7f8b5f8efd
Motivation: Using Attribute.remove() and Attribute.getAndRemove() in a multi-threaded enviroment has its drawbacks. Make sure we document these. Modifications: Add javadocs and mark Attribute.remove() and Attribute.getAndRemove() as @Deprecated. Result: Hopefully less suprising behaviour.
94 lines
3.8 KiB
Java
94 lines
3.8 KiB
Java
/*
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* Copyright 2012 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License,
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* version 2.0 (the "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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package io.netty.util;
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/**
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* An attribute which allows to store a value reference. It may be updated atomically and so is thread-safe.
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*
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* @param <T> the type of the value it holds.
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*/
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public interface Attribute<T> {
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/**
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* Returns the key of this attribute.
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*/
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AttributeKey<T> key();
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/**
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* Returns the current value, which may be {@code null}
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*/
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T get();
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/**
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* Sets the value
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*/
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void set(T value);
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/**
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* Atomically sets to the given value and returns the old value which may be {@code null} if non was set before.
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*/
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T getAndSet(T value);
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/**
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* Atomically sets to the given value if this {@link Attribute}'s value is {@code null}.
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* If it was not possible to set the value as it contains a value it will just return the current value.
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*/
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T setIfAbsent(T value);
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/**
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* Removes this attribute from the {@link AttributeMap} and returns the old value. Subsequent {@link #get()}
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* calls will return {@code null}.
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*
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* If you only want to return the old value and clear the {@link Attribute} while still keep it in the
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* {@link AttributeMap} use {@link #getAndSet(Object)} with a value of {@code null}.
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*
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* <p>
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* Be aware that even if you call this method another thread that has obtained a reference to this {@link Attribute}
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* via {@link AttributeMap#attr(AttributeKey)} will still operate on the same instance. That said if now another
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* thread or even the same thread later will call {@link AttributeMap#attr(AttributeKey)} again, a new
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* {@link Attribute} instance is created and so is not the same as the previous one that was removed. Because of
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* this special caution should be taken when you call {@link #remove()} or {@link #getAndRemove()}.
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*
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* @deprecated please consider using {@link #getAndSet(Object)} (with value of {@code null}).
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*/
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@Deprecated
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T getAndRemove();
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/**
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* Atomically sets the value to the given updated value if the current value == the expected value.
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* If it the set was successful it returns {@code true} otherwise {@code false}.
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*/
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boolean compareAndSet(T oldValue, T newValue);
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/**
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* Removes this attribute from the {@link AttributeMap}. Subsequent {@link #get()} calls will return @{code null}.
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*
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* If you only want to remove the value and clear the {@link Attribute} while still keep it in
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* {@link AttributeMap} use {@link #set(Object)} with a value of {@code null}.
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*
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* <p>
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* Be aware that even if you call this method another thread that has obtained a reference to this {@link Attribute}
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* via {@link AttributeMap#attr(AttributeKey)} will still operate on the same instance. That said if now another
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* thread or even the same thread later will call {@link AttributeMap#attr(AttributeKey)} again, a new
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* {@link Attribute} instance is created and so is not the same as the previous one that was removed. Because of
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* this special caution should be taken when you call {@link #remove()} or {@link #getAndRemove()}.
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*
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* @deprecated please consider using {@link #set(Object)} (with value of {@code null}).
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*/
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@Deprecated
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void remove();
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}
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