001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.lang3.concurrent;
018
019/**
020 * Definition of an interface for the thread-safe initialization of objects.
021 *
022 * <p>
023 * The idea behind this interface is to provide access to an object in a
024 * thread-safe manner. A {@link ConcurrentInitializer} can be passed to multiple
025 * threads which can all access the object produced by the initializer. Through
026 * the {@link #get()} method the object can be queried.
027 * </p>
028 * <p>
029 * Concrete implementations of this interface will use different strategies for
030 * the creation of the managed object, e.g. lazy initialization or
031 * initialization in a background thread. This is completely transparent to
032 * client code, so it is possible to change the initialization strategy without
033 * affecting clients.
034 * </p>
035 *
036 * @since 3.0
037 * @param <T> the type of the object managed by this initializer class
038 */
039public interface ConcurrentInitializer<T> {
040    /**
041     * Returns the fully initialized object produced by this {@code
042     * ConcurrentInitializer}. A concrete implementation here returns the
043     * results of the initialization process. This method may block until
044     * results are available. Typically, once created the result object is
045     * always the same.
046     *
047     * @return the object created by this {@link ConcurrentException}
048     * @throws ConcurrentException if an error occurred during initialization of
049     * the object
050     */
051    T get() throws ConcurrentException;
052}