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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.hadoop.chukwa.datacollection.writer;
20  
21  
22  import java.util.List;
23  import java.util.ArrayList;
24  import org.apache.hadoop.chukwa.Chunk;
25  import org.apache.hadoop.conf.Configuration;
26  
27  public interface ChukwaWriter {
28    
29    public static abstract class CommitStatus {}
30    
31    public static final CommitStatus COMMIT_OK = new CommitStatus() {};
32    public static final CommitStatus COMMIT_FAIL = new CommitStatus() {};
33    
34    /**
35     * COMMIT_PENDING should be returned if a writer has written data, but
36     * this data may ultimately disappear. Contains a list of strings, format
37     * unspecified, that agents can use to find out, eventually, if their data 
38     * has committed.  String <n> corresponds to the nth chunk passed to add().
39     * 
40     *  At present, the format is <sinkfilename> <offset>, 
41     *  where sinkfilename is the name of a sinkfile, without directory but with
42     *  .done suffix, and offset is the last byte of the associated chunk.
43     */
44    public static class COMMIT_PENDING extends CommitStatus {
45      public List<String> pendingEntries;
46    
47      public COMMIT_PENDING(int entries) {
48        pendingEntries = new ArrayList<String>(entries);
49      }
50      
51      public void addPend(String currentFileName, long dataSize) {
52        pendingEntries.add(currentFileName+ " " + dataSize+"\n");
53      }
54    }
55    
56    /**
57     * Called once to initialize this writer.
58     * 
59     * @param c
60     * @throws WriterException
61     */
62    public void init(Configuration c) throws WriterException;
63  
64    /**
65     * Called repeatedly with data that should be serialized.
66     * 
67     * Subclasses may assume that init() will be called before any calls to
68     * add(), and that add() won't be called after close().
69     * 
70     * @param chunks
71     * @return
72     * @throws WriterException
73     */
74    public CommitStatus add(List<Chunk> chunks) throws WriterException;
75  
76    /**
77     * Called once, indicating that the writer should close files and prepare
78     * to exit.
79     * @throws WriterException
80     */
81    public void close() throws WriterException;
82  
83  }