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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.hbase.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.wal.WAL.Reader;
28  import org.apache.hadoop.hbase.wal.WAL.Entry;
29  import org.apache.hadoop.hbase.wal.WALFactory;
30  
31  import java.io.IOException;
32  
33  /**
34   * Wrapper class around WAL to help manage the implementation details
35   * such as compression.
36   */
37  @InterfaceAudience.Private
38  public class ReplicationWALReaderManager {
39  
40    private static final Log LOG = LogFactory.getLog(ReplicationWALReaderManager.class);
41    private final FileSystem fs;
42    private final Configuration conf;
43    private long position = 0;
44    private Reader reader;
45    private Path lastPath;
46  
47    /**
48     * Creates the helper but doesn't open any file
49     * Use setInitialPosition after using the constructor if some content needs to be skipped
50     * @param fs
51     * @param conf
52     */
53    public ReplicationWALReaderManager(FileSystem fs, Configuration conf) {
54      this.fs = fs;
55      this.conf = conf;
56    }
57  
58    /**
59     * Opens the file at the current position
60     * @param path
61     * @return an WAL reader.
62     * @throws IOException
63     */
64    public Reader openReader(Path path) throws IOException {
65      // Detect if this is a new file, if so get a new reader else
66      // reset the current reader so that we see the new data
67      if (this.reader == null || !this.lastPath.equals(path)) {
68        this.closeReader();
69        this.reader = WALFactory.createReader(this.fs, path, this.conf);
70        this.lastPath = path;
71      } else {
72        try {
73          this.reader.reset();
74        } catch (NullPointerException npe) {
75          throw new IOException("NPE resetting reader, likely HDFS-4380", npe);
76        }
77      }
78      return this.reader;
79    }
80  
81    /**
82     * Get the next entry, returned and also added in the array
83     * @return a new entry or null
84     * @throws IOException
85     */
86    public Entry readNextAndSetPosition() throws IOException {
87      Entry entry = this.reader.next();
88      // Store the position so that in the future the reader can start
89      // reading from here. If the above call to next() throws an
90      // exception, the position won't be changed and retry will happen
91      // from the last known good position
92      this.position = this.reader.getPosition();
93      // We need to set the CC to null else it will be compressed when sent to the sink
94      if (entry != null) {
95        entry.setCompressionContext(null);
96      }
97      return entry;
98    }
99  
100   /**
101    * Advance the reader to the current position
102    * @throws IOException
103    */
104   public void seek() throws IOException {
105     if (this.position != 0) {
106       this.reader.seek(this.position);
107     }
108   }
109 
110   /**
111    * Get the position that we stopped reading at
112    * @return current position, cannot be negative
113    */
114   public long getPosition() {
115     return this.position;
116   }
117 
118   public void setPosition(long pos) {
119     this.position = pos;
120   }
121 
122   /**
123    * Close the current reader
124    * @throws IOException
125    */
126   public void closeReader() throws IOException {
127     if (this.reader != null) {
128       this.reader.close();
129       this.reader = null;
130     }
131   }
132 
133   /**
134    * Tell the helper to reset internal state
135    */
136   void finishCurrentFile() {
137     this.position = 0;
138     try {
139       this.closeReader();
140     } catch (IOException e) {
141       LOG.warn("Unable to close reader", e);
142     }
143   }
144 
145 }