> In the past much code (weston, efl/enlightenment, mutter) has > freed structures containing wl_listeners from destroy handlers > without first removing the listener from the signal. As the > destroy notifier only fires once, this has largely gone > unnoticed until recently. > > Other code does not (Qt, wlroots) - and removes itself from > the signal before free. > > If somehow a destroy signal is listened to by code from both > kinds of callers, those that free will corrupt the lists for > those that don't, and Bad Things will happen. > > To avoid these bad things, remove every item from the signal list > during destroy emit, and put it in a list all its own. This way > whether the listener is removed or not has no impact on the > following emits. > > Signed-off-by: Derek Foreman <der...@osg.samsung.com>
Thanks for looking into this, I think it's a great idea to add this behaviour to the ABI. This patch LGTM. Reviewed-by: Simon Ser <cont...@emersion.fr> > --- > > Changes since v1: > In v1 I went through some ugly steps to ensure wl_priv_signal_get() > worked. It seems this is actually a useless requirement, and the > code is prettier without it. > > src/wayland-private.h | 3 +++ > src/wayland-server.c | 46 +++++++++++++++++++++++++++++++++++++++++++--- > 2 files changed, 46 insertions(+), 3 deletions(-) > > diff --git a/src/wayland-private.h b/src/wayland-private.h > index 12b9032..29516ec 100644 > --- a/src/wayland-private.h > +++ b/src/wayland-private.h > @@ -253,6 +253,9 @@ wl_priv_signal_get(struct wl_priv_signal *signal, > wl_notify_func_t notify); > void > wl_priv_signal_emit(struct wl_priv_signal *signal, void *data); > > +void > +wl_priv_signal_final_emit(struct wl_priv_signal *signal, void *data); > + > void > wl_connection_close_fds_in(struct wl_connection *connection, int max); > > diff --git a/src/wayland-server.c b/src/wayland-server.c > index eb1e500..8c3b800 100644 > --- a/src/wayland-server.c > +++ b/src/wayland-server.c > @@ -682,7 +682,7 @@ destroy_resource(void *element, void *data, uint32_t > flags) > /* Don't emit the new signal for deprecated resources, as that would > * access memory outside the bounds of the deprecated struct */ > if (!resource_is_deprecated(resource)) > - wl_priv_signal_emit(&resource->destroy_signal, resource); > + wl_priv_signal_final_emit(&resource->destroy_signal, resource); > > if (resource->destroy) > resource->destroy(resource); > @@ -841,7 +841,7 @@ wl_client_destroy(struct wl_client *client) > { > uint32_t serial = 0; > > - wl_priv_signal_emit(&client->destroy_signal, client); > + wl_priv_signal_final_emit(&client->destroy_signal, client); > > wl_client_flush(client); > wl_map_for_each(&client->objects, destroy_resource, &serial); > @@ -1089,7 +1089,7 @@ wl_display_destroy(struct wl_display *display) > struct wl_socket *s, *next; > struct wl_global *global, *gnext; > > - wl_priv_signal_emit(&display->destroy_signal, display); > + wl_priv_signal_final_emit(&display->destroy_signal, display); > > wl_list_for_each_safe(s, next, &display->socket_list, link) { > wl_socket_destroy(s); > @@ -2025,6 +2025,46 @@ wl_priv_signal_emit(struct wl_priv_signal *signal, > void *data) > } > } > > +/** Emit the signal for the last time, calling all the installed listeners > + * > + * Iterate over all the listeners added to this \a signal and call > + * their \a notify function pointer, passing on the given \a data. > + * Removing or adding a listener from within wl_priv_signal_emit() > + * is safe, as is freeing the structure containing the listener. > + * > + * A large body of external code assumes it's ok to free a destruction > + * listener without removing that listener from the list. Mixing code > + * that acts like this and code that doesn't will result in list > + * corruption. > + * > + * We resolve this by removing each item from the list and isolating it > + * in another list. We discard it completely after firing the notifier. > + * This should allow interoperability between code that unlinks its > + * destruction listeners and code that just frees structures they're in. > + * > + */ > +void > +wl_priv_signal_final_emit(struct wl_priv_signal *signal, void *data) > +{ > + struct wl_listener *l; > + struct wl_list *pos; > + > + /* During a destructor notifier isolate every list item before > + * notifying. This renders harmless the long standing misuse > + * of freeing listeners without removing them, but allows > + * callers that do choose to remove them to interoperate with > + * ones that don't. */ > + while (!wl_list_empty(&signal->listener_list)) { > + pos = signal->listener_list.next; > + l = wl_container_of(pos, l, link); > + > + wl_list_remove(pos); > + wl_list_init(pos); > + > + l->notify(l, data); > + } > +} > + > /** \endcond INTERNAL */ > > /** \cond */ /* Deprecated functions below. */ > -- > 2.14.3 > > _______________________________________________ > wayland-devel mailing list > wayland-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/wayland-devel _______________________________________________ wayland-devel mailing list wayland-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/wayland-devel