11.2 Handling the Output Buffer
The output buffer is an area used by Xlib to store requests.
The functions described in this section flush the output buffer
if the function would block or not return an event.
That is, all requests residing in the output buffer that
have not yet been sent are transmitted to the X server.
These functions differ in the additional tasks they might perform.
To flush the output buffer, use
XFlush().
To flush the output buffer and then wait until all requests have been processed,
use
XSync().
Christophe Tronche, ch@tronche.com