View Javadoc

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.hbase.client;
19  
20  import java.io.IOException;
21  
22  import org.apache.hadoop.hbase.classification.InterfaceAudience;
23  
24  /**
25   * This class is designed to fit into the RetryingCaller class which forms the
26   * central piece of intelligence for the client side retries for most calls.
27   * 
28   * One can extend this class and intercept the RetryingCaller and add additional
29   * logic into the execution of a simple HTable operations like get, delete etc.
30   * 
31   * Concrete implementations of this calls are supposed to the thread safe. The
32   * object is used across threads to identify the fast failing threads.
33   * 
34   * For a concrete use case see {@link PreemptiveFastFailInterceptor}
35   * 
36   * Example use case : 
37   * try {
38   *   interceptor.intercept
39   *   doAction()
40   * } catch (Exception e) {
41   *   interceptor.handleFailure
42   * } finally {
43   *   interceptor.updateFaulireInfo
44   * }
45   * 
46   * The {@link RetryingCallerInterceptor} also acts as a factory
47   * for getting a new {@link RetryingCallerInterceptorContext}.
48   * 
49   */
50  
51  @InterfaceAudience.Private
52  abstract class RetryingCallerInterceptor {
53  
54    protected RetryingCallerInterceptor() {
55      // Empty constructor protected for NoOpRetryableCallerInterceptor
56    }
57  
58    /**
59     * This returns the context object for the current call.
60     * 
61     * @return context : the context that needs to be used during this call.
62     */
63    public abstract RetryingCallerInterceptorContext createEmptyContext();
64  
65    /**
66     * Call this function in case we caught a failure during retries.
67     * 
68     * @param context
69     *          : The context object that we obtained previously.
70     * @param t
71     *          : The exception that we caught in this particular try
72     * @throws IOException
73     */
74    public abstract void handleFailure(RetryingCallerInterceptorContext context,
75        Throwable t) throws IOException;
76  
77    /**
78     * Call this function alongside the actual call done on the callable.
79     * 
80     * @param abstractRetryingCallerInterceptorContext
81     * @throws PreemptiveFastFailException
82     */
83    public abstract void intercept(
84        RetryingCallerInterceptorContext abstractRetryingCallerInterceptorContext)
85        throws IOException;
86  
87    /**
88     * Call this function to update at the end of the retry. This is not necessary
89     * to happen.
90     * 
91     * @param context
92     */
93    public abstract void updateFailureInfo(
94        RetryingCallerInterceptorContext context);
95  
96    @Override
97    public abstract String toString();
98  }