Add wlr_signal_emit_safe

2 files changed, 35 insertions, 0 deletions

diff --git a/util/meson.build b/util/meson.build
index 34aa428b..adc52a53 100644
--- a/util/meson.build
+++ b/util/meson.build
@@ -4,6 +4,7 @@ lib_wlr_util = static_library(
 		'log.c',
 		'os-compatibility.c',
 		'region.c',
+		'signal.c',
 	),
 	include_directories: wlr_inc,
 	dependencies: [wayland_server, pixman],
diff --git a/util/signal.c b/util/signal.c
new file mode 100644
index 00000000..91c4f571
--- /dev/null
+++ b/util/signal.c
@@ -0,0 +1,34 @@
+#include <wlr/util/signal.h>
+
+static void handle_noop(struct wl_listener *listener, void *data) {
+	// Do nothing
+}
+
+void wlr_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);
+}