BlockingMessageQueue Class — netty Architecture

Source Code

common/src/main/java/io/netty/util/Recycler.java lines 623–728

    private static final class BlockingMessageQueue<T> implements MessagePassingQueue<T> {
        private final Queue<T> deque;
        private final int maxCapacity;

        BlockingMessageQueue(int maxCapacity) {
            this.maxCapacity = maxCapacity;
            // This message passing queue is backed by an ArrayDeque instance,
            // made thread-safe by synchronising on `this` BlockingMessageQueue instance.
            // Why ArrayDeque?
            // We use ArrayDeque instead of LinkedList or LinkedBlockingQueue because it's more space efficient.
            // We use ArrayDeque instead of ArrayList because we need the queue APIs.
            // We use ArrayDeque instead of ConcurrentLinkedQueue because CLQ is unbounded and has O(n) size().
            // We use ArrayDeque instead of ArrayBlockingQueue because ABQ allocates its max capacity up-front,
            // and these queues will usually have large capacities, in potentially great numbers (one per thread),
            // but often only have comparatively few items in them.
            deque = new ArrayDeque<T>();
        }

        @Override
        public synchronized boolean offer(T e) {
            if (deque.size() == maxCapacity) {
                return false;
            }
            return deque.offer(e);
        }

        @Override
        public synchronized T poll() {
            return deque.poll();
        }

        @Override
        public synchronized T peek() {
            return deque.peek();
        }

        @Override
        public synchronized int size() {
            return deque.size();
        }

        @Override
        public synchronized void clear() {
            deque.clear();
        }

        @Override
        public synchronized boolean isEmpty() {
            return deque.isEmpty();
        }

        @Override
        public int capacity() {
            return maxCapacity;
        }

        @Override
        public boolean relaxedOffer(T e) {
            return offer(e);
        }

        @Override
        public T relaxedPoll() {
            return poll();
        }

        @Override
        public T relaxedPeek() {
            return peek();
        }

        @Override
        public int drain(Consumer<T> c, int limit) {
            T obj;
            int i = 0;
            for (; i < limit && (obj = poll()) != null; i++) {
                c.accept(obj);
            }
            return i;
        }