title: async uses a threadpool?
body: <p>I am new to C++ and I tried using std::async with launch::async to spawn new threads to handle incoming UDP packets. For every new request on a particular port, async spawns a new thread to handle it. </p>
  
  <p>Under load, I find that the udp packets were reaching me but it takes more than 10 seconds for async to spawn a thread and start processing the information. I was wondering if there is an underlying threadpool and that is the reason, async is blocked and is waiting. If yes, how can I increase the size of this thread pool?</p>