io.netty.util.DefaultAttributeMap Maven / Gradle / Ivy
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This artifact provides a single jar that contains all classes required to use remote EJB and JMS, including
all dependencies. It is intended for use by those not using maven, maven users should just import the EJB and
JMS 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).
/*
* 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;
import io.netty.util.internal.PlatformDependent;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.atomic.AtomicReferenceArray;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
/**
* Default {@link AttributeMap} implementation which use simple synchronization per bucket to keep the memory overhead
* as low as possible.
*/
public class DefaultAttributeMap implements AttributeMap {
@SuppressWarnings("rawtypes")
private static final AtomicReferenceFieldUpdater updater;
static {
@SuppressWarnings("rawtypes")
AtomicReferenceFieldUpdater referenceFieldUpdater =
PlatformDependent.newAtomicReferenceFieldUpdater(DefaultAttributeMap.class, "attributes");
if (referenceFieldUpdater == null) {
referenceFieldUpdater = AtomicReferenceFieldUpdater
.newUpdater(DefaultAttributeMap.class, AtomicReferenceArray.class, "attributes");
}
updater = referenceFieldUpdater;
}
private static final int BUCKET_SIZE = 4;
private static final int MASK = BUCKET_SIZE - 1;
// Initialize lazily to reduce memory consumption; updated by AtomicReferenceFieldUpdater above.
@SuppressWarnings("UnusedDeclaration")
private volatile AtomicReferenceArray> attributes;
@SuppressWarnings("unchecked")
@Override
public Attribute attr(AttributeKey key) {
if (key == null) {
throw new NullPointerException("key");
}
AtomicReferenceArray> attributes = this.attributes;
if (attributes == null) {
// Not using ConcurrentHashMap due to high memory consumption.
attributes = new AtomicReferenceArray>(BUCKET_SIZE);
if (!updater.compareAndSet(this, null, attributes)) {
attributes = this.attributes;
}
}
int i = index(key);
DefaultAttribute head = attributes.get(i);
if (head == null) {
// No head exists yet which means we may be able to add the attribute without synchronization and just
// use compare and set. At worst we need to fallback to synchronization
head = new DefaultAttribute(key);
if (attributes.compareAndSet(i, null, head)) {
// we were able to add it so return the head right away
return (Attribute) head;
} else {
head = attributes.get(i);
}
}
synchronized (head) {
DefaultAttribute curr = head;
for (;;) {
if (!curr.removed && curr.key == key) {
return (Attribute) curr;
}
DefaultAttribute next = curr.next;
if (next == null) {
DefaultAttribute attr = new DefaultAttribute(head, key);
curr.next = attr;
attr.prev = curr;
return attr;
} else {
curr = next;
}
}
}
}
private static int index(AttributeKey key) {
return key.id() & MASK;
}
@SuppressWarnings("serial")
private static final class DefaultAttribute extends AtomicReference implements Attribute {
private static final long serialVersionUID = -2661411462200283011L;
// The head of the linked-list this attribute belongs to, which may be itself
private final DefaultAttribute head;
private final AttributeKey key;
// Double-linked list to prev and next node to allow fast removal
private DefaultAttribute prev;
private DefaultAttribute next;
// Will be set to true one the attribute is removed via getAndRemove() or remove()
private volatile boolean removed;
DefaultAttribute(DefaultAttribute head, AttributeKey key) {
this.head = head;
this.key = key;
}
DefaultAttribute(AttributeKey key) {
head = this;
this.key = key;
}
@Override
public AttributeKey key() {
return key;
}
@Override
public T setIfAbsent(T value) {
while (!compareAndSet(null, value)) {
T old = get();
if (old != null) {
return old;
}
}
return null;
}
@Override
public T getAndRemove() {
removed = true;
T oldValue = getAndSet(null);
remove0();
return oldValue;
}
@Override
public void remove() {
removed = true;
set(null);
remove0();
}
private void remove0() {
synchronized (head) {
// We only update the linked-list structure if prev != null because if it is null this
// DefaultAttribute acts also as head. The head must never be removed completely and just be
// marked as removed as all synchronization is done on the head itself for each bucket.
// The head itself will be GC'ed once the DefaultAttributeMap is GC'ed. So at most 5 heads will
// be removed lazy as the array size is 5.
if (prev != null) {
prev.next = next;
if (next != null) {
next.prev = prev;
}
}
}
}
}
}