title: how to close a serialport used by another program
body: <p>I'm writting a SerialPort program. Sometimes when I want to open the SerialPort, an UnauthorizedAccessException is thrown :access to COM1 is denied. This is beause another program( which is written by someone else and I don't have its soucecode ) is using COM1, and that program doesn't close COM1 when it exits.
  I want to ask 2 questions:<br/></p>
  
  <ol>
  <li>How to close COM1  with my code (especially C# code) when it is used
  by another program?</li>
  <li>If I cannot close COM1 with C# code, how can I close or free COM1 in Windows OS?</li>
  </ol>
  
  <p>Thanks.</p>