AddressResolverGroup Class — netty Architecture

Source Code

resolver/src/main/java/io/netty/resolver/AddressResolverGroup.java lines 36–128

public abstract class AddressResolverGroup<T extends SocketAddress> implements Closeable {

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(AddressResolverGroup.class);

    /**
     * Note that we do not use a {@link ConcurrentMap} here because it is usually expensive to instantiate a resolver.
     */
    private final Map<EventExecutor, AddressResolver<T>> resolvers =
            new IdentityHashMap<EventExecutor, AddressResolver<T>>();

    private final Map<EventExecutor, GenericFutureListener<Future<Object>>> executorTerminationListeners =
            new IdentityHashMap<EventExecutor, GenericFutureListener<Future<Object>>>();

    protected AddressResolverGroup() { }

    /**
     * Returns the {@link AddressResolver} associated with the specified {@link EventExecutor}. If there's no associated
     * resolver found, this method creates and returns a new resolver instance created by
     * {@link #newResolver(EventExecutor)} so that the new resolver is reused on another
     * {@code #getResolver(EventExecutor)} call with the same {@link EventExecutor}.
     */
    public AddressResolver<T> getResolver(final EventExecutor executor) {
        ObjectUtil.checkNotNull(executor, "executor");

        if (executor.isShuttingDown()) {
            throw new IllegalStateException("executor not accepting a task");
        }

        AddressResolver<T> r;
        synchronized (resolvers) {
            r = resolvers.get(executor);
            if (r == null) {
                final AddressResolver<T> newResolver;
                try {
                    newResolver = newResolver(executor);
                } catch (Exception e) {
                    throw new IllegalStateException("failed to create a new resolver", e);
                }

                resolvers.put(executor, newResolver);

                final FutureListener<Object> terminationListener = future -> {
                    synchronized (resolvers) {
                        resolvers.remove(executor);
                        executorTerminationListeners.remove(executor);
                    }
                    newResolver.close();
                };

                executorTerminationListeners.put(executor, terminationListener);
                executor.terminationFuture().addListener(terminationListener);

                r = newResolver;
            }
        }

        return r;
    }

    /**
     * Invoked by {@link #getResolver(EventExecutor)} to create a new {@link AddressResolver}.
     */
    protected abstract AddressResolver<T> newResolver(EventExecutor executor) throws Exception;

    /**
     * Closes all {@link NameResolver}s created by this group.
     */
    @Override
    @SuppressWarnings({ "unchecked", "SuspiciousToArrayCall" })
    public void close() {
        final AddressResolver<T>[] rArray;
        final Map.Entry<EventExecutor, GenericFutureListener<Future<Object>>>[] listeners;

        synchronized (resolvers) {
            rArray = (AddressResolver<T>[]) resolvers.values().toArray(new AddressResolver[0]);
            resolvers.clear();
            listeners = executorTerminationListeners.entrySet().toArray(new Map.Entry[0]);
            executorTerminationListeners.clear();
        }

        for (final Map.Entry<EventExecutor, GenericFutureListener<Future<Object>>> entry : listeners) {