title: How to get the number of goroutines associated with a WaitGroup?
body: <p>Let’s say I use a <code>WaitGroup</code> to make the main thread of an application wait until all the goroutines I have launched from said main have completed.</p>
  <p>Is there a safe, straightforward, way to assess at any point in time how many goroutines associated with said <code>WaitGroup</code> are still running?</p>