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| <pre><span class="sourceLineNo">001</span>/*<a name="line.1"></a> |
| <span class="sourceLineNo">002</span> * Licensed to the Apache Software Foundation (ASF) under one or more<a name="line.2"></a> |
| <span class="sourceLineNo">003</span> * contributor license agreements. See the NOTICE file distributed with<a name="line.3"></a> |
| <span class="sourceLineNo">004</span> * this work for additional information regarding copyright ownership.<a name="line.4"></a> |
| <span class="sourceLineNo">005</span> * The ASF licenses this file to You under the Apache license, Version 2.0<a name="line.5"></a> |
| <span class="sourceLineNo">006</span> * (the "License"); you may not use this file except in compliance with<a name="line.6"></a> |
| <span class="sourceLineNo">007</span> * the License. You may obtain a copy of the License at<a name="line.7"></a> |
| <span class="sourceLineNo">008</span> *<a name="line.8"></a> |
| <span class="sourceLineNo">009</span> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.9"></a> |
| <span class="sourceLineNo">010</span> *<a name="line.10"></a> |
| <span class="sourceLineNo">011</span> * Unless required by applicable law or agreed to in writing, software<a name="line.11"></a> |
| <span class="sourceLineNo">012</span> * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.12"></a> |
| <span class="sourceLineNo">013</span> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.13"></a> |
| <span class="sourceLineNo">014</span> * See the license for the specific language governing permissions and<a name="line.14"></a> |
| <span class="sourceLineNo">015</span> * limitations under the license.<a name="line.15"></a> |
| <span class="sourceLineNo">016</span> */<a name="line.16"></a> |
| <span class="sourceLineNo">017</span>package org.apache.logging.log4j.message;<a name="line.17"></a> |
| <span class="sourceLineNo">018</span><a name="line.18"></a> |
| <span class="sourceLineNo">019</span>import java.lang.annotation.Documented;<a name="line.19"></a> |
| <span class="sourceLineNo">020</span>import java.lang.annotation.ElementType;<a name="line.20"></a> |
| <span class="sourceLineNo">021</span>import java.lang.annotation.Retention;<a name="line.21"></a> |
| <span class="sourceLineNo">022</span>import java.lang.annotation.RetentionPolicy;<a name="line.22"></a> |
| <span class="sourceLineNo">023</span>import java.lang.annotation.Target;<a name="line.23"></a> |
| <span class="sourceLineNo">024</span><a name="line.24"></a> |
| <span class="sourceLineNo">025</span>/**<a name="line.25"></a> |
| <span class="sourceLineNo">026</span> * Annotation that signals to asynchronous logging components that messages of this type can safely be passed to<a name="line.26"></a> |
| <span class="sourceLineNo">027</span> * a background thread without calling {@link Message#getFormattedMessage()} first.<a name="line.27"></a> |
| <span class="sourceLineNo">028</span> * <p><a name="line.28"></a> |
| <span class="sourceLineNo">029</span> * Generally, logging mutable objects asynchronously always has the risk that the object is modified between the time<a name="line.29"></a> |
| <span class="sourceLineNo">030</span> * the logger is called and the time the log message is formatted and written to disk. Strictly speaking it is the<a name="line.30"></a> |
| <span class="sourceLineNo">031</span> * responsibility of the application to ensure that mutable objects are not modified after they have been logged,<a name="line.31"></a> |
| <span class="sourceLineNo">032</span> * but this is not always possible.<a name="line.32"></a> |
| <span class="sourceLineNo">033</span> * </p><p><a name="line.33"></a> |
| <span class="sourceLineNo">034</span> * Log4j prevents the above race condition as follows:<a name="line.34"></a> |
| <span class="sourceLineNo">035</span> * </p><ol><a name="line.35"></a> |
| <span class="sourceLineNo">036</span> * <li>If the Message implements {@link ReusableMessage}, asynchronous logging components in the Log4j implementation<a name="line.36"></a> |
| <span class="sourceLineNo">037</span> * will copy the message content (formatted message, parameters) onto the queue rather than passing the<a name="line.37"></a> |
| <span class="sourceLineNo">038</span> * {@code Message} instance itself. This ensures that the formatted message will not change<a name="line.38"></a> |
| <span class="sourceLineNo">039</span> * when the mutable object is modified.<a name="line.39"></a> |
| <span class="sourceLineNo">040</span> * </li><a name="line.40"></a> |
| <span class="sourceLineNo">041</span> * <li>If the Message is annotated with {@link AsynchronouslyFormattable}, it can be passed to another thread as is.</li><a name="line.41"></a> |
| <span class="sourceLineNo">042</span> * <li>Otherwise, asynchronous logging components in the Log4j implementation will call<a name="line.42"></a> |
| <span class="sourceLineNo">043</span> * {@link Message#getFormattedMessage()} before passing the Message object to another thread.<a name="line.43"></a> |
| <span class="sourceLineNo">044</span> * This gives the Message implementation class a chance to create a formatted message String with the current value<a name="line.44"></a> |
| <span class="sourceLineNo">045</span> * of the mutable object. The intention is that the Message implementation caches this formatted message and returns<a name="line.45"></a> |
| <span class="sourceLineNo">046</span> * it on subsequent calls.<a name="line.46"></a> |
| <span class="sourceLineNo">047</span> * (See <a href="https://issues.apache.org/jira/browse/LOG4J2-763">LOG4J2-763</a>.)<a name="line.47"></a> |
| <span class="sourceLineNo">048</span> * </li><a name="line.48"></a> |
| <span class="sourceLineNo">049</span> * </ol><a name="line.49"></a> |
| <span class="sourceLineNo">050</span> *<a name="line.50"></a> |
| <span class="sourceLineNo">051</span> * @see Message<a name="line.51"></a> |
| <span class="sourceLineNo">052</span> * @see ReusableMessage<a name="line.52"></a> |
| <span class="sourceLineNo">053</span> * @see <a href="https://issues.apache.org/jira/browse/LOG4J2-763">LOG4J2-763</a><a name="line.53"></a> |
| <span class="sourceLineNo">054</span> * @since 2.8<a name="line.54"></a> |
| <span class="sourceLineNo">055</span> */<a name="line.55"></a> |
| <span class="sourceLineNo">056</span>@Documented // This annotation is part of the public API of annotated elements.<a name="line.56"></a> |
| <span class="sourceLineNo">057</span>@Target(ElementType.TYPE) // Only applies to types.<a name="line.57"></a> |
| <span class="sourceLineNo">058</span>@Retention(RetentionPolicy.RUNTIME) //Needs to be reflectively discoverable runtime.<a name="line.58"></a> |
| <span class="sourceLineNo">059</span>public @interface AsynchronouslyFormattable {<a name="line.59"></a> |
| <span class="sourceLineNo">060</span>}<a name="line.60"></a> |
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