title: Thread communication using SendMessage
body: <p>my question is : how can I use SendMessage() to implement thread communication between two threads, one with a window (GUI) and the other with no window?</p>
  
  <p>The problem is that SendMessage() needs a handle (HWND)?</p>
  
  <p>Another detail about my project : Two threads, one running managed code (the one with the user interface), and the other running native code (the one without window)</p>
  
  <p>Thank you very much!</p>