DefaultHandle Class — netty Architecture

Source Code

common/src/main/java/io/netty/util/Recycler.java lines 377–437

    private static final class DefaultHandle<T> extends EnhancedHandle<T> {
        private static final int STATE_CLAIMED = 0;
        private static final int STATE_AVAILABLE = 1;
        private static final AtomicIntegerFieldUpdater<DefaultHandle<?>> STATE_UPDATER;
        static {
            AtomicIntegerFieldUpdater<?> updater = AtomicIntegerFieldUpdater.newUpdater(DefaultHandle.class, "state");
            //noinspection unchecked
            STATE_UPDATER = (AtomicIntegerFieldUpdater<DefaultHandle<?>>) updater;
        }

        private volatile int state; // State is initialised to STATE_CLAIMED (aka. 0) so they can be released.
        private final GuardedLocalPool<T> localPool;
        private T value;

        DefaultHandle(GuardedLocalPool<T> localPool) {
            this.localPool = localPool;
        }

        @Override
        public void recycle(Object object) {
            if (object != value) {
                throw new IllegalArgumentException("object does not belong to handle");
            }
            toAvailable();
            localPool.release(this);
        }

        @Override
        public void unguardedRecycle(Object object) {
            if (object != value) {
                throw new IllegalArgumentException("object does not belong to handle");
            }
            unguardedToAvailable();
            localPool.release(this);
        }

        T claim() {
            assert state == STATE_AVAILABLE;
            STATE_UPDATER.lazySet(this, STATE_CLAIMED);
            return value;
        }

        void set(T value) {
            this.value = value;
        }

        private void toAvailable() {
            int prev = STATE_UPDATER.getAndSet(this, STATE_AVAILABLE);
            if (prev == STATE_AVAILABLE) {
                throw new IllegalStateException("Object has been recycled already.");
            }
        }

        private void unguardedToAvailable() {
            int prev = state;
            if (prev == STATE_AVAILABLE) {
                throw new IllegalStateException("Object has been recycled already.");
            }
            STATE_UPDATER.lazySet(this, STATE_AVAILABLE);
        }
    }