1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one 3 * or more contributor license agreements. See the NOTICE file 4 * distributed with this work for additional information 5 * regarding copyright ownership. The ASF licenses this file 6 * to you under the Apache License, Version 2.0 (the 7 * "License"); you may not use this file except in compliance 8 * with the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 package org.apache.giraph.types; 19 20 import java.io.DataInput; 21 import java.io.DataOutput; 22 import java.io.IOException; 23 24 import org.apache.hadoop.io.Writable; 25 26 /** 27 * Type marking that in a particular superstep there will not be 28 * sent messages. 29 * We cannot use NullWritable for this, as you could send NullWritable, 30 * to send a signal (whether a vertex receives a message or not) 31 */ 32 public class NoMessage implements Writable { 33 @Override 34 public void readFields(DataInput in) throws IOException { 35 throw new IllegalStateException("NoMessage should never be read"); 36 } 37 38 @Override 39 public void write(DataOutput out) throws IOException { 40 throw new IllegalStateException("NoMessage should never be written"); 41 } 42 }