code: @Trivial
      @Override
      public synchronized void reportCircuitHalfOpen() {
          if (circuitBreakerState != CircuitBreakerState.HALF_OPEN) {
              recordEndOfCircuitBreakerState(circuitBreakerState);
              circuitBreakerState = CircuitBreakerState.HALF_OPEN;
          }
      }
docs: {@inheritDoc}