title: Latch that can be incremented
body: <p>Does anyone know if there is any latch implementation that does the following:</p>
  
  <ul>
  <li>has a method to decrement the latch value, or wait if the value is zero</li>
  <li>has a method for waiting for the latch value to be zero</li>
  <li>has a method for adding a number to the latch's value</li>
  </ul>