[PATCH wayland v2] event-loop: Dispatch idle callbacks twice

[Giulio Camuffo]

2015-01-28 17:25 GMT+02:00 Derek Foreman <derekf at osg.samsung.com>:
> To fix a shutdown crash in weston's x11 compositor I want to move the
> weston X window close to an idle handler.
>
> Since idle handlers are processed at the start of an event loop, the
> handler that deals with window close will run at the start of the
> next input_loop dispatch, after which the dispatcher blocks on epoll
> forever (since all input events that will ever occur have been consumed).
>
> Dispatching idle callbacks both at the start and end of event-loop
> processing will prevent this permanent blocking.
>
> Note that just moving the callback dispatch could theoretically
> result in an idle callback being delayed indefinitely while waiting
> for epoll_wait() to complete.
>
> Callbacks are removed from the list when they're run, so the second
> dispatch won't result in any extra calls.
>
> Signed-off-by: Derek Foreman <derekf at osg.samsung.com>
> ---
>
> Amusingly, the problem Bill points out is exactly the problem this patch is
> trying to correct.
>
> This version of the patch leaves the original dispatch and adds a second.
>
>
>  src/event-loop.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/src/event-loop.c b/src/event-loop.c
> index 1f571ba..d257d78 100644
> --- a/src/event-loop.c
> +++ b/src/event-loop.c
> @@ -421,10 +421,12 @@ wl_event_loop_dispatch(struct wl_event_loop *loop, int timeout)
>
>         wl_event_loop_process_destroy_list(loop);
>
> +       wl_event_loop_dispatch_idle(loop);
> +

How does this fix the problem? The idle callbacks are still called
before the epoll_wait(), so shouldn't the problem you describe in the
commit message still happen?
Besides, the idle callbacks are anyway going to be called very soon at
the next loop in wl_display_run() after wl_event_loop_dispatch()
returns. Or is the post_dispatch_check() call below involved somehow?


--
Giulio

>         do {
>                 n = post_dispatch_check(loop);
>         } while (n > 0);
> -
> +
>         return 0;
>  }
>
> --
> 2.1.4
>
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