protected void cloneConf() {
    if (!clonedConf) {
      clonedConf = true;
      conf = new HiveConf(conf);
    }
  }
Subscribe the feed of publisher. To prevent cycles, a task can only subscribe to its ancestor.
Feed is a generic form of execution-time feedback (type, value) pair from one task to another
task. Examples include dynamic partitions (which are only available at execution time). The
MoveTask may pass the list of dynamic partitions to the StatsTask since after the MoveTask the
list of dynamic partitions are lost (MoveTask moves them to the table's destination directory
which is mixed with old partitions).

@param publisher
         this feed provider.
ql/src/java/org/apache/hadoop/hive/ql/exec/Task.java