title: how to send mach message to windowserver
body: <p>I want to use the <code>mach_msg</code> to send some mach message to windowserver.
  but I do not know the <code>msg.msgh_remote_port</code> of windowserver.</p>
  
  <p>where can i get the remote_port of windowserver,so that, i can call some function 
  such as <code>_XSetGlobalForceConfig</code> in the CoreGraphics.Framework</p>
  
  <p>thks</p>