@SuppressWarnings("squid:S1452")
  default ListenableFuture<?> isBlocked() {
    return NOT_BLOCKED;
  }
Returns a future that will be completed when the operator becomes unblocked. If the operator is
not blocked, this method should return {@code NOT_BLOCKED}.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/Operator.java