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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.lang3.concurrent;
18  
19  /**
20   * <p>
21   * Definition of an interface for the thread-safe initialization of objects.
22   * </p>
23   * <p>
24   * The idea behind this interface is to provide access to an object in a
25   * thread-safe manner. A {@code ConcurrentInitializer} can be passed to multiple
26   * threads which can all access the object produced by the initializer. Through
27   * the {@link #get()} method the object can be queried.
28   * </p>
29   * <p>
30   * Concrete implementations of this interface will use different strategies for
31   * the creation of the managed object, e.g. lazy initialization or
32   * initialization in a background thread. This is completely transparent to
33   * client code, so it is possible to change the initialization strategy without
34   * affecting clients.
35   * </p>
36   *
37   * @since 3.0
38   * @version $Id: ConcurrentInitializer.java 1088899 2011-04-05 05:31:27Z bayard $
39   * @param <T> the type of the object managed by this initializer class
40   */
41  public interface ConcurrentInitializer<T> {
42      /**
43       * Returns the fully initialized object produced by this {@code
44       * ConcurrentInitializer}. A concrete implementation here returns the
45       * results of the initialization process. This method may block until
46       * results are available. Typically, once created the result object is
47       * always the same.
48       *
49       * @return the object created by this {@code ConcurrentException}
50       * @throws ConcurrentException if an error occurred during initialization of
51       * the object
52       */
53      T get() throws ConcurrentException;
54  }