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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 ch.cern.hbase.thirdparty.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}'s value is {@code null}.
* 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}.
*
* If you only want to return the old value and clear the {@link Attribute} while still keep it in the
* {@link AttributeMap} use {@link #getAndSet(Object)} with a value of {@code null}.
*
*
* Be aware that even if you call this method another thread that has obtained a reference to this {@link Attribute}
* via {@link AttributeMap#attr(AttributeKey)} will still operate on the same instance. That said if now another
* thread or even the same thread later will call {@link AttributeMap#attr(AttributeKey)} again, a new
* {@link Attribute} instance is created and so is not the same as the previous one that was removed. Because of
* this special caution should be taken when you call {@link #remove()} or {@link #getAndRemove()}.
*
* @deprecated please consider using {@link #getAndSet(Object)} (with value of {@code null}).
*/
@Deprecated
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}.
*
* If you only want to remove the value and clear the {@link Attribute} while still keep it in
* {@link AttributeMap} use {@link #set(Object)} with a value of {@code null}.
*
*
* Be aware that even if you call this method another thread that has obtained a reference to this {@link Attribute}
* via {@link AttributeMap#attr(AttributeKey)} will still operate on the same instance. That said if now another
* thread or even the same thread later will call {@link AttributeMap#attr(AttributeKey)} again, a new
* {@link Attribute} instance is created and so is not the same as the previous one that was removed. Because of
* this special caution should be taken when you call {@link #remove()} or {@link #getAndRemove()}.
*
* @deprecated please consider using {@link #set(Object)} (with value of {@code null}).
*/
@Deprecated
void remove();
}