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Merge branch 'gsettingsbackend-thread-safe-watches' into 'master'

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GSettingsBackend - Fix thread-safety during destruction of GSettings instances...

Closes #1870

See merge request GNOME/glib!1040
This commit is contained in:
Philip Withnall 2019-08-27 09:35:21 +00:00
commit 68b4dfd430
1 changed files with 24 additions and 17 deletions
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41
gio/gsettingsbackend.c
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@ -122,7 +122,13 @@ is_path (const gchar *path)
struct _GSettingsBackendWatch
{
GObject *target;
/* Always access the target via the weak reference */
GWeakRef target;
/* The pointer is only for comparison from the weak notify,
* at which point the target might already be close to
* destroyed. It's not safe to use it for anything anymore
* at that point */
GObject *target_ptr;
const GSettingsListenerVTable *vtable;
GMainContext *context;
GSettingsBackendWatch *next;
@ -137,7 +143,7 @@ struct _GSettingsBackendClosure
gchar **names);
GMainContext *context;
GWeakRef *target_ref;
GObject *target;
GSettingsBackend *backend;
gchar *name;
gpointer origin_tag;
@ -154,11 +160,12 @@ g_settings_backend_watch_weak_notify (gpointer data,
/* search and remove */
g_mutex_lock (&backend->priv->lock);
for (ptr = &backend->priv->watches; *ptr; ptr = &(*ptr)->next)
if ((*ptr)->target == where_the_object_was)
if ((*ptr)->target_ptr == where_the_object_was)
{
GSettingsBackendWatch *tmp = *ptr;
*ptr = tmp->next;
g_weak_ref_clear (&tmp->target);
g_slice_free (GSettingsBackendWatch, tmp);
g_mutex_unlock (&backend->priv->lock);
@ -208,9 +215,10 @@ g_settings_backend_watch (GSettingsBackend *backend,
* GSettings object in a thread other than the one that is doing the
* dispatching is as follows:
*
* 1) hold a thread-safe GWeakRef on the GSettings during an outstanding
* 1) hold a strong reference on the GSettings during an outstanding
* dispatch. This ensures that the delivery is always possible while
* the GSettings object is alive.
* the GSettings object is alive, and if this was the last reference
* then it will be dropped from the dispatch thread.
*
* 2) hold a weak reference on the GSettings at other times. This
* allows us to receive early notification of pending destruction
@ -235,7 +243,8 @@ g_settings_backend_watch (GSettingsBackend *backend,
watch = g_slice_new (GSettingsBackendWatch);
watch->context = context;
watch->vtable = vtable;
watch->target = target;
g_weak_ref_init (&watch->target, target);
watch->target_ptr = target;
g_object_weak_ref (target, g_settings_backend_watch_weak_notify, backend);
/* linked list prepend */
@ -260,20 +269,14 @@ static gboolean
g_settings_backend_invoke_closure (gpointer user_data)
{
GSettingsBackendClosure *closure = user_data;
GObject *target = g_weak_ref_get (closure->target_ref);
if (target)
{
closure->function (target, closure->backend, closure->name,
closure->origin_tag, closure->names);
g_object_unref (target);
}
closure->function (closure->target, closure->backend, closure->name,
closure->origin_tag, closure->names);
if (closure->context)
g_main_context_unref (closure->context);
g_object_unref (closure->backend);
g_weak_ref_clear (closure->target_ref);
g_free (closure->target_ref);
g_object_unref (closure->target);
g_strfreev (closure->names);
g_free (closure->name);
@ -304,14 +307,18 @@ g_settings_backend_dispatch_signal (GSettingsBackend *backend,
for (watch = backend->priv->watches; watch; watch = watch->next)
{
GSettingsBackendClosure *closure;
GObject *target = g_weak_ref_get (&watch->target);
/* If the target was destroyed in the meantime, just skip it here */
if (!target)
continue;
closure = g_slice_new (GSettingsBackendClosure);
closure->context = watch->context;
if (closure->context)
g_main_context_ref (closure->context);
closure->backend = g_object_ref (backend);
closure->target_ref = g_new (GWeakRef, 1);
g_weak_ref_init (closure->target_ref, watch->target);
closure->target = g_steal_pointer (&target);
closure->function = G_STRUCT_MEMBER (void *, watch->vtable,
function_offset);
closure->name = g_strdup (name);