io.netty.util.DefaultAttributeMap Maven / Gradle / Ivy
/*
* 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:
*
* https://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.ObjectUtil;
import java.util.Arrays;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
/**
* Default {@link AttributeMap} implementation which not exibit any blocking behaviour on attribute lookup while using a
* copy-on-write approach on the modify path.
Attributes lookup and remove exibit {@code O(logn)} time worst-case
* complexity, hence {@code attribute::set(null)} is to be preferred to {@code remove}.
*/
public class DefaultAttributeMap implements AttributeMap {
private static final AtomicReferenceFieldUpdater ATTRIBUTES_UPDATER =
AtomicReferenceFieldUpdater.newUpdater(DefaultAttributeMap.class, DefaultAttribute[].class, "attributes");
private static final DefaultAttribute[] EMPTY_ATTRIBUTES = new DefaultAttribute[0];
/**
* Similarly to {@code Arrays::binarySearch} it perform a binary search optimized for this use case, in order to
* save polymorphic calls (on comparator side) and unnecessary class checks.
*/
private static int searchAttributeByKey(DefaultAttribute[] sortedAttributes, AttributeKey key) {
int low = 0;
int high = sortedAttributes.length - 1;
while (low <= high) {
int mid = low + high >>> 1;
DefaultAttribute midVal = sortedAttributes[mid];
AttributeKey midValKey = midVal.key;
if (midValKey == key) {
return mid;
}
int midValKeyId = midValKey.id();
int keyId = key.id();
assert midValKeyId != keyId;
boolean searchRight = midValKeyId < keyId;
if (searchRight) {
low = mid + 1;
} else {
high = mid - 1;
}
}
return -(low + 1);
}
private static void orderedCopyOnInsert(DefaultAttribute[] sortedSrc, int srcLength, DefaultAttribute[] copy,
DefaultAttribute toInsert) {
// let's walk backward, because as a rule of thumb, toInsert.key.id() tends to be higher for new keys
final int id = toInsert.key.id();
int i;
for (i = srcLength - 1; i >= 0; i--) {
DefaultAttribute attribute = sortedSrc[i];
assert attribute.key.id() != id;
if (attribute.key.id() < id) {
break;
}
copy[i + 1] = sortedSrc[i];
}
copy[i + 1] = toInsert;
final int toCopy = i + 1;
if (toCopy > 0) {
System.arraycopy(sortedSrc, 0, copy, 0, toCopy);
}
}
private volatile DefaultAttribute[] attributes = EMPTY_ATTRIBUTES;
@SuppressWarnings("unchecked")
@Override
public Attribute attr(AttributeKey key) {
ObjectUtil.checkNotNull(key, "key");
DefaultAttribute newAttribute = null;
for (;;) {
final DefaultAttribute[] attributes = this.attributes;
final int index = searchAttributeByKey(attributes, key);
final DefaultAttribute[] newAttributes;
if (index >= 0) {
final DefaultAttribute attribute = attributes[index];
assert attribute.key() == key;
if (!attribute.isRemoved()) {
return attribute;
}
// let's try replace the removed attribute with a new one
if (newAttribute == null) {
newAttribute = new DefaultAttribute(this, key);
}
final int count = attributes.length;
newAttributes = Arrays.copyOf(attributes, count);
newAttributes[index] = newAttribute;
} else {
if (newAttribute == null) {
newAttribute = new DefaultAttribute(this, key);
}
final int count = attributes.length;
newAttributes = new DefaultAttribute[count + 1];
orderedCopyOnInsert(attributes, count, newAttributes, newAttribute);
}
if (ATTRIBUTES_UPDATER.compareAndSet(this, attributes, newAttributes)) {
return newAttribute;
}
}
}
@Override
public boolean hasAttr(AttributeKey key) {
ObjectUtil.checkNotNull(key, "key");
return searchAttributeByKey(attributes, key) >= 0;
}
private void removeAttributeIfMatch(AttributeKey key, DefaultAttribute value) {
for (;;) {
final DefaultAttribute[] attributes = this.attributes;
final int index = searchAttributeByKey(attributes, key);
if (index < 0) {
return;
}
final DefaultAttribute attribute = attributes[index];
assert attribute.key() == key;
if (attribute != value) {
return;
}
final int count = attributes.length;
final int newCount = count - 1;
final DefaultAttribute[] newAttributes =
newCount == 0? EMPTY_ATTRIBUTES : new DefaultAttribute[newCount];
// perform 2 bulk copies
System.arraycopy(attributes, 0, newAttributes, 0, index);
final int remaining = count - index - 1;
if (remaining > 0) {
System.arraycopy(attributes, index + 1, newAttributes, index, remaining);
}
if (ATTRIBUTES_UPDATER.compareAndSet(this, attributes, newAttributes)) {
return;
}
}
}
@SuppressWarnings("serial")
private static final class DefaultAttribute extends AtomicReference implements Attribute {
private static final AtomicReferenceFieldUpdater MAP_UPDATER =
AtomicReferenceFieldUpdater.newUpdater(DefaultAttribute.class,
DefaultAttributeMap.class, "attributeMap");
private static final long serialVersionUID = -2661411462200283011L;
private volatile DefaultAttributeMap attributeMap;
private final AttributeKey key;
DefaultAttribute(DefaultAttributeMap attributeMap, AttributeKey key) {
this.attributeMap = attributeMap;
this.key = key;
}
@Override
public AttributeKey key() {
return key;
}
private boolean isRemoved() {
return attributeMap == null;
}
@Override
public T setIfAbsent(T value) {
while (!compareAndSet(null, value)) {
T old = get();
if (old != null) {
return old;
}
}
return null;
}
@Override
public T getAndRemove() {
final DefaultAttributeMap attributeMap = this.attributeMap;
final boolean removed = attributeMap != null && MAP_UPDATER.compareAndSet(this, attributeMap, null);
T oldValue = getAndSet(null);
if (removed) {
attributeMap.removeAttributeIfMatch(key, this);
}
return oldValue;
}
@Override
public void remove() {
final DefaultAttributeMap attributeMap = this.attributeMap;
final boolean removed = attributeMap != null && MAP_UPDATER.compareAndSet(this, attributeMap, null);
set(null);
if (removed) {
attributeMap.removeAttributeIfMatch(key, this);
}
}
}
}
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