/**
* 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.parse;
import java.util.List;
import org.apache.hadoop.hive.ql.lib.DefaultGraphWalker;
import org.apache.hadoop.hive.ql.lib.Dispatcher;
import org.apache.hadoop.hive.ql.lib.Node;
/**
* Walks the operator tree in pre order fashion.
*/
public class GenMapRedWalker extends DefaultGraphWalker {
/**
* constructor of the walker - the dispatcher is passed.
*
* @param disp
* the dispatcher to be called for each node visited
*/
public GenMapRedWalker(Dispatcher disp) {
super(disp);
}
/**
* Walk the given operator.
*
* @param nd
* operator being walked
*/
@Override
protected void walk(Node nd) throws SemanticException {
List<? extends Node> children = nd.getChildren();
// maintain the stack of operators encountered
opStack.push(nd);
Boolean result = dispatchAndReturn(nd, opStack);
// kids of reduce sink operator or mapjoin operators merged into root task
// need not be traversed again
if (children == null || result == Boolean.FALSE) {
opStack.pop();
return;
}
// move all the children to the front of queue
for (Node ch : children) {
walk(ch);
}
// done with this operator
opStack.pop();
}
}