org.apache.pig.impl.plan.DepthFirstWalker Maven / Gradle / Ivy
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* distributed with this work for additional information
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* 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,
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* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.pig.impl.plan;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import org.apache.pig.impl.util.Utils;
/**
* DepthFirstWalker traverses a plan in a depth first manner. One important note
* is that, in compliance with the PlanWalker contract, it only visits each node in
* the graph once.
*/
public class DepthFirstWalker >
extends PlanWalker {
/**
* @param plan Plan for this walker to traverse.
*/
public DepthFirstWalker(P plan) {
super(plan);
}
/**
* Begin traversing the graph.
* @param visitor Visitor this walker is being used by.
* @throws VisitorException if an error is encountered while walking.
*/
public void walk(PlanVisitor visitor) throws VisitorException {
List roots = mPlan.getRoots();
Set seen = new HashSet();
depthFirst(null, roots, seen, visitor);
}
public PlanWalker spawnChildWalker(P plan) {
return new DepthFirstWalker(plan);
}
// Suppress "unchecked" warnings for all logical plan related classes. Will revisit in logical plan rework
@SuppressWarnings("unchecked")
private void depthFirst(O node,
Collection successors,
Set seen,
PlanVisitor visitor) throws VisitorException {
if (successors == null) return;
for (O suc : successors) {
if (seen.add(suc)) {
suc.visit(visitor);
Collection newSuccessors = Utils.mergeCollection(mPlan.getSuccessors(suc), mPlan.getSoftLinkSuccessors(suc));
depthFirst(suc, newSuccessors, seen, visitor);
}
}
}
}