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server: introduce wl_signal_emit_mutable

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wl_signal_emit doesn't handle well situations where a listener removes
another listener. This can happen in practice: wlroots and Weston [1]
both have private helpers to workaround this defect.

wl_signal_emit can't be fixed without breaking the API. Instead,
introduce a new function. Callers need to make sure to always remove
listeners when they are free'd.

[1]: https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/457

Signed-off-by: Simon Ser <contact@emersion.fr>
Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>
This commit is contained in:
Simon Ser 2022-01-31 23:09:26 +01:00
parent 868eb99eb0
commit 962aefda42
3 changed files with 107 additions and 0 deletions
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41
tests/signal-test.c
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@ -115,3 +115,44 @@ TEST(signal_emit_to_more_listeners)
assert(3 * counter == count);
}
struct signal_emit_mutable_data {
int count;
struct wl_listener *remove_listener;
};
static void
signal_notify_mutable(struct wl_listener *listener, void *data)
{
struct signal_emit_mutable_data *test_data = data;
test_data->count++;
}
static void
signal_notify_and_remove_mutable(struct wl_listener *listener, void *data)
{
struct signal_emit_mutable_data *test_data = data;
signal_notify_mutable(listener, test_data);
wl_list_remove(&test_data->remove_listener->link);
}
TEST(signal_emit_mutable)
{
struct signal_emit_mutable_data data = {0};
/* l2 will remove l3 before l3 is notified */
struct wl_signal signal;
struct wl_listener l1 = {.notify = signal_notify_mutable};
struct wl_listener l2 = {.notify = signal_notify_and_remove_mutable};
struct wl_listener l3 = {.notify = signal_notify_mutable};
wl_signal_init(&signal);
wl_signal_add(&signal, &l1);
wl_signal_add(&signal, &l2);
wl_signal_add(&signal, &l3);
data.remove_listener = &l3;
wl_signal_emit_mutable(&signal, &data);
assert(data.count == 2);
}