code: final public void decrement(long decVal) {
          if (enabled) { // synchronize the update of lastValue
              lastSampleTime = updateIntegral();
              synchronized (this) {
                  current -= decVal;
              }
              updateWaterMark();
          } else {
              current -= decVal;
          }
      }
docs: /*
  Synchronizable: counter is "updated" with the input value