util: add wlr_output_destroy_safe

This adds a generic helper to destory transient globals.

See [1]. This patch depends on [2] and [3].

[1]: https://gitlab.freedesktop.org/wayland/wayland/issues/10
[2]: https://gitlab.freedesktop.org/wayland/wayland/merge_requests/28
[3]: https://gitlab.freedesktop.org/wayland/wayland/merge_requests/30

include/util/global.h

@@ -0,0 +1,15 @@
+#ifndef UTIL_GLOBAL_H
+#define UTIL_GLOBAL_H
+
+#include <wayland-server-core.h>
+
+/**
+ * Destroy a transient global.
+ *
+ * Globals that are created and destroyed on the fly need special handling to
+ * prevent race conditions with wl_registry. Use this function to destroy them.
+ */
+void wlr_global_destroy_safe(struct wl_global *global,
+	struct wl_display *display);
+
+#endif

util/global.c

@@ -0,0 +1,43 @@
+#include <stdlib.h>
+#include "util/global.h"
+
+struct destroy_global_data {
+	struct wl_global *global;
+	struct wl_event_source *event_source;
+};
+
+static int destroy_global(void *_data) {
+	struct destroy_global_data *data = _data;
+	wl_global_destroy(data->global);
+	wl_event_source_remove(data->event_source);
+	free(data);
+	return 0;
+}
+
+void wlr_global_destroy_safe(struct wl_global *global,
+		struct wl_display *display) {
+	// Don't destroy the global immediately. If the global has been created
+	// recently, clients might try to bind to it after we've destroyed it.
+	// Instead, remove the global so that clients stop seeing it and wait an
+	// arbitrary amount of time before destroying the global as a workaround.
+	// See: https://gitlab.freedesktop.org/wayland/wayland/issues/10
+
+	wl_global_remove(global);
+	wl_global_set_user_data(global, NULL); // safety net
+
+	struct wl_event_loop *event_loop = wl_display_get_event_loop(display);
+	struct destroy_global_data *data = calloc(1, sizeof(*data));
+	if (data == NULL) {
+		wl_global_destroy(global);
+		return;
+	}
+	data->global = global;
+	data->event_source =
+		wl_event_loop_add_timer(event_loop, destroy_global, data);
+	if (data->event_source == NULL) {
+		free(data);
+		wl_global_destroy(global);
+		return;
+	}
+	wl_event_source_timer_update(data->event_source, 5000);
+}

util/meson.build

@@ -1,5 +1,6 @@
 wlr_files += files(
 	'array.c',
+	'global.c',
 	'log.c',
 	'region.c',
 	'shm.c',

wlroots.syms

@@ -6,5 +6,6 @@
 		_wlr_strip_path;
 	local:
 		wlr_signal_emit_safe;
+		wlr_global_destroy_safe;
 		*;
 };