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compositor-wayland: avoid recursive dispatch with wl_outputs

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Calling wl_display_roundtrip() from within a Wayland event handler means
we will re-enter event dispatch, that is, it will lead to recursive
dispatch. Even if libwayland-client was safe, this would lead to
unexpected code paths: the first event handler function has not returned
when other event handler functions may get called. In this particular
case it maybe didn't hurt, but it's still a fragile pattern to use.

Replace the wl_display_roundtrip() with a manual sync callback to do the
work.

This does not break the wayland-backend initialization sequence, because
sprawl_across_outputs was set only after the roundtrip to ensure
wl_registry globals have been received so the code would not have been
hit anyway, and weston_backend_init() also has a second roundtrip that
ensures the per wl_output events have been received before continuing.

For wayland-backend output hotplug the change is insignificant because
it will only delay the output creation a bit, and the parent outputs are
not processed anywhere in between.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>
Acked-by: Daniel Stone <daniels@collabora.com>
This commit is contained in:
Pekka Paalanen 2017-10-19 12:03:06 +03:00
parent aedcd8ebb0
commit b07de934cc
1 changed files with 28 additions and 2 deletions
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30
libweston/compositor-wayland.c
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@ -136,6 +136,7 @@ struct wayland_output {
};
struct wayland_parent_output {
struct wayland_backend *backend; /**< convenience */
struct wayland_output *output;
struct wl_list link;
@ -153,6 +154,8 @@ struct wayland_parent_output {
uint32_t transform;
uint32_t scale;
struct wl_callback *sync_cb; /**< wl_output < 2 done replacement */
struct wl_list mode_list;
struct weston_mode *preferred_mode;
struct weston_mode *current_mode;
@ -2258,6 +2261,24 @@ static const struct wl_output_listener output_listener = {
wayland_parent_output_mode
};
static void
output_sync_callback(void *data, struct wl_callback *callback, uint32_t unused)
{
struct wayland_parent_output *output = data;
assert(output->sync_cb == callback);
wl_callback_destroy(callback);
output->sync_cb = NULL;
assert(output->backend->sprawl_across_outputs);
wayland_output_create_for_parent_output(output->backend, output);
}
static const struct wl_callback_listener output_sync_listener = {
output_sync_callback
};
static void
wayland_backend_register_output(struct wayland_backend *b, uint32_t id)
{
@ -2267,6 +2288,7 @@ wayland_backend_register_output(struct wayland_backend *b, uint32_t id)
if (!output)
return;
output->backend = b;
output->id = id;
output->global = wl_registry_bind(b->parent.registry, id,
&wl_output_interface, 1);
@ -2284,8 +2306,9 @@ wayland_backend_register_output(struct wayland_backend *b, uint32_t id)
wl_list_insert(&b->parent.output_list, &output->link);
if (b->sprawl_across_outputs) {
wl_display_roundtrip(b->parent.wl_display);
wayland_output_create_for_parent_output(b, output);
output->sync_cb = wl_display_sync(b->parent.wl_display);
wl_callback_add_listener(output->sync_cb,
&output_sync_listener, output);
}
}
@ -2294,6 +2317,9 @@ wayland_parent_output_destroy(struct wayland_parent_output *output)
{
struct weston_mode *mode, *next;
if (output->sync_cb)
wl_callback_destroy(output->sync_cb);
if (output->output)
wayland_output_destroy(&output->output->base);