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

[Giulio Camuffo]

Forgot the

Reviewed-by: Giulio Camuffo <giuliocamuffo at gmail.com>


2015-01-28 17:58 GMT+02:00 Giulio Camuffo <giuliocamuffo at gmail.com>:
> 2015-01-28 17:49 GMT+02:00 Derek Foreman <derekf at osg.samsung.com>:
>> On 28/01/15 09:39 AM, Giulio Camuffo wrote:
>>> 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?
>>
>> The callback in question is added by the handler
>> source->interface->dispatch() calls in the middle.  :)
>>
>> So the second idle dispatch gets it, and the loop isn't entered again.
>>
>> Without the change it won't get called until the loop is entered, and
>> there's no events left to process, so epoll_wait() just sits...
>
> Ah, so the loop is broken and wl_display_run() returns after the
> current iteration. Looks good then.
>
>>
>>> --
>>> Giulio
>>>
>>>>         do {
>>>>                 n = post_dispatch_check(loop);
>>>>         } while (n > 0);
>>>> -
>>>> +
>>>>         return 0;
>>>>  }
>>>>
>>>> --
>>>> 2.1.4
>>>>
>>>> _______________________________________________
>>>> wayland-devel mailing list
>>>> wayland-devel at lists.freedesktop.org
>>>> http://lists.freedesktop.org/mailman/listinfo/wayland-devel
>>