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    
018    package org.apache.logging.log4j.core.util;
019    
020    import org.apache.logging.log4j.Marker;
021    import org.apache.logging.log4j.MarkerManager;
022    
023    /**
024     * Registry used for Runnable shutdown callback instances. Due to differing requirements of how late in the JVM
025     * lifecycle Log4j should be shut down, this interface is provided for customizing how to register shutdown hook
026     * callbacks. Implementations may optionally implement {@link org.apache.logging.log4j.core.LifeCycle}.
027     *
028     * @since 2.1
029     */
030    public interface ShutdownCallbackRegistry {
031    
032        /**
033         * System property to set to choose the ShutdownCallbackRegistry.
034         */
035        String SHUTDOWN_CALLBACK_REGISTRY = "log4j.shutdownCallbackRegistry";
036    
037        /**
038         * System property to set to override the global ability to register shutdown hooks.
039         */
040        String SHUTDOWN_HOOK_ENABLED = "log4j.shutdownHookEnabled";
041    
042        /**
043         * Shared Marker to indicate log messages corresponding to shutdown hooks.
044         */
045        Marker SHUTDOWN_HOOK_MARKER = MarkerManager.getMarker("SHUTDOWN HOOK");
046    
047        /**
048         * Adds a Runnable shutdown callback to this class.
049         *
050         * @param callback the shutdown callback to be executed upon shutdown.
051         * @return a Cancellable wrapper of the provided callback or {@code null} if the shutdown hook is disabled and
052         * cannot be added.
053         * @since 2.1
054         */
055        Cancellable addShutdownCallback(Runnable callback);
056    }