    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
    019import org.apache.commons.lang3.function.FailableSupplier;
    020
    021/**
    022 * Defines the thread-safe initialization of objects.
    023 * <p>
    024 * 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
    025 * which can all access the object produced by the initializer. Through the {@link #get()} method the object can be queried.
    026 * </p>
    027 * <p>
    028 * Concrete implementations of this interface will use different strategies for the creation of the managed object, e.g. lazy initialization or initialization
    029 * in a background thread. This is completely transparent to client code, so it is possible to change the initialization strategy without affecting clients.
    030 * </p>
    031 * <p>
    032 * An implementation of {@link #get()} returns the fully initialized object produced by this {@code
    033 * ConcurrentInitializer}. A concrete implementation here returns the results of the initialization process. This method may block until results are available.
    034 * Typically, once created the result object is always the same.
    035 * </p>
    036 * <p>
    037 * An implementation throws {@link ConcurrentException} if an error occurred during initialization of the object.
    038 * </p>
    039 *
    040 * @since 3.0
    041 * @param <T> the type of the object managed by this initializer class.
    042 */
    043public interface ConcurrentInitializer<T> extends FailableSupplier<T, ConcurrentException> {
    044    // empty
    045}