code: synchronized List<FutureReadResultEntry> seal() {
          this.sealed = true;
          List<FutureReadResultEntry> result = new ArrayList<>(this.reads);
          this.reads.clear();
          return result;
      }
docs: Seals this PendingMerge instance and returns a list of all the registered FutureReadResultEntries associated with it.
  After this method returns, all calls to register() will return false.
  @return A List of all the registered FutureReadResultEntries recorded.