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ByteStructVertexIdMessageBytesIterator xref
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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  
19  package org.apache.giraph.utils;
20  
21  import org.apache.hadoop.io.Writable;
22  import org.apache.hadoop.io.WritableComparable;
23  
24  import java.io.IOException;
25  import javax.annotation.concurrent.NotThreadSafe;
26  
27  /**
28   * Special iterator that reuses vertex ids and messages bytes so that the
29   * lifetime of the object is only until next() is called.
30   *
31   * Vertex id ownership can be released if desired through
32   * releaseCurrentVertexId().  This optimization allows us to cut down
33   * on the number of objects instantiated and garbage collected.  Messages
34   * can only be copied to an ExtendedDataOutput object
35   *
36   * @param <I> vertexId type parameter
37   * @param <M> message type parameter
38   */
39  @NotThreadSafe
40  public abstract class ByteStructVertexIdMessageBytesIterator<I
41    extends WritableComparable, M extends Writable>
42    extends ByteStructVertexIdDataIterator<I, M>
43    implements VertexIdMessageBytesIterator<I, M> {
44    /** Last message offset */
45    protected int messageOffset = -1;
46    /** Number of bytes in the last message */
47    protected int messageBytes = -1;
48  
49    /**
50     * Constructor with vertexIdData
51     *
52     * @param vertexIdData vertexIdData
53     */
54    public ByteStructVertexIdMessageBytesIterator(
55      AbstractVertexIdData<I, M> vertexIdData) {
56      super(vertexIdData);
57    }
58  
59    /**
60     * Moves to the next element in the iteration.
61     */
62    @Override
63    public void next() {
64      if (vertexId == null) {
65        vertexId = vertexIdData.getConf().createVertexId();
66      }
67  
68      try {
69        vertexId.readFields(extendedDataInput);
70        messageBytes = extendedDataInput.readInt();
71        messageOffset = extendedDataInput.getPos();
72        if (extendedDataInput.skipBytes(messageBytes) != messageBytes) {
73          throw new IllegalStateException("next: Failed to skip " +
74              messageBytes);
75        }
76      } catch (IOException e) {
77        throw new IllegalStateException("next: IOException", e);
78      }
79    }
80  }