title: What happens when a thread pool is exhausted?
body: <p>In a recent course at school about networking / operating systems I learned about thread pools. Now he basic functionality is pretty straight forward and I understand this.</p>
  
  <p>However, what's not specified in my book is what happens when the thread pool is exhausted? For example you have a pool with 20 threads in it and you have 20 connected clients. Another client tries to connect but there's no threads left in the pool, what happens then? Does the client go in a queue? Does the system make another thread to put in the pool? Something else?</p>