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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.ipc;
20  
21  import java.io.IOException;
22  import java.io.InterruptedIOException;
23  
24  import org.apache.hadoop.classification.InterfaceAudience;
25  
26  import com.google.protobuf.RpcCallback;
27  
28  /**
29   * Simple {@link RpcCallback} implementation providing a
30   * {@link java.util.concurrent.Future}-like {@link BlockingRpcCallback#get()} method, which
31   * will block util the instance's {@link BlockingRpcCallback#run(Object)} method has been called.
32   * {@code R} is the RPC response type that will be passed to the {@link #run(Object)} method.
33   */
34  @InterfaceAudience.Private
35  public class BlockingRpcCallback<R> implements RpcCallback<R> {
36    private R result;
37    private boolean resultSet = false;
38  
39    /**
40     * Called on completion of the RPC call with the response object, or {@code null} in the case of
41     * an error.
42     * @param parameter the response object or {@code null} if an error occurred
43     */
44    @Override
45    public void run(R parameter) {
46      synchronized (this) {
47        result = parameter;
48        resultSet = true;
49        this.notify();
50      }
51    }
52  
53    /**
54     * Returns the parameter passed to {@link #run(Object)} or {@code null} if a null value was
55     * passed.  When used asynchronously, this method will block until the {@link #run(Object)}
56     * method has been called.
57     * @return the response object or {@code null} if no response was passed
58     */
59    public synchronized R get() throws IOException {
60      while (!resultSet) {
61        try {
62          this.wait();
63        } catch (InterruptedException ie) {
64          InterruptedIOException exception = new InterruptedIOException(ie.getMessage());
65          exception.initCause(ie);
66          throw exception;
67        }
68      }
69      return result;
70    }
71  }