DefaultAttribute Class — netty Architecture

Source Code

common/src/main/java/io/netty/util/DefaultAttributeMap.java lines 156–212

    @SuppressWarnings("serial")
    private static final class DefaultAttribute<T> extends AtomicReference<T> implements Attribute<T> {

        private static final AtomicReferenceFieldUpdater<DefaultAttribute, DefaultAttributeMap> MAP_UPDATER =
                AtomicReferenceFieldUpdater.newUpdater(DefaultAttribute.class,
                                                       DefaultAttributeMap.class, "attributeMap");
        private static final long serialVersionUID = -2661411462200283011L;

        private volatile DefaultAttributeMap attributeMap;
        private final AttributeKey<T> key;

        DefaultAttribute(DefaultAttributeMap attributeMap, AttributeKey<T> key) {
            this.attributeMap = attributeMap;
            this.key = key;
        }

        @Override
        public AttributeKey<T> 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);
            }
        }
    }