<p> This method may contain an instance of double-checked locking.&nbsp;
  This idiom is not correct according to the semantics of the Java memory
  model.&nbsp; For more information, see the web page
  <a href="http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html"
  >http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html</a>.</p>