org.apache.pig.newplan.ReverseDependencyOrderWalkerWOSeenChk Maven / Gradle / Ivy
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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.newplan;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import org.apache.pig.impl.logicalLayer.FrontendException;
import org.apache.pig.impl.util.Utils;
/**
* Visit a plan in the reverse of the dependency order. That is, every node
* after every node that depends on it is visited. Thus this is equivalent to
* doing a reverse topilogical sort on the graph and then visiting it in order.
*/
public class ReverseDependencyOrderWalkerWOSeenChk extends PlanWalker {
public ReverseDependencyOrderWalkerWOSeenChk(OperatorPlan plan) {
super(plan);
}
@Override
public PlanWalker spawnChildWalker(OperatorPlan plan) {
return new ReverseDependencyOrderWalker(plan);
}
/**
* Begin traversing the graph.
* @param visitor Visitor this walker is being used by.
* @throws VisitorException if an error is encountered while walking.
*/
@Override
public void walk(PlanVisitor visitor) throws FrontendException {
// This is highly inefficient, but our graphs are small so it should be okay.
// The algorithm works by starting at any node in the graph, finding it's
// successors and calling itself for each of those successors. When it
// finds a node that has no unfinished successors it puts that node in the
// list. It then unwinds itself putting each of the other nodes in the list.
// It keeps track of what nodes it's seen as it goes so it doesn't put any
// nodes in the graph twice.
List fifo = new ArrayList();
List roots = plan.getSources();
if (roots == null) return;
for (Operator op : roots) {
doAllSuccessors(op, fifo);
}
for (Operator op: fifo) {
op.accept(visitor);
}
}
protected void doAllSuccessors(Operator node,
Collection fifo) throws FrontendException {
Collection succs = Utils.mergeCollection(plan.getSuccessors(node), plan.getSoftLinkSuccessors(node));
if (succs != null && succs.size() > 0) {
// Do all our successors before ourself
for (Operator op : succs) {
doAllSuccessors(op, fifo);
}
}
// Now do ourself
fifo.add(node);
}
}