1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache license, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the license for the specific language governing permissions and
15 * limitations under the license.
16 */
17 package org.apache.logging.log4j.core.async;
18
19 import org.apache.logging.log4j.Level;
20
21 /**
22 * Policy for deciding whether to discard the event, enqueue it or log the event on the current thread when the queue
23 * is full.
24 * <p>
25 * The asynchronous logging queue may become full when the application is logging faster than the underlying appender
26 * can keep up with for a long enough time to fill up the bounded queue. When this happens, the logging subsystem has to
27 * choose what to do with the event:
28 * </p>
29 * <ul>
30 * <li>Enqueue the event. This will block until the background thread removes a log event from the queue and space for
31 * new events becomes available in the queue. There is a risk of causing deadlock here when the new logging call was
32 * made while processing another logging call, for example when Log4j calls {@code toString()} on a message
33 * parameter, and the parameter object makes a logging call from its {@code toString()} method.</li>
34 * <li>Bypass the queue and send the event directly to the underlying appenders. This is the default policy used by
35 * Log4j since 2.7: see {@link DefaultAsyncQueueFullPolicy}. The benefit of this approach is that
36 * events will not get lost, but the disadvantage is that the resulting log file will be confusing for users,
37 * since log events will appear in the log file in random order: new events that are directly logged are followed
38 * by older log events taken from the queue.</li>
39 * <li>Discard the event. Log4j offers a variation of this policy where log events that are more verbose than
40 * a certain threshold are discarded, and other events are sent to the underlying appenders.
41 * See {@link DiscardingAsyncQueueFullPolicy} for details.</li>
42 * </ul>
43 * <p>
44 * See {@link AsyncQueueFullPolicyFactory} for how to install a custom policy.
45 * </p>
46 *
47 * @see AsyncQueueFullPolicyFactory
48 * @since 2.6
49 */
50 public interface AsyncQueueFullPolicy {
51
52 /**
53 * Returns the appropriate route for the current log event, given the specified parameters.
54 *
55 * @param backgroundThreadId the thread ID of the background thread. Can be compared with the current thread's ID.
56 * @param level the level of the log event
57 * @return the appropriate route for the current event
58 */
59 EventRoute getRoute(final long backgroundThreadId, final Level level);
60 }