docs: private void warnIfSuspiciousDoubleCompletion(Object s0, Object s1) {
          if (s0 != s1 && !(s0 instanceof CancellationException) && !(s1 instanceof CancellationException)) {
              logger.warning(String.format("Future.complete(Object) on completed future. "
                              + "Request: %s, current value: %s, offered value: %s",
                      invocationToString(), s0, s1));
          }
      }