[PATCH] server: add wl_signal_emit_safe
Simon Ser
contact at emersion.fr
Fri Jul 13 21:40:42 UTC 2018
This new function allows listeners to remove themselves or any
other listener when called. This version only works if listeners
are properly cleaned up when the wl_signal is free'd.
Signed-off-by: Simon Ser <contact at emersion.fr>
---
This is a [1] follow-up. Since we noticed the previous version is
not a drop-in replacement for wl_signal_emit, this patch just adds
a new function instead.
[1]: https://patchwork.freedesktop.org/patch/204641/
src/wayland-server-core.h | 3 ++
src/wayland-server.c | 47 +++++++++++++++++++++
tests/signal-test.c | 86 +++++++++++++++++++++++++++++++++++++++
3 files changed, 136 insertions(+)
diff --git a/src/wayland-server-core.h b/src/wayland-server-core.h
index 2e725d9..4a2948a 100644
--- a/src/wayland-server-core.h
+++ b/src/wayland-server-core.h
@@ -468,6 +468,9 @@ wl_signal_emit(struct wl_signal *signal, void *data)
l->notify(l, data);
}
+void
+wl_signal_emit_safe(struct wl_signal *signal, void *data);
+
typedef void (*wl_resource_destroy_func_t)(struct wl_resource *resource);
/*
diff --git a/src/wayland-server.c b/src/wayland-server.c
index eae8d2e..a5f3735 100644
--- a/src/wayland-server.c
+++ b/src/wayland-server.c
@@ -1932,6 +1932,53 @@ wl_client_for_each_resource(struct wl_client *client,
wl_map_for_each(&client->objects, resource_iterator_helper, &context);
}
+static void
+handle_noop(struct wl_listener *listener, void *data) {
+ /* Do nothing */
+}
+
+/** Emits this signal, safe against removal of any listener.
+ *
+ * \note This function can only be used if listeners are properly removed when
+ * the wl_signal is free'd.
+ *
+ * \param signal The signal object that will emit the signal
+ * \param data The data that will be emitted with the signal
+ *
+ * \sa wl_signal_emit()
+ *
+ * \memberof wl_signal
+ */
+WL_EXPORT void
+wl_signal_emit_safe(struct wl_signal *signal, void *data) {
+ struct wl_listener cursor;
+ struct wl_listener end;
+
+ /* Add two special markers: one cursor and one end marker. This way, we know
+ * that we've already called listeners on the left of the cursor and that we
+ * don't want to call listeners on the right of the end marker. The 'it'
+ * function can remove any element it wants from the list without troubles.
+ * wl_list_for_each_safe tries to be safe but it fails: it works fine
+ * if the current item is removed, but not if the next one is. */
+ wl_list_insert(&signal->listener_list, &cursor.link);
+ cursor.notify = handle_noop;
+ wl_list_insert(signal->listener_list.prev, &end.link);
+ end.notify = handle_noop;
+
+ while (cursor.link.next != &end.link) {
+ struct wl_list *pos = cursor.link.next;
+ struct wl_listener *l = wl_container_of(pos, l, link);
+
+ wl_list_remove(&cursor.link);
+ wl_list_insert(pos, &cursor.link);
+
+ l->notify(l, data);
+ }
+
+ wl_list_remove(&cursor.link);
+ wl_list_remove(&end.link);
+}
+
/** \cond INTERNAL */
/** Initialize a wl_priv_signal object
diff --git a/tests/signal-test.c b/tests/signal-test.c
index 7bbaa9f..dc762a4 100644
--- a/tests/signal-test.c
+++ b/tests/signal-test.c
@@ -115,3 +115,89 @@ TEST(signal_emit_to_more_listeners)
assert(3 * counter == count);
}
+
+struct signal
+{
+ struct wl_signal signal;
+ struct wl_listener l1, l2, l3;
+ int count;
+ struct wl_listener *current;
+};
+
+static void notify_remove(struct wl_listener *l, void *data)
+{
+ struct signal *sig = data;
+ wl_list_remove(&sig->current->link);
+ wl_list_init(&sig->current->link);
+ sig->count++;
+}
+
+#define INIT \
+ wl_signal_init(&signal.signal); \
+ wl_list_init(&signal.l1.link); \
+ wl_list_init(&signal.l2.link); \
+ wl_list_init(&signal.l3.link);
+#define CHECK_EMIT(expected) \
+ signal.count = 0; \
+ wl_signal_emit_safe(&signal.signal, &signal); \
+ assert(signal.count == expected);
+
+TEST(signal_remove_listener)
+{
+ test_set_timeout(4);
+
+ struct signal signal;
+
+ signal.l1.notify = notify_remove;
+ signal.l2.notify = notify_remove;
+ signal.l3.notify = notify_remove;
+
+ INIT
+ wl_signal_add(&signal.signal, &signal.l1);
+
+ signal.current = &signal.l1;
+ CHECK_EMIT(1)
+ CHECK_EMIT(0)
+
+ INIT
+ wl_signal_add(&signal.signal, &signal.l1);
+ wl_signal_add(&signal.signal, &signal.l2);
+
+ CHECK_EMIT(2)
+ CHECK_EMIT(1)
+
+ INIT
+ wl_signal_add(&signal.signal, &signal.l1);
+ wl_signal_add(&signal.signal, &signal.l2);
+
+ signal.current = &signal.l2;
+ CHECK_EMIT(1)
+ CHECK_EMIT(1)
+
+ INIT
+ wl_signal_add(&signal.signal, &signal.l1);
+ wl_signal_add(&signal.signal, &signal.l2);
+ wl_signal_add(&signal.signal, &signal.l3);
+
+ signal.current = &signal.l1;
+ CHECK_EMIT(3)
+ CHECK_EMIT(2)
+
+ INIT
+ wl_signal_add(&signal.signal, &signal.l1);
+ wl_signal_add(&signal.signal, &signal.l2);
+ wl_signal_add(&signal.signal, &signal.l3);
+
+ signal.current = &signal.l2;
+ CHECK_EMIT(2)
+ CHECK_EMIT(2)
+
+ INIT
+ wl_signal_add(&signal.signal, &signal.l1);
+ wl_signal_add(&signal.signal, &signal.l2);
+ wl_signal_add(&signal.signal, &signal.l3);
+
+ signal.current = &signal.l3;
+ CHECK_EMIT(2)
+ CHECK_EMIT(2)
+}
--
2.18.0
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