title: PostThreadMessage to another process
body: <p>I want to post a message to a thread that is running as another process (in particular as a windows service). I've read the documentation for <a href="http://msdn.microsoft.com/en-us/library/ms644946%28VS.85%29.aspx" rel="nofollow noreferrer">PostThreadMessage</a> but there are some things unclear for me.</p>
  
  <p>How do I get a handle for my service's thread?</p>
  
  <blockquote>
    <p>The system only does marshalling for system messages (those in the range 0 to (WM_USER-1)). To send other messages (those >= WM_USER) to another process, you must do custom marshalling.</p>
  </blockquote>
  
  <p>I want to send my own messages, so how do I do this marshalling?</p>