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.logging.log4j.core.async; 018 019import org.apache.logging.log4j.Level; 020 021/** 022 * Policy for deciding whether to discard the event, enqueue it or log the event on the current thread when the queue 023 * is full. 024 * <p> 025 * The asynchronous logging queue may become full when the application is logging faster than the underlying appender 026 * can keep up with for a long enough time to fill up the bounded queue. When this happens, the logging subsystem has to 027 * choose what to do with the event: 028 * </p> 029 * <ul> 030 * <li>Enqueue the event. This will block until the background thread removes a log event from the queue and space for 031 * new events becomes available in the queue. There is a risk of causing deadlock here when the new logging call was 032 * made while processing another logging call, for example when Log4j calls {@code toString()} on a message 033 * parameter, and the parameter object makes a logging call from its {@code toString()} method.</li> 034 * <li>Bypass the queue and send the event directly to the underlying appenders. This is the default policy used by 035 * Log4j since 2.7: see {@link DefaultAsyncQueueFullPolicy}. The benefit of this approach is that 036 * events will not get lost, but the disadvantage is that the resulting log file will be confusing for users, 037 * since log events will appear in the log file in random order: new events that are directly logged are followed 038 * by older log events taken from the queue.</li> 039 * <li>Discard the event. Log4j offers a variation of this policy where log events that are more verbose than 040 * a certain threshold are discarded, and other events are sent to the underlying appenders. 041 * See {@link DiscardingAsyncQueueFullPolicy} for details.</li> 042 * </ul> 043 * <p> 044 * See {@link AsyncQueueFullPolicyFactory} for how to install a custom policy. 045 * </p> 046 * 047 * @see AsyncQueueFullPolicyFactory 048 * @since 2.6 049 */ 050public interface AsyncQueueFullPolicy { 051 052 /** 053 * Returns the appropriate route for the current log event, given the specified parameters. 054 * 055 * @param backgroundThreadId the thread ID of the background thread. Can be compared with the current thread's ID. 056 * @param level the level of the log event 057 * @return the appropriate route for the current event 058 */ 059 EventRoute getRoute(final long backgroundThreadId, final Level level); 060}