title: Racket not closing TCP port
body: <p>I've written a simple HTTP echo server in Racket. When I run the server from within DrRacket and then click the Stop button, my program terminates, but the port that was being used takes an annoyingly long time to close. If I run <code>lsof -i :&lt;port&gt;</code> in my terminal after terminating the program, I don't see anything bound to that port, but DrRacket disagrees and refuses to let me restart my program, telling me that something is already bound to that port.</p>
  
  <p>Is this a bug in Racket, or is there something that I'm missing?</p>