107 lines
3.3 KiB
Java
107 lines
3.3 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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import java.util.IdentityHashMap;
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import java.util.Map;
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import java.util.concurrent.atomic.AtomicReference;
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import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
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/**
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* Default {@link AttributeMap} implementation which use simple synchronization to keep the memory overhead
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* as low as possible.
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*/
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public class DefaultAttributeMap implements AttributeMap {
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@SuppressWarnings("rawtypes")
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private static final AtomicReferenceFieldUpdater<DefaultAttributeMap, Map> updater =
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AtomicReferenceFieldUpdater.newUpdater(DefaultAttributeMap.class, Map.class, "map");
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// Initialize lazily to reduce memory consumption; updated by AtomicReferenceFieldUpdater above.
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@SuppressWarnings("UnusedDeclaration")
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private volatile Map<AttributeKey<?>, Attribute<?>> map;
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@Override
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public <T> Attribute<T> attr(AttributeKey<T> key) {
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Map<AttributeKey<?>, Attribute<?>> map = this.map;
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if (map == null) {
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// Not using ConcurrentHashMap due to high memory consumption.
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map = new IdentityHashMap<AttributeKey<?>, Attribute<?>>(2);
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if (!updater.compareAndSet(this, null, map)) {
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map = this.map;
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}
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}
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synchronized (map) {
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@SuppressWarnings("unchecked")
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Attribute<T> attr = (Attribute<T>) map.get(key);
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if (attr == null) {
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attr = new DefaultAttribute<T>(map, key);
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map.put(key, attr);
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}
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return attr;
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}
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}
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private static final class DefaultAttribute<T> extends AtomicReference<T> implements Attribute<T> {
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private static final long serialVersionUID = -2661411462200283011L;
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private final Map<AttributeKey<?>, Attribute<?>> map;
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private final AttributeKey<T> key;
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DefaultAttribute(Map<AttributeKey<?>, Attribute<?>> map, AttributeKey<T> key) {
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this.map = map;
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this.key = key;
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}
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@Override
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public AttributeKey<T> key() {
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return key;
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}
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@Override
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public T setIfAbsent(T value) {
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while (!compareAndSet(null, value)) {
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T old = get();
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if (old != null) {
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return old;
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}
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}
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return null;
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}
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@Override
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public T getAndRemove() {
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T oldValue = getAndSet(null);
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remove0();
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return oldValue;
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}
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@Override
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public void remove() {
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set(null);
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remove0();
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}
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private void remove0() {
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synchronized (map) {
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map.remove(key);
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}
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}
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}
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}
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