code: public void invoke(Runnable r) throws Exception {
          try {
              r.run();
              succeed();
          } catch (Exception e) {
              fail();
              throw e;
          }
      }
docs: Wrap the given service call with the {@link RequestCounter}
  to count the number of calls made.
  @param r the {@link Runnable} to attempt
  
  @throws Exception if <code>c</code> throws one during
  execution