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 package org.apache.hadoop.hdfs.server.common;
19 
20 import org.apache.hadoop.classification.InterfaceAudience;
21 import org.apache.hadoop.util.SequentialNumber;
22 
23 /****************************************************************
24  * A GenerationStamp is a Hadoop FS primitive, identified by a long.
25  ****************************************************************/
26 @InterfaceAudience.Private
27 public class GenerationStamp extends SequentialNumber {
28   /**
29    * The last reserved generation stamp.
30    */
31   public static final long LAST_RESERVED_STAMP = 1000L;
32 
33   /**
34    * Generation stamp of blocks that pre-date the introduction
35    * of a generation stamp.
36    */
37   public static final long GRANDFATHER_GENERATION_STAMP = 0;
38 
39   /**
40    * Create a new instance, initialized to {@link #LAST_RESERVED_STAMP}.
41    */
GenerationStamp()42   public GenerationStamp() {
43     super(LAST_RESERVED_STAMP);
44   }
45 }
46