code: protected void didInvokeUnit (Unit unit, long start)
      {
          // track some performance metrics
          if (PERF_TRACK) {
              long duration = System.currentTimeMillis() - start;
              Object key = unit.getClass();
              recordMetrics(key, duration);
  
              // report long runners
              long thresh = unit.getLongThreshold();
              if (thresh == 0) {
                  thresh = _longThreshold;
              }
              if (duration > thresh) {
                  StringBuilder msg = new StringBuilder();
                  msg.append((duration >= 10*thresh) ? "Really long" : "Long");
                  msg.append(" invoker unit [unit=").append(unit);
                  msg.append(" (").append(key).append("), time=").append(duration).append("ms");
                  if (unit.getDetail() != null) {
                      msg.append(", detail=").append(unit.getDetail());
                  }
                  log.warning(msg.append("].").toString());
              }
          }
      }
docs: Called before we process an invoker unit.
  
  @param unit the unit about to be invoked.
  @param start a timestamp recorded immediately before invocation if {@link #PERF_TRACK} is
  enabled, 0L otherwise.