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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).
/*
* 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 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 =
AtomicReferenceFieldUpdater.newUpdater(DefaultAttributeMap.class, AtomicReferenceArray.class, "attributes");
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 and waste two allocations.
head = new DefaultAttribute();
DefaultAttribute attr = new DefaultAttribute(head, key);
head.next = attr;
attr.prev = head;
if (attributes.compareAndSet(i, null, head)) {
// we were able to add it so return the attr right away
return attr;
} else {
head = attributes.get(i);
}
}
synchronized (head) {
DefaultAttribute curr = head;
for (;;) {
DefaultAttribute next = curr.next;
if (next == null) {
DefaultAttribute attr = new DefaultAttribute(head, key);
curr.next = attr;
attr.prev = curr;
return attr;
}
if (next.key == key && !next.removed) {
return (Attribute) next;
}
curr = next;
}
}
}
@Override
public boolean hasAttr(AttributeKey key) {
if (key == null) {
throw new NullPointerException("key");
}
AtomicReferenceArray> attributes = this.attributes;
if (attributes == null) {
// no attribute exists
return false;
}
int i = index(key);
DefaultAttribute head = attributes.get(i);
if (head == null) {
// No attribute exists which point to the bucket in which the head should be located
return false;
}
// We need to synchronize on the head.
synchronized (head) {
// Start with head.next as the head itself does not store an attribute.
DefaultAttribute curr = head.next;
while (curr != null) {
if (curr.key == key && !curr.removed) {
return true;
}
curr = curr.next;
}
return false;
}
}
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
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;
}
// Special constructor for the head of the linked-list.
DefaultAttribute() {
head = this;
key = null;
}
@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) {
if (prev == null) {
// Removed before.
return;
}
prev.next = next;
if (next != null) {
next.prev = prev;
}
// Null out prev and next - this will guard against multiple remove0() calls which may corrupt
// the linked list for the bucket.
prev = null;
next = null;
}
}
}
}
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