org.xbib.helianthus.internal.DefaultAttributeMap Maven / Gradle / Ivy
package org.xbib.helianthus.internal;
import io.netty.util.Attribute;
import io.netty.util.AttributeKey;
import io.netty.util.AttributeMap;
import java.util.Collections;
import java.util.Iterator;
import java.util.NoSuchElementException;
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.
* Note: This class has been forked from {@link io.netty.util.DefaultAttributeMap}.
*/
public class DefaultAttributeMap implements AttributeMap {
@SuppressWarnings({"rawtypes", "AtomicFieldUpdaterIssues"})
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")
volatile AtomicReferenceArray> attributes;
private static int index(AttributeKey key) {
return key.id() & MASK;
}
@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;
}
}
}
}
@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;
}
// check on the head can be done without synchronization
if (head.key == key && !head.removed) {
return true;
}
synchronized (head) {
// we need to synchronize on the head
DefaultAttribute curr = head.next;
while (curr != null) {
if (!curr.removed && curr.key == key) {
return true;
}
curr = curr.next;
}
return false;
}
}
public Iterator> attrs() {
final AtomicReferenceArray> attributes = this.attributes;
if (attributes == null) {
return Collections.emptyIterator();
}
return new IteratorImpl(attributes);
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
for (Iterator> i = attrs(); i.hasNext(); ) {
final Attribute a = i.next();
if (sb.length() > 0) {
sb.append(',');
}
sb.append(a.key().name()).append('=').append(a.get());
}
return sb.toString();
}
@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;
}
@SuppressWarnings("deprecation")
@Override
public T getAndRemove() {
removed = true;
T oldValue = getAndSet(null);
remove0();
return oldValue;
}
@SuppressWarnings("deprecation")
@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;
}
// 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;
}
}
}
}
private static final class IteratorImpl implements Iterator> {
private final AtomicReferenceArray> attributes;
private int i = -1;
private DefaultAttribute next;
IteratorImpl(AtomicReferenceArray> attributes) {
this.attributes = attributes;
next = findNext(null);
}
@Override
public boolean hasNext() {
return next != null;
}
@Override
public Attribute next() {
if (next == null) {
throw new NoSuchElementException();
}
final DefaultAttribute next = this.next;
this.next = findNext(next.next);
return next;
}
private DefaultAttribute findNext(DefaultAttribute next) {
while (true) {
if (next == null) {
for (i++; i < attributes.length(); i++) {
final DefaultAttribute attr = attributes.get(i);
if (attr != null) {
next = attr;
break;
}
}
if (i == attributes.length()) {
return null;
}
}
boolean found = false;
while (next != null && next.removed) {
if ((next = next.next) == null) {
found = true;
break;
}
}
if (!found) {
return next;
}
}
}
}
}
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