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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  package org.apache.omid.tso;
19  
20  import java.io.IOException;
21  
22  /**
23   * Allows to reset the TSO state and register observers for being notified
24   * when changes occur
25   */
26  public interface TSOStateManager {
27  
28      /**
29       * Represents the state of the TSO
30       */
31      class TSOState {
32  
33          // TSO state variables
34          private final long lowWatermark;
35  
36          public TSOState(long lowWatermark, long epoch) {
37              this.lowWatermark = lowWatermark;
38          }
39  
40          public long getLowWatermark() {
41              return lowWatermark;
42          }
43  
44          public long getEpoch() {
45              // In this implementation the epoch == low watermark
46              return lowWatermark;
47          }
48  
49          @Override
50          public String toString() {
51              return String.format("LWM %d/Epoch %d", getLowWatermark(), getEpoch());
52          }
53  
54      }
55  
56      /**
57       * Allows implementors to receive the new state when changes occur
58       */
59      interface StateObserver {
60  
61          /**
62           * Notifies the observer about the change in state
63           * @param state
64           *            the new TSOState
65           * @throws InterruptedException
66           */
67          void update(TSOState state) throws Exception;
68  
69      }
70  
71      /**
72       * Allows to register observers for receiving state changes
73       *
74       * @param observer
75       *            the observer to register
76       */
77      void register(StateObserver observer);
78  
79      /**
80       * Allows to de-register observers for stopping receiving changes
81       *
82       * @param observer
83       *            the observer to unregister
84       */
85      void unregister(StateObserver observer);
86  
87      /**
88       * Allows to initialize the state
89       *
90       * @return the new state
91       * @throws IOException
92       *             when problems resetting occur
93       * @throws InterruptedException
94       */
95      TSOState initialize() throws Exception;
96  
97  }