title: How to check if stopCluster (R) worked
body: <p>When I try to remove a cluster from my workspace with stopCluster, it does not seem to work.  Below is the code I am using.</p>
  
  <pre><code>&gt; cl &lt;- makeCluster(3)
  &gt; cl
  socket cluster with 3 nodes on host ‘localhost’
  &gt; stopCluster(cl)
  &gt; cl
  socket cluster with 3 nodes on host ‘localhost’
  </code></pre>
  
  <p>Note that the command <code>cl</code> still is called a socket cluster with 3 nodes after I have supposedly removed it. Shouldn't I get an error that <code>object cl is not found</code>?  How do I know that my cluster has actually been removed?  A related question: if I close R, is the cluster terminated and my computer returned to its normal state of being able to use all of its cores? </p>