title: Lock file when opening, unlock it when closing it
body: <p>Is there a way to have ST check if a file is already opened by another user (on a Linux system) and if so not open the file and notify the user?</p>
  
  <p>I guess this involves ST locking the file upon opening it and unlocking it when the file is closed.</p>
  
  <p>Any ideas?</p>
  
  <p>Thank you.</p>