @@ destroy_closure_array (gpointer data)
g_free (carray);
}
static gpointer
g_object_watch_closure_cb (gpointer *data,
GDestroyNotify *destroy_notify,
gpointer user_data)
{
GObject *object = ((gpointer *) user_data)[0];
GClosure *closure = ((gpointer *) user_data)[1];
CArray *carray = *data;
guint i;
if (!carray)
{
carray = g_new (CArray, 1);
carray->object = object;
carray->n_closures = 1;
i = 0;
*destroy_notify = destroy_closure_array;
}
else
{
i = carray->n_closures++;
carray = g_realloc (carray, sizeof (*carray) + sizeof (carray->closures[0]) * i);
}
*data = carray;
carray->closures[i] = closure;
return NULL;
}
/**
* g_object_watch_closure:
* @object: #GObject restricting lifetime of @closure
@ -5322,39 +5370,24 @@ destroy_closure_array (gpointer data)
* use this @object as closure data.
*/
void
g_object_watch_closure (GObject *object,
GClosure *closure)
g_object_watch_closure (GObject *object,
GClosure *closure)
{
CArray *carray;
guint i;
g_return_if_fail (G_IS_OBJECT (object));
g_return_if_fail (closure != NULL);
g_return_if_fail (closure->is_invalid == FALSE);
g_return_if_fail (closure->in_marshal == FALSE);
g_return_if_fail (g_atomic_int_get (&object->ref_count) > 0); /* this doesn't work on finalizing objects */
g_return_if_fail (g_atomic_int_get (&object->ref_count) > 0); /* this doesn't work on finalizing objects */
g_closure_add_invalidate_notifier (closure, object, object_remove_closure);
g_closure_add_marshal_guards (closure,
object, (GClosureNotify) g_object_ref,
object, (GClosureNotify) g_object_unref);
object_bit_lock (object, OPTIONAL_BIT_LOCK_CLOSURE_ARRAY);
carray = g_datalist_id_remove_no_notify (&object->qdata, quark_closure_array);
if (!carray)
{
carray = g_renew (CArray, NULL, 1);
carray->object = object;
carray->n_closures = 1;
i = 0;
}
else
{
i = carray->n_closures++;
carray = g_realloc (carray, sizeof (*carray) + sizeof (carray->closures[0]) * i);
}
carray->closures[i] = closure;
g_datalist_id_set_data_full (&object->qdata, quark_closure_array, carray, destroy_closure_array);
object_bit_unlock (object, OPTIONAL_BIT_LOCK_CLOSURE_ARRAY);
object, (GClosureNotify) g_object_ref,
object, (GClosureNotify) g_object_unref);
_g_datalist_id_update_atomic (&object->qdata,
quark_closure_array,
g_object_watch_closure_cb,
((gpointer[]){ object, closure }));
}
/**