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gobject: Cleanup GWeakRef locations on object finalization

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It can happen that a GWeakRef is added to an object while it's disposing
(or even during finalizing) and this may happen in a thread that (weak)
references an object while the disposal isn't completed yet or when
using toggle references and switching to GWeakRef on notification (as
the API suggests).

In such scenario the weak locations are not cleaned up when the object
is finalized, and will point to a free'd area.

So, during finalization and when we're sure that the object will be
destroyed for sure, check again if there are new weak locations and
unset them if any as part of the qdata destruction.
Do this adding a new utility function so that we can avoid duplicating
code to free the weak locations.

Added various tests simulating this case.

Fixes: #2390
This commit is contained in:
Marco Trevisan (Treviño) 2021-04-24 04:39:17 +02:00
parent e3e5a06d2b
commit ea68b22135
3 changed files with 221 additions and 8 deletions
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46
gobject/gobject.c
View File

@ -233,6 +233,7 @@ static guint object_floating_flag_handler (GObject *object,
static void object_interface_check_properties (gpointer check_data,
gpointer g_iface);
static void weak_locations_free_unlocked (GSList **weak_locations);
/* --- typedefs --- */
typedef struct _GObjectNotifyQueue GObjectNotifyQueue;
@ -3512,6 +3513,10 @@ g_object_unref (gpointer _object)
* established at this time, because the other thread would have
* to hold a strong ref in order to call
* g_object_add_weak_pointer() and then we wouldn't be here.
*
* Other GWeakRef's (weak locations) instead may still be added
* before the object is finalized, but in such case we'll unset
* them as part of the qdata removal.
*/
weak_locations = g_datalist_id_get_data (&object->qdata, quark_weak_locations);
@ -3533,13 +3538,8 @@ g_object_unref (gpointer _object)
/* We got the lock first, so the object will definitely die
* now. Clear out all the weak references.
*/
while (*weak_locations)
{
GWeakRef *weak_ref_location = (*weak_locations)->data;
weak_ref_location->priv.p = NULL;
*weak_locations = g_slist_delete_link (*weak_locations, *weak_locations);
}
weak_locations_free_unlocked (weak_locations);
g_datalist_id_remove_no_notify (&object->qdata, quark_weak_locations);
g_rw_lock_writer_unlock (&weak_locations_lock);
}
@ -4646,6 +4646,35 @@ g_weak_ref_get (GWeakRef *weak_ref)
return object_or_null;
}
static void
weak_locations_free_unlocked (GSList **weak_locations)
{
if (*weak_locations)
{
GSList *weak_location;
for (weak_location = *weak_locations; weak_location;)
{
GWeakRef *weak_ref_location = weak_location->data;
weak_ref_location->priv.p = NULL;
weak_location = g_slist_delete_link (weak_location, weak_location);
}
}
g_free (weak_locations);
}
static void
weak_locations_free (gpointer data)
{
GSList **weak_locations = data;
g_rw_lock_writer_lock (&weak_locations_lock);
weak_locations_free_unlocked (weak_locations);
g_rw_lock_writer_unlock (&weak_locations_lock);
}
/**
* g_weak_ref_set: (skip)
* @weak_ref: location for a weak reference
@ -4712,7 +4741,8 @@ g_weak_ref_set (GWeakRef *weak_ref,
if (weak_locations == NULL)
{
weak_locations = g_new0 (GSList *, 1);
g_datalist_id_set_data_full (&new_object->qdata, quark_weak_locations, weak_locations, g_free);
g_datalist_id_set_data_full (&new_object->qdata, quark_weak_locations,
weak_locations, weak_locations_free);
}
*weak_locations = g_slist_prepend (*weak_locations, weak_ref);

102
gobject/tests/reference.c
View File

@ -566,6 +566,106 @@ test_weak_ref (void)
g_free (dynamic_weak);
}
G_DECLARE_FINAL_TYPE (WeakReffedObject, weak_reffed_object,
WEAK, REFFED_OBJECT, GObject)
struct _WeakReffedObject
{
GObject parent;
GWeakRef *weak_ref;
};
G_DEFINE_TYPE (WeakReffedObject, weak_reffed_object, G_TYPE_OBJECT)
static void
weak_reffed_object_dispose (GObject *object)
{
WeakReffedObject *weak_reffed = WEAK_REFFED_OBJECT (object);
g_assert_cmpint (object->ref_count, ==, 1);
g_weak_ref_set (weak_reffed->weak_ref, object);
G_OBJECT_CLASS (weak_reffed_object_parent_class)->dispose (object);
}
static void
weak_reffed_object_init (WeakReffedObject *connector)
{
}
static void
weak_reffed_object_class_init (WeakReffedObjectClass *klass)
{
GObjectClass *object_class = G_OBJECT_CLASS (klass);
object_class->dispose = weak_reffed_object_dispose;
}
static void
test_weak_ref_on_dispose (void)
{
WeakReffedObject *obj;
GWeakRef weak = { { GUINT_TO_POINTER (0xDEADBEEFU) } };
g_test_bug ("https://gitlab.gnome.org/GNOME/glib/-/issues/2390");
g_test_summary ("Test that a weak ref set during dispose vfunc is cleared");
g_weak_ref_init (&weak, NULL);
obj = g_object_new (weak_reffed_object_get_type (), NULL);
obj->weak_ref = &weak;
g_assert_cmpint (G_OBJECT (obj)->ref_count, ==, 1);
g_clear_object (&obj);
g_assert_null (g_weak_ref_get (&weak));
}
static void
on_weak_ref_toggle_notify (gpointer data,
GObject *object,
gboolean is_last_ref)
{
GWeakRef *weak = data;
if (is_last_ref)
g_weak_ref_set (weak, object);
}
static void
on_weak_ref_toggle_notify_disposed (gpointer data,
GObject *object)
{
g_assert_cmpint (object->ref_count, ==, 1);
g_object_ref (object);
g_object_unref (object);
}
static void
test_weak_ref_on_toggle_notify (void)
{
GObject *obj;
GWeakRef weak = { { GUINT_TO_POINTER (0xDEADBEEFU) } };
g_test_bug ("https://gitlab.gnome.org/GNOME/glib/-/issues/2390");
g_test_summary ("Test that a weak ref set on toggle notify is cleared");
g_weak_ref_init (&weak, NULL);
obj = g_object_new (G_TYPE_OBJECT, NULL);
g_object_add_toggle_ref (obj, on_weak_ref_toggle_notify, &weak);
g_object_weak_ref (obj, on_weak_ref_toggle_notify_disposed, NULL);
g_object_unref (obj);
g_assert_cmpint (obj->ref_count, ==, 1);
g_clear_object (&obj);
g_assert_null (g_weak_ref_get (&weak));
}
typedef struct
{
gboolean should_be_last;
@ -826,6 +926,8 @@ main (int argc, char **argv)
g_test_add_func ("/object/weak-pointer/set", test_weak_pointer_set);
g_test_add_func ("/object/weak-pointer/set-function", test_weak_pointer_set_function);
g_test_add_func ("/object/weak-ref", test_weak_ref);
g_test_add_func ("/object/weak-ref/on-dispose", test_weak_ref_on_dispose);
g_test_add_func ("/object/weak-ref/on-toggle-notify", test_weak_ref_on_toggle_notify);
g_test_add_func ("/object/toggle-ref", test_toggle_ref);
g_test_add_func ("/object/qdata", test_object_qdata);
g_test_add_func ("/object/qdata2", test_object_qdata2);

81
gobject/tests/threadtests.c
View File

@ -343,6 +343,85 @@ test_threaded_weak_ref (void)
get_wins, unref_wins);
}
typedef struct
{
GObject *object;
GWeakRef *weak;
gint started; /* (atomic) */
gint finished; /* (atomic) */
gint disposing; /* (atomic) */
} ThreadedWeakRefData;
static void
on_weak_ref_disposed (gpointer data,
GObject *gobj)
{
ThreadedWeakRefData *thread_data = data;
/* Wait until the thread has started */
while (!g_atomic_int_get (&thread_data->started))
continue;
g_atomic_int_set (&thread_data->disposing, 1);
/* Wait for the thread to act, so that the object is still valid */
while (!g_atomic_int_get (&thread_data->finished))
continue;
g_atomic_int_set (&thread_data->disposing, 0);
}
static gpointer
on_other_thread_weak_ref (gpointer user_data)
{
ThreadedWeakRefData *thread_data = user_data;
GObject *object = thread_data->object;
g_atomic_int_set (&thread_data->started, 1);
/* Ensure we've started disposal */
while (!g_atomic_int_get (&thread_data->disposing))
continue;
g_object_ref (object);
g_weak_ref_set (thread_data->weak, object);
g_object_unref (object);
g_assert_cmpint (thread_data->disposing, ==, 1);
g_atomic_int_set (&thread_data->finished, 1);
return NULL;
}
static void
test_threaded_weak_ref_finalization (void)
{
GObject *obj = g_object_new (G_TYPE_OBJECT, NULL);
GWeakRef weak = { { GUINT_TO_POINTER (0xDEADBEEFU) } };
ThreadedWeakRefData thread_data = {
.object = obj, .weak = &weak, .started = 0, .finished = 0
};
g_test_bug ("https://gitlab.gnome.org/GNOME/glib/-/issues/2390");
g_test_summary ("Test that a weak ref added by another thread during dispose "
"of a GObject is cleared during finalisation. "
"Use on_weak_ref_disposed() to synchronize the other thread "
"with the dispose vfunc.");
g_weak_ref_init (&weak, NULL);
g_object_weak_ref (obj, on_weak_ref_disposed, &thread_data);
g_assert_cmpint (obj->ref_count, ==, 1);
g_thread_unref (g_thread_new ("on_other_thread",
on_other_thread_weak_ref,
&thread_data));
g_object_unref (obj);
/* This is what this test is about: at this point the weak reference
* should have been unset (and not point to a dead object either). */
g_assert_null (g_weak_ref_get (&weak));
}
int
main (int argc,
char *argv[])
@ -352,6 +431,8 @@ main (int argc,
/* g_test_add_func ("/GObject/threaded-class-init", test_threaded_class_init); */
g_test_add_func ("/GObject/threaded-object-init", test_threaded_object_init);
g_test_add_func ("/GObject/threaded-weak-ref", test_threaded_weak_ref);
g_test_add_func ("/GObject/threaded-weak-ref/on-finalization",
test_threaded_weak_ref_finalization);
return g_test_run();
}