    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}