/***********************************************************************************************************************
* Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
*
* Licensed 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 eu.stratosphere.spargel.java;
import java.io.Serializable;
import java.util.Collection;
import java.util.Iterator;
import eu.stratosphere.api.common.aggregators.Aggregator;
import eu.stratosphere.api.common.functions.IterationRuntimeContext;
import eu.stratosphere.api.java.tuple.Tuple;
import eu.stratosphere.api.java.tuple.Tuple2;
import eu.stratosphere.api.java.tuple.Tuple3;
import eu.stratosphere.spargel.java.OutgoingEdge;
import eu.stratosphere.types.Value;
import eu.stratosphere.util.Collector;
/**
* The base class for functions that produce messages between vertices as a part of a {@link VertexCentricIteration}.
*
* @param <VertexKey> The type of the vertex key (the vertex identifier).
* @param <VertexValue> The type of the vertex value (the state of the vertex).
* @param <Message> The type of the message sent between vertices along the edges.
* @param <EdgeValue> The type of the values that are associated with the edges.
*/
public abstract class MessagingFunction<VertexKey extends Comparable<VertexKey>, VertexValue, Message, EdgeValue> implements Serializable {
private static final long serialVersionUID = 1L;
// --------------------------------------------------------------------------------------------
// Public API Methods
// --------------------------------------------------------------------------------------------
/**
* This method is invoked once per superstep for each vertex that was changed in that superstep.
* It needs to produce the messages that will be received by vertices in the next superstep.
*
* @param vertexKey The key of the vertex that was changed.
* @param vertexValue The value (state) of the vertex that was changed.
*
* @throws Exception The computation may throw exceptions, which causes the superstep to fail.
*/
public abstract void sendMessages(VertexKey vertexKey, VertexValue vertexValue) throws Exception;
/**
* This method is executed one per superstep before the vertex update function is invoked for each vertex.
*
* @throws Exception Exceptions in the pre-superstep phase cause the superstep to fail.
*/
public void preSuperstep() throws Exception {}
/**
* This method is executed one per superstep after the vertex update function has been invoked for each vertex.
*
* @throws Exception Exceptions in the post-superstep phase cause the superstep to fail.
*/
public void postSuperstep() throws Exception {}
/**
* Gets an {@link java.lang.Iterable} with all outgoing edges. This method is mutually exclusive with
* {@link #sendMessageToAllNeighbors(Object)} and may be called only once.
*
* @return An iterator with all outgoing edges.
*/
@SuppressWarnings("unchecked")
public Iterable<OutgoingEdge<VertexKey, EdgeValue>> getOutgoingEdges() {
if (edgesUsed) {
throw new IllegalStateException("Can use either 'getOutgoingEdges()' or 'sendMessageToAllTargets()' exactly once.");
}
edgesUsed = true;
if (this.edgeWithValueIter != null) {
this.edgeWithValueIter.set((Iterator<Tuple3<VertexKey, VertexKey, EdgeValue>>) edges);
return this.edgeWithValueIter;
} else {
this.edgeNoValueIter.set((Iterator<Tuple2<VertexKey, VertexKey>>) edges);
return this.edgeNoValueIter;
}
}
/**
* Sends the given message to all vertices that are targets of an outgoing edge of the changed vertex.
* This method is mutually exclusive to the method {@link #getOutgoingEdges()} and may be called only once.
*
* @param m The message to send.
*/
public void sendMessageToAllNeighbors(Message m) {
if (edgesUsed) {
throw new IllegalStateException("Can use either 'getOutgoingEdges()' or 'sendMessageToAllTargets()' exactly once.");
}
edgesUsed = true;
outValue.f1 = m;
while (edges.hasNext()) {
Tuple next = (Tuple) edges.next();
VertexKey k = next.getField(1);
outValue.f0 = k;
out.collect(outValue);
}
}
/**
* Sends the given message to the vertex identified by the given key. If the target vertex does not exist,
* the next superstep will cause an exception due to a non-deliverable message.
*
* @param target The key (id) of the target vertex to message.
* @param m The message.
*/
public void sendMessageTo(VertexKey target, Message m) {
outValue.f0 = target;
outValue.f1 = m;
out.collect(outValue);
}
// --------------------------------------------------------------------------------------------
/**
* Gets the number of the superstep, starting at <tt>1</tt>.
*
* @return The number of the current superstep.
*/
public int getSuperstepNumber() {
return this.runtimeContext.getSuperstepNumber();
}
/**
* Gets the iteration aggregator registered under the given name. The iteration aggregator is combines
* all aggregates globally once per superstep and makes them available in the next superstep.
*
* @param name The name of the aggregator.
* @return The aggregator registered under this name, or null, if no aggregator was registered.
*/
public <T extends Aggregator<?>> T getIterationAggregator(String name) {
return this.runtimeContext.<T>getIterationAggregator(name);
}
/**
* Get the aggregated value that an aggregator computed in the previous iteration.
*
* @param name The name of the aggregator.
* @return The aggregated value of the previous iteration.
*/
public <T extends Value> T getPreviousIterationAggregate(String name) {
return this.runtimeContext.<T>getPreviousIterationAggregate(name);
}
/**
* Gets the broadcast data set registered under the given name. Broadcast data sets
* are available on all parallel instances of a function. They can be registered via
* {@link VertexCentricIteration#addBroadcastSetForMessagingFunction(String, eu.stratosphere.api.java.DataSet)}.
*
* @param name The name under which the broadcast set is registered.
* @return The broadcast data set.
*/
public <T> Collection<T> getBroadcastSet(String name) {
return this.runtimeContext.<T>getBroadcastVariable(name);
}
// --------------------------------------------------------------------------------------------
// internal methods and state
// --------------------------------------------------------------------------------------------
private Tuple2<VertexKey, Message> outValue;
private IterationRuntimeContext runtimeContext;
private Iterator<?> edges;
private Collector<Tuple2<VertexKey, Message>> out;
private EdgesIteratorNoEdgeValue<VertexKey, EdgeValue> edgeNoValueIter;
private EdgesIteratorWithEdgeValue<VertexKey, EdgeValue> edgeWithValueIter;
private boolean edgesUsed;
void init(IterationRuntimeContext context, boolean hasEdgeValue) {
this.runtimeContext = context;
this.outValue = new Tuple2<VertexKey, Message>();
if (hasEdgeValue) {
this.edgeWithValueIter = new EdgesIteratorWithEdgeValue<VertexKey, EdgeValue>();
} else {
this.edgeNoValueIter = new EdgesIteratorNoEdgeValue<VertexKey, EdgeValue>();
}
}
void set(Iterator<?> edges, Collector<Tuple2<VertexKey, Message>> out) {
this.edges = edges;
this.out = out;
this.edgesUsed = false;
}
private static final class EdgesIteratorNoEdgeValue<VertexKey extends Comparable<VertexKey>, EdgeValue>
implements Iterator<OutgoingEdge<VertexKey, EdgeValue>>, Iterable<OutgoingEdge<VertexKey, EdgeValue>>
{
private Iterator<Tuple2<VertexKey, VertexKey>> input;
private OutgoingEdge<VertexKey, EdgeValue> edge = new OutgoingEdge<VertexKey, EdgeValue>();
void set(Iterator<Tuple2<VertexKey, VertexKey>> input) {
this.input = input;
}
@Override
public boolean hasNext() {
return input.hasNext();
}
@Override
public OutgoingEdge<VertexKey, EdgeValue> next() {
Tuple2<VertexKey, VertexKey> next = input.next();
edge.set(next.f1, null);
return edge;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
@Override
public Iterator<OutgoingEdge<VertexKey, EdgeValue>> iterator() {
return this;
}
}
private static final class EdgesIteratorWithEdgeValue<VertexKey extends Comparable<VertexKey>, EdgeValue>
implements Iterator<OutgoingEdge<VertexKey, EdgeValue>>, Iterable<OutgoingEdge<VertexKey, EdgeValue>>
{
private Iterator<Tuple3<VertexKey, VertexKey, EdgeValue>> input;
private OutgoingEdge<VertexKey, EdgeValue> edge = new OutgoingEdge<VertexKey, EdgeValue>();
void set(Iterator<Tuple3<VertexKey, VertexKey, EdgeValue>> input) {
this.input = input;
}
@Override
public boolean hasNext() {
return input.hasNext();
}
@Override
public OutgoingEdge<VertexKey, EdgeValue> next() {
Tuple3<VertexKey, VertexKey, EdgeValue> next = input.next();
edge.set(next.f1, next.f2);
return edge;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
@Override
public Iterator<OutgoingEdge<VertexKey, EdgeValue>> iterator() {
return this;
}
}
}