docs: public AsyncFuture getFutureFromIndex(int theIndex) {
          if (theIndex == READ_FUTURE_INDEX || theIndex == SYNC_READ_FUTURE_INDEX) {
              return this.readFuture;
          }
          if (theIndex == WRITE_FUTURE_INDEX || theIndex == SYNC_WRITE_FUTURE_INDEX) {
              return this.writeFuture;
          }
          return null;
      }