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 * <p>
021 * Definition of an interface for the thread-safe initialization of objects.
022 * </p>
023 * <p>
024 * The idea behind this interface is to provide access to an object in a
025 * thread-safe manner. A {@code ConcurrentInitializer} can be passed to multiple
026 * threads which can all access the object produced by the initializer. Through
027 * the {@link #get()} method the object can be queried.
028 * </p>
029 * <p>
030 * Concrete implementations of this interface will use different strategies for
031 * the creation of the managed object, e.g. lazy initialization or
032 * initialization in a background thread. This is completely transparent to
033 * client code, so it is possible to change the initialization strategy without
034 * affecting clients.
035 * </p>
036 *
037 * @since 3.0
038 * @param <T> the type of the object managed by this initializer class
039 */
040public interface ConcurrentInitializer<T> {
041    /**
042     * Returns the fully initialized object produced by this {@code
043     * ConcurrentInitializer}. A concrete implementation here returns the
044     * results of the initialization process. This method may block until
045     * results are available. Typically, once created the result object is
046     * always the same.
047     *
048     * @return the object created by this {@code ConcurrentException}
049     * @throws ConcurrentException if an error occurred during initialization of
050     * the object
051     */
052    T get() throws ConcurrentException;
053}