title: how to quit the blocking of xlib's XNextEvent
body: <p>Under windows, the GUI thread usually call GetMessage to waiting for message,
  when another thread use PoseMessage put a message into the queue, then the
  GUI thread will return GetMessage (quit blocking).</p>
  
  <p>Does anyone can tell me, when I use XNextEvent under XWindows to waiting for
  event, how can I "wakeup" the GUI thread in another thread. Is there some
  API like PoseMessage I can use ?.</p>