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GSettingsBackend: use a GWeakRef during dispatch

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Instead of a full reference, which causes problems for clients that
expect a GSettings instance to stop firing signals once they drop the
last reference.

https://bugzilla.gnome.org/show_bug.cgi?id=780861
This commit is contained in:
Cosimo Cecchi 2017-08-27 12:15:37 -07:00
parent 61cb8b232b
commit 88a39670e7
1 changed files with 21 additions and 13 deletions
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34
gio/gsettingsbackend.c
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@ -137,7 +137,7 @@ struct _GSettingsBackendClosure
gchar **names);
GMainContext *context;
GObject *target;
GWeakRef *target_ref;
GSettingsBackend *backend;
gchar *name;
gpointer origin_tag;
@ -208,8 +208,9 @@ 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 GObject reference on the GSettings during an outstanding
* dispatch. This ensures that the delivery is always possible.
* 1) hold a thread-safe GWeakRef on the GSettings during an outstanding
* dispatch. This ensures that the delivery is always possible while
* the GSettings object is alive.
*
* 2) hold a weak reference on the GSettings at other times. This
* allows us to receive early notification of pending destruction
@ -224,12 +225,8 @@ g_settings_backend_watch (GSettingsBackend *backend,
* possible to keep the object alive using g_object_ref() and we would
* have no way of knowing this.
*
* Note also that we do not need to hold a reference on the main
* context here since the GSettings instance does that for us and we
* will receive the weak notify long before it is dropped. We don't
* even need to hold it during dispatches because our reference on the
* GSettings will prevent the finalize from running and dropping the
* ref on the context.
* Note also that we need to hold a reference on the main context here
* since the GSettings instance may be finalized before the closure runs.
*
* All access to the list holds a mutex. We have some strategies to
* avoid some of the pain that would be associated with that.
@ -263,12 +260,20 @@ static gboolean
g_settings_backend_invoke_closure (gpointer user_data)
{
GSettingsBackendClosure *closure = user_data;
GObject *target = g_weak_ref_get (closure->target_ref);
closure->function (closure->target, closure->backend, closure->name,
closure->origin_tag, closure->names);
if (target)
{
closure->function (target, closure->backend, closure->name,
closure->origin_tag, closure->names);
g_object_unref (target);
}
if (closure->context)
g_main_context_unref (closure->context);
g_object_unref (closure->backend);
g_object_unref (closure->target);
g_weak_ref_clear (closure->target_ref);
g_free (closure->target_ref);
g_strfreev (closure->names);
g_free (closure->name);
@ -302,8 +307,11 @@ g_settings_backend_dispatch_signal (GSettingsBackend *backend,
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 = g_object_ref (watch->target);
closure->target_ref = g_new (GWeakRef, 1);
g_weak_ref_init (closure->target_ref, watch->target);
closure->function = G_STRUCT_MEMBER (void *, watch->vtable,
function_offset);
closure->name = g_strdup (name);