static boolean hasBranchFinished(Object... children) {
    for (Object child : children) {
      if (child == null) {
        return false;
      }
    }
    return true;
  }
Split two tasks by creating a temporary file between them.

@param op reduce sink operator being processed
@param parentTask the parent task
@param childTask the child task
@param opProcCtx context
ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMapRedUtils.java