[PATCH weston] compositor-x11: Move the x11 event handler to the display loop

[Derek Foreman]

On 19/12/14 06:40 AM, Pekka Paalanen wrote:
> On Fri, 12 Dec 2014 14:29:42 -0600
> Derek Foreman <derekf at osg.samsung.com> wrote:
> 
>> I just noticed that the follow patch *exactly* undoes commit 22ba60e
>>
>> Is there any other reason that commit was necessary, or was it intended
>> to be cosmetic?
> 
> No, I don't think it was meant to be cosmetic.
> 
> There is some fancy input scheduling going on with the repaint loop, so
> that input events would be sent as a burst to the clients when the
> compositor is spinning in the repaint loop. The idea is that because
> clients repaint only once per cycle, they don't need to be woken up due
> to input any more often than that. Or that's how I understood it.
> 
> The problem here, I assume, is that the X11 fd is not only input, but
> also output events, unlike DRM backend where the DRM fd is separate.
> 
> I would be inclined to just take this patch, because it fixes a bug and
> the x11 backend is of lesser quality anyway.

Hmmm, I think the only event that matters is XCB_CLIENT_MESSAGE (delete
window).  Can't I just handle that from an idle callback?

> But, I also wonder, if reading the evdev fds in DRM backend only once
> per cycle could cause the kernel input buffers to overflow in some cases
> (gaming mice?), leading to lost input events?

Well, I get a lot of dropped events with the pixman renderer and a
1000hz mouse if I start rotating a few windows, but I think that's not
going to go away unless input ends up in its own thread.

> 
> Thanks,
> pq
> 
>> On 12/12/14 02:12 PM, Derek Foreman wrote:
>>> While it conceptually makes sense to put the x11 event handler
>>> in the compositor "input" loop, the input loop is actually
>>> dispatched in the middle of the frame repaint.  When the
>>> X11 event results in closing the compositor, this can cause
>>> the current output to be destroyed just prior to trying to
>>> process animations on it.
>>>
>>> Closes bug: https://bugs.freedesktop.org/show_bug.cgi?id=81314
>>>
>>> Signed-off-by: Derek Foreman <derekf at osg.samsung.com>
>>> ---
>>>  src/compositor-x11.c | 4 +++-
>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/src/compositor-x11.c b/src/compositor-x11.c
>>> index a760f33..cf39ad7 100644
>>> --- a/src/compositor-x11.c
>>> +++ b/src/compositor-x11.c
>>> @@ -1455,6 +1455,7 @@ x11_compositor_create(struct wl_display *display,
>>>  	struct x11_compositor *c;
>>>  	struct x11_output *output;
>>>  	struct weston_config_section *section;
>>> +	struct wl_event_loop *loop;
>>>  	xcb_screen_iterator_t s;
>>>  	int i, x = 0, output_count = 0;
>>>  	int width, height, scale, count;
>>> @@ -1580,8 +1581,9 @@ x11_compositor_create(struct wl_display *display,
>>>  		x = pixman_region32_extents(&output->base.region)->x2;
>>>  	}
>>>  
>>> +	loop = wl_display_get_event_loop(c->base.wl_display);
>>>  	c->xcb_source =
>>> -		wl_event_loop_add_fd(c->base.input_loop,
>>> +		wl_event_loop_add_fd(loop,
>>>  				     xcb_get_file_descriptor(c->conn),
>>>  				     WL_EVENT_READABLE,
>>>  				     x11_compositor_handle_event, c);
>>>
>>
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>