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
018package org.apache.logging.log4j.core.util;
019
020import org.apache.logging.log4j.Marker;
021import 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 */
030public 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}