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This artifact provides a single jar that contains all classes required to use remote Jakarta Enterprise Beans and Jakarta Messaging, including all dependencies. It is intended for use by those not using maven, maven users should just import the Jakarta Enterprise Beans and Jakarta Messaging BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up with different versions on classes on the class path).

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/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project 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 io.netty.util;

/**
 * An attribute which allows to store a value reference. It may be updated atomically and so is thread-safe.
 *
 * @param    the type of the value it holds.
 */
public interface Attribute {

    /**
     * Returns the key of this attribute.
     */
    AttributeKey key();

    /**
     * Returns the current value, which may be {@code null}
     */
    T get();

    /**
     * Sets the value
     */
    void set(T value);

    /**
     *  Atomically sets to the given value and returns the old value which may be {@code null} if non was set before.
     */
    T getAndSet(T value);

    /**
     *  Atomically sets to the given value if this {@link Attribute} does not contain a value at the moment.
     *  If it was not possible to set the value as it contains a value it will just return the current value.
     */
    T setIfAbsent(T value);

    /**
     * Removes this attribute from the {@link AttributeMap} and returns the old value..  Subsequent {@link #get()}
     * calls will return @{code null}.
     */
    T getAndRemove();

    /**
     * Atomically sets the value to the given updated value if the current value == the expected value.
     * If it the set was successful it returns {@code true} otherwise {@code false}.
     */
    boolean compareAndSet(T oldValue, T newValue);

    /**
     * Removes this attribute from the {@link AttributeMap}.  Subsequent {@link #get()} calls will return @{code null}.
     */
    void remove();
}