| /* |
| * 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.pig.impl.plan; |
| |
| import java.util.ArrayList; |
| import java.util.Collection; |
| import java.util.Collections; |
| import java.util.HashSet; |
| import java.util.List; |
| import java.util.Set; |
| |
| import org.apache.pig.impl.util.Utils; |
| |
| |
| /** |
| * DependencyOrderWalker traverses the graph in such a way that no node is visited |
| * before all the nodes it depends on have been visited. Beyond this, it does not |
| * guarantee any particular order. So, you have a graph with node 1 2 3 4, and |
| * edges 1->3, 2->3, and 3->4, this walker guarnatees that 1 and 2 will be visited |
| * before 3 and 3 before 4, but it does not guarantee whether 1 or 2 will be |
| * visited first. |
| */ |
| public class DependencyOrderWalker <O extends Operator, P extends OperatorPlan<O>> |
| extends PlanWalker<O, P> { |
| |
| private final boolean walkLeavesInOrder; |
| |
| /** |
| * @param plan Plan for this walker to traverse. |
| */ |
| public DependencyOrderWalker(P plan) { |
| this(plan, false); |
| } |
| |
| /** |
| * @param plan Plan for this walker to traverse. |
| * @param boolean walkLeavesInOrder Sort the leaves before walking |
| */ |
| public DependencyOrderWalker(P plan, boolean walkLeavesInOrder) { |
| super(plan); |
| this.walkLeavesInOrder = walkLeavesInOrder; |
| } |
| |
| |
| /** |
| * Begin traversing the graph. |
| * @param visitor Visitor this walker is being used by. |
| * @throws VisitorException if an error is encountered while walking. |
| */ |
| @Override |
| @SuppressWarnings("unchecked") |
| public void walk(PlanVisitor<O, P> visitor) throws VisitorException { |
| // 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 |
| // predecessors and calling itself for each of those predecessors. When it |
| // finds a node that has no unfinished predecessors 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<O> fifo = new ArrayList<O>(); |
| Set<O> seen = new HashSet<O>(); |
| List<O> leaves = mPlan.getLeaves(); |
| if (leaves == null) return; |
| if (walkLeavesInOrder) { |
| Collections.sort(leaves); |
| } |
| for (O op : leaves) { |
| doAllPredecessors(op, seen, fifo); |
| } |
| for (O op: fifo) { |
| op.visit(visitor); |
| } |
| } |
| |
| @Override |
| public PlanWalker<O, P> spawnChildWalker(P plan) { |
| return new DependencyOrderWalker<O, P>(plan, walkLeavesInOrder); |
| } |
| |
| protected void doAllPredecessors(O node, |
| Set<O> seen, |
| Collection<O> fifo) throws VisitorException { |
| if (!seen.contains(node)) { |
| // We haven't seen this one before. |
| Collection<O> preds = Utils.mergeCollection(mPlan.getPredecessors(node), mPlan.getSoftLinkPredecessors(node)); |
| if (preds != null && preds.size() > 0) { |
| // Do all our predecessors before ourself |
| for (O op : preds) { |
| doAllPredecessors(op, seen, fifo); |
| } |
| } |
| // Now do ourself |
| seen.add(node); |
| fifo.add(node); |
| } |
| } |
| } |