/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hive.ql.lib;
import org.apache.hadoop.hive.ql.parse.SemanticException;
/**
* Graph walker this class takes list of starting nodes and walks them in pre-order.
* If a rule fires up against a given node, we do not try to apply the rule
* on its children.
*/
public class PreOrderOnceWalker extends PreOrderWalker {
public PreOrderOnceWalker(Dispatcher disp) {
super(disp);
}
/**
* Walk the current operator and its descendants.
*
* @param nd
* current operator in the graph
* @throws SemanticException
*/
@Override
public void walk(Node nd) throws SemanticException {
opStack.push(nd);
dispatch(nd, opStack);
// The rule has been applied, we bail out
if (retMap.get(nd) != null) {
opStack.pop();
return;
}
// move all the children to the front of queue
if (nd.getChildren() != null) {
for (Node n : nd.getChildren()) {
walk(n);
}
}
opStack.pop();
}
}