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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  import org.apache.commons.lang3.function.FailableSupplier;
20  
21  /**
22   * Defines the thread-safe initialization of objects.
23   * <p>
24   * The idea behind this interface is to provide access to an object in a thread-safe manner. A {@link ConcurrentInitializer} can be passed to multiple threads
25   * which can all access the object produced by the initializer. Through the {@link #get()} method the object can be queried.
26   * </p>
27   * <p>
28   * Concrete implementations of this interface will use different strategies for the creation of the managed object, e.g. lazy initialization or initialization
29   * in a background thread. This is completely transparent to client code, so it is possible to change the initialization strategy without affecting clients.
30   * </p>
31   * <p>
32   * An implementation of {@link #get()} returns the fully initialized object produced by this {@code
33   * ConcurrentInitializer}. A concrete implementation here returns the results of the initialization process. This method may block until results are available.
34   * Typically, once created the result object is always the same.
35   * </p>
36   * <p>
37   * An implementation throws {@link ConcurrentException} if an error occurred during initialization of the object.
38   * </p>
39   *
40   * @since 3.0
41   * @param <T> the type of the object managed by this initializer class.
42   */
43  public interface ConcurrentInitializer<T> extends FailableSupplier<T, ConcurrentException> {
44      // empty
45  }