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     */
017    package 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     * @version $Id: ConcurrentInitializer.java 1088899 2011-04-05 05:31:27Z bayard $
039     * @param <T> the type of the object managed by this initializer class
040     */
041    public interface ConcurrentInitializer<T> {
042        /**
043         * Returns the fully initialized object produced by this {@code
044         * ConcurrentInitializer}. A concrete implementation here returns the
045         * results of the initialization process. This method may block until
046         * results are available. Typically, once created the result object is
047         * always the same.
048         *
049         * @return the object created by this {@code ConcurrentException}
050         * @throws ConcurrentException if an error occurred during initialization of
051         * the object
052         */
053        T get() throws ConcurrentException;
054    }