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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache license, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the license for the specific language governing permissions and
 * limitations under the license.
 */
package org.apache.logging.log4j.message;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Annotation that signals to asynchronous logging components that messages of this type can safely be passed to
 * a background thread without calling {@link Message#getFormattedMessage()} first.
 * 

* Generally, logging mutable objects asynchronously always has the risk that the object is modified between the time * the logger is called and the time the log message is formatted and written to disk. Strictly speaking it is the * responsibility of the application to ensure that mutable objects are not modified after they have been logged, * but this is not always possible. *

* Log4j prevents the above race condition as follows: *

    *
  1. If the Message implements {@link ReusableMessage}, asynchronous logging components in the Log4j implementation * will copy the message content (formatted message, parameters) onto the queue rather than passing the * {@code Message} instance itself. This ensures that the formatted message will not change * when the mutable object is modified. *
  2. *
  3. If the Message is annotated with {@link AsynchronouslyFormattable}, it can be passed to another thread as is.
  4. *
  5. Otherwise, asynchronous logging components in the Log4j implementation will call * {@link Message#getFormattedMessage()} before passing the Message object to another thread. * This gives the Message implementation class a chance to create a formatted message String with the current value * of the mutable object. The intention is that the Message implementation caches this formatted message and returns * it on subsequent calls. * (See LOG4J2-763.) *
  6. *
* * @see Message * @see ReusableMessage * @see LOG4J2-763 * @since 2.8 */ @Documented // This annotation is part of the public API of annotated elements. @Target(ElementType.TYPE) // Only applies to types. @Retention(RetentionPolicy.RUNTIME) //Needs to be reflectively discoverable runtime. public @interface AsynchronouslyFormattable { }




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