[cairo] [PATCH 2/2] xlib: Call XSync() before ignoring errors

[Uli Schlachter]

On 07.03.2017 11:31, Chris Wilson wrote:
> On Tue, Mar 07, 2017 at 11:21:31AM +0100, Uli Schlachter wrote:
>> The code here wants to ignore errors for a specific request. To do so,
>> it sets a no-op error handler. However, it could happen that some
>> previous request caused an error and this error will also be ignored by
>> the no-op error handler.
>>
>> To avoid this, call XSync() before setting the error handler. This makes
>> sure that all pending errors are handled.
>>
>> Signed-off-by: Uli Schlachter <psychon at znc.in>
>> ---
>>  src/cairo-xlib-surface.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/src/cairo-xlib-surface.c b/src/cairo-xlib-surface.c
>> index 84e7c8e49..908d76daf 100644
>> --- a/src/cairo-xlib-surface.c
>> +++ b/src/cairo-xlib-surface.c
>> @@ -787,6 +787,7 @@ _get_image_surface (cairo_xlib_surface_t    *surface,
>>  
>>  	    _cairo_xlib_shm_surface_get_ximage (&image->base, &shm_image);
>>  
>> +	    XSync (display->display, False);
>>  	    old_handler = XSetErrorHandler (_noop_error_handler);
> 
> I was thinking if only we could check for an error from this request,
> and remembered this is not xcb.
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

Even better: XSetErrorHandler() has no Display* argument. This sets a
global variable! This code is not even thread-safe and it cannot be.
Hopefully, no one uses multiple Displays in a single program...

Uli