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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.hbase.replication.regionserver;
20  
21  import org.apache.commons.logging.Log;
22  import org.apache.commons.logging.LogFactory;
23  import org.apache.hadoop.classification.InterfaceAudience;
24  import org.apache.hadoop.conf.Configuration;
25  import org.apache.hadoop.fs.FileSystem;
26  import org.apache.hadoop.fs.Path;
27  import org.apache.hadoop.hbase.regionserver.wal.HLog;
28  import org.apache.hadoop.hbase.regionserver.wal.HLogFactory;
29  
30  import java.io.IOException;
31  
32  /**
33   * Wrapper class around HLog to help manage the implementation details
34   * such as compression.
35   */
36  @InterfaceAudience.Private
37  public class ReplicationHLogReaderManager {
38  
39    private static final Log LOG = LogFactory.getLog(ReplicationHLogReaderManager.class);
40    private final FileSystem fs;
41    private final Configuration conf;
42    private long position = 0;
43    private HLog.Reader reader;
44    private Path lastPath;
45  
46    /**
47     * Creates the helper but doesn't open any file
48     * Use setInitialPosition after using the constructor if some content needs to be skipped
49     * @param fs
50     * @param conf
51     */
52    public ReplicationHLogReaderManager(FileSystem fs, Configuration conf) {
53      this.fs = fs;
54      this.conf = conf;
55    }
56  
57    /**
58     * Opens the file at the current position
59     * @param path
60     * @return an HLog reader.
61     * @throws IOException
62     */
63    public HLog.Reader openReader(Path path) throws IOException {
64      // Detect if this is a new file, if so get a new reader else
65      // reset the current reader so that we see the new data
66      if (this.reader == null || !this.lastPath.equals(path)) {
67        this.closeReader();
68        this.reader = HLogFactory.createReader(this.fs, path, this.conf);
69        this.lastPath = path;
70      } else {
71        this.reader.reset();
72      }
73      return this.reader;
74    }
75  
76    /**
77     * Get the next entry, returned and also added in the array
78     * @param entriesArray
79     * @param currentNbEntries
80     * @return a new entry or null
81     * @throws IOException
82     */
83    public HLog.Entry readNextAndSetPosition(HLog.Entry[] entriesArray,
84                                             int currentNbEntries) throws IOException {
85      HLog.Entry entry = this.reader.next(entriesArray[currentNbEntries]);
86      // Store the position so that in the future the reader can start
87      // reading from here. If the above call to next() throws an
88      // exception, the position won't be changed and retry will happen
89      // from the last known good position
90      this.position = this.reader.getPosition();
91      // We need to set the CC to null else it will be compressed when sent to the sink
92      if (entry != null) {
93        entry.setCompressionContext(null);
94      }
95      return entry;
96    }
97  
98    /**
99     * Advance the reader to the current position
100    * @throws IOException
101    */
102   public void seek() throws IOException {
103     if (this.position != 0) {
104       this.reader.seek(this.position);
105     }
106   }
107 
108   /**
109    * Get the position that we stopped reading at
110    * @return current position, cannot be negative
111    */
112   public long getPosition() {
113     return this.position;
114   }
115 
116   public void setPosition(long pos) {
117     this.position = pos;
118   }
119 
120   /**
121    * Close the current reader
122    * @throws IOException
123    */
124   public void closeReader() throws IOException {
125     if (this.reader != null) {
126       this.reader.close();
127       this.reader = null;
128     }
129   }
130 
131   /**
132    * Tell the helper to reset internal state
133    */
134   void finishCurrentFile() {
135     this.position = 0;
136     try {
137       this.closeReader();
138     } catch (IOException e) {
139       LOG.warn("Unable to close reader", e);
140     }
141   }
142 
143 }