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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.comm.aggregators;
20  
21  import java.io.IOException;
22  import org.apache.giraph.utils.ExtendedByteArrayDataOutput;
23  import org.apache.giraph.utils.ExtendedDataOutput;
24  
25  /**
26   * Wrapper for output stream which keeps the place in the beginning for the
27   * count of objects which were written to it
28   */
29  public abstract class CountingOutputStream {
30    /** DataOutput to which subclasses will be writing data */
31    protected ExtendedDataOutput dataOutput;
32    /** Counter for objects which were written to the stream */
33    private int counter;
34  
35    /**
36     * Default constructor
37     */
38    public CountingOutputStream() {
39      dataOutput = new ExtendedByteArrayDataOutput();
40      reset();
41    }
42  
43    /**
44     * Subclasses should call this method when an object is written
45     */
46    protected void incrementCounter() {
47      counter++;
48    }
49  
50    /**
51     * Get the number of bytes in the stream
52     *
53     * @return Number of bytes
54     */
55    protected int getSize() {
56      return dataOutput.getPos();
57    }
58  
59    /**
60     * Returns all the data from the stream and clears it.
61     *
62     * @return Number of objects followed by the data written to the stream
63     */
64    public byte[] flush() {
65      dataOutput.writeInt(0, counter);
66      // Actual flush not required, this is a byte array
67      byte[] ret = dataOutput.toByteArray();
68      reset();
69      return ret;
70    }
71  
72    /**
73     * Reset the stream
74     */
75    private void reset() {
76      dataOutput.reset();
77      // reserve the place for count to be written in the end
78      try {
79        dataOutput.writeInt(0);
80      } catch (IOException e) {
81        throw new IllegalStateException("reset: Got IOException", e);
82      }
83      counter = 0;
84    }
85  }