HashedWheelTimeout Class — netty Architecture

Source Code

common/src/main/java/io/netty/util/HashedWheelTimer.java lines 612–753

    private static final class HashedWheelTimeout implements Timeout, Runnable {

        private static final int ST_INIT = 0;
        private static final int ST_CANCELLED = 1;
        private static final int ST_EXPIRED = 2;
        private static final AtomicIntegerFieldUpdater<HashedWheelTimeout> STATE_UPDATER =
                AtomicIntegerFieldUpdater.newUpdater(HashedWheelTimeout.class, "state");

        private final HashedWheelTimer timer;
        private final TimerTask task;
        private final long deadline;

        @SuppressWarnings({"unused", "FieldMayBeFinal", "RedundantFieldInitialization" })
        private volatile int state = ST_INIT;

        // remainingRounds will be calculated and set by Worker.transferTimeoutsToBuckets() before the
        // HashedWheelTimeout will be added to the correct HashedWheelBucket.
        long remainingRounds;

        // This will be used to chain timeouts in HashedWheelTimerBucket via a double-linked-list.
        // As only the workerThread will act on it there is no need for synchronization / volatile.
        HashedWheelTimeout next;
        HashedWheelTimeout prev;

        // The bucket to which the timeout was added
        HashedWheelBucket bucket;

        HashedWheelTimeout(HashedWheelTimer timer, TimerTask task, long deadline) {
            this.timer = timer;
            this.task = task;
            this.deadline = deadline;
        }

        @Override
        public Timer timer() {
            return timer;
        }

        @Override
        public TimerTask task() {
            return task;
        }

        @Override
        public boolean cancel() {
            // only update the state it will be removed from HashedWheelBucket on next tick.
            if (!compareAndSetState(ST_INIT, ST_CANCELLED)) {
                return false;
            }
            // If a task should be canceled we put this to another queue which will be processed on each tick.
            // So this means that we will have a GC latency of max. 1 tick duration which is good enough. This way
            // we can make again use of our MpscLinkedQueue and so minimize the locking / overhead as much as possible.
            timer.cancelledTimeouts.add(this);
            return true;
        }

        private void remove() {
            HashedWheelBucket bucket = this.bucket;
            if (bucket != null) {
                bucket.remove(this);
            }
            timer.pendingTimeouts.decrementAndGet();
        }
        void removeAfterCancellation() {
            remove();
            task.cancelled(this);
        }

        public boolean compareAndSetState(int expected, int state) {
            return STATE_UPDATER.compareAndSet(this, expected, state);
        }

        public int state() {
            return state;
        }

        @Override
        public boolean isCancelled() {
            return state() == ST_CANCELLED;
        }