org.apache.hadoop.hive.ql.lib.DefaultGraphWalker Maven / Gradle / Ivy
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* 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 java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.IdentityHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
import java.util.Set;
import java.util.Stack;
import org.apache.hadoop.hive.ql.parse.SemanticException;
/**
* base class for operator graph walker this class takes list of starting ops
* and walks them one by one. it maintains list of walked operators
* (dispatchedList) and a list of operators that are discovered but not yet
* dispatched
*/
public class DefaultGraphWalker implements GraphWalker {
/**
* opStack keeps the nodes that have been visited, but have not been
* dispatched yet
*/
protected final Stack opStack;
/**
* opQueue keeps the nodes in the order that the were dispatched.
* Then it is used to go through the processed nodes and store
* the results that the dispatcher has produced (if any)
*/
protected final Queue opQueue;
/**
* toWalk stores the starting nodes for the graph that needs to be
* traversed
*/
protected final List toWalk = new ArrayList();
protected final IdentityHashMap retMap = new IdentityHashMap();
protected final Dispatcher dispatcher;
/**
* Constructor.
*
* @param disp
* dispatcher to call for each op encountered
*/
public DefaultGraphWalker(Dispatcher disp) {
dispatcher = disp;
opStack = new Stack();
opQueue = new LinkedList();
}
/**
* @return the doneList
*/
protected Set getDispatchedList() {
return retMap.keySet();
}
/**
* Dispatch the current operator.
*
* @param nd
* node being walked
* @param ndStack
* stack of nodes encountered
* @throws SemanticException
*/
public void dispatch(Node nd, Stack ndStack) throws SemanticException {
dispatchAndReturn(nd, ndStack);
}
/**
* Returns dispatch result
*/
public T dispatchAndReturn(Node nd, Stack ndStack) throws SemanticException {
Object[] nodeOutputs = null;
if (nd.getChildren() != null) {
nodeOutputs = new Object[nd.getChildren().size()];
int i = 0;
for (Node child : nd.getChildren()) {
nodeOutputs[i++] = retMap.get(child);
}
}
Object retVal = dispatcher.dispatch(nd, ndStack, nodeOutputs);
retMap.put(nd, retVal);
return (T) retVal;
}
/**
* starting point for walking.
*
* @throws SemanticException
*/
public void startWalking(Collection startNodes,
HashMap nodeOutput) throws SemanticException {
toWalk.addAll(startNodes);
while (toWalk.size() > 0) {
Node nd = toWalk.remove(0);
walk(nd);
// Some walkers extending DefaultGraphWalker e.g. ForwardWalker
// do not use opQueue and rely uniquely in the toWalk structure,
// thus we store the results produced by the dispatcher here
// TODO: rewriting the logic of those walkers to use opQueue
if (nodeOutput != null && getDispatchedList().contains(nd)) {
nodeOutput.put(nd, retMap.get(nd));
}
}
// Store the results produced by the dispatcher
while (!opQueue.isEmpty()) {
Node node = opQueue.poll();
if (nodeOutput != null && getDispatchedList().contains(node)) {
nodeOutput.put(node, retMap.get(node));
}
}
}
/**
* walk the current operator and its descendants.
*
* @param nd
* current operator in the graph
* @throws SemanticException
*/
protected void walk(Node nd) throws SemanticException {
// Push the node in the stack
opStack.push(nd);
// While there are still nodes to dispatch...
while (!opStack.empty()) {
Node node = opStack.peek();
if (node.getChildren() == null ||
getDispatchedList().containsAll(node.getChildren())) {
// Dispatch current node
if (!getDispatchedList().contains(node)) {
dispatch(node, opStack);
opQueue.add(node);
}
opStack.pop();
continue;
}
// Add a single child and restart the loop
for (Node childNode : node.getChildren()) {
if (!getDispatchedList().contains(childNode)) {
opStack.push(childNode);
break;
}
}
} // end while
}
}