private void cancelAsyncInitOps() {
    for (Future<?> f : asyncInitOperations) {
      f.cancel(true);
    }
    asyncInitOperations.clear();
  }
Initializes operators only if all parents have been initialized. Calls
operator specific initializer which then initializes child ops.

@param hconf
@param inputOIs
         input object inspector array indexes by tag id. null value is
         ignored.
@throws HiveException
ql/src/java/org/apache/hadoop/hive/ql/exec/Operator.java