聊聊elasticsearch的SeedHostsResolver

    public interface ConfiguredHostsResolver {
        /**
         * Attempt to resolve the configured unicast hosts list to a list of transport addresses.
         *
         * @param consumer Consumer for the resolved list. May not be called if an error occurs or if another resolution attempt is in
         *                 progress.
         */
        void resolveConfiguredHosts(Consumer<List<TransportAddress>> consumer);
    }

public class SeedHostsResolver extends AbstractLifecycleComponent implements ConfiguredHostsResolver {
    public static final Setting<Integer> LEGACY_DISCOVERY_ZEN_PING_UNICAST_CONCURRENT_CONNECTS_SETTING =
        Setting.intSetting("discovery.zen.ping.unicast.concurrent_connects", 10, 0, Setting.Property.NodeScope,
            Setting.Property.Deprecated);
    public static final Setting<TimeValue> LEGACY_DISCOVERY_ZEN_PING_UNICAST_HOSTS_RESOLVE_TIMEOUT =
        Setting.positiveTimeSetting("discovery.zen.ping.unicast.hosts.resolve_timeout", TimeValue.timeValueSeconds(5),
            Setting.Property.NodeScope, Setting.Property.Deprecated);
    public static final Setting<Integer> DISCOVERY_SEED_RESOLVER_MAX_CONCURRENT_RESOLVERS_SETTING =
        Setting.intSetting("discovery.seed_resolver.max_concurrent_resolvers", 10, 0, Setting.Property.NodeScope);
    public static final Setting<TimeValue> DISCOVERY_SEED_RESOLVER_TIMEOUT_SETTING =
        Setting.positiveTimeSetting("discovery.seed_resolver.timeout", TimeValue.timeValueSeconds(5), Setting.Property.NodeScope);
​
    private static final Logger logger = LogManager.getLogger(SeedHostsResolver.class);
​
    private final Settings settings;
    private final AtomicBoolean resolveInProgress = new AtomicBoolean();
    private final TransportService transportService;
    private final SeedHostsProvider hostsProvider;
    private final SetOnce<ExecutorService> executorService = new SetOnce<>();
    private final TimeValue resolveTimeout;
    private final String nodeName;
    private final int concurrentConnects;
​
    public SeedHostsResolver(String nodeName, Settings settings, TransportService transportService,
                             SeedHostsProvider seedProvider) {
        this.settings = settings;
        this.nodeName = nodeName;
        this.transportService = transportService;
        this.hostsProvider = seedProvider;
        resolveTimeout = getResolveTimeout(settings);
        concurrentConnects = getMaxConcurrentResolvers(settings);
    }
​
    public static int getMaxConcurrentResolvers(Settings settings) {
        if (LEGACY_DISCOVERY_ZEN_PING_UNICAST_CONCURRENT_CONNECTS_SETTING.exists(settings)) {
            if (DISCOVERY_SEED_RESOLVER_MAX_CONCURRENT_RESOLVERS_SETTING.exists(settings)) {
                throw new IllegalArgumentException("it is forbidden to set both ["
                    + DISCOVERY_SEED_RESOLVER_MAX_CONCURRENT_RESOLVERS_SETTING.getKey() + "] and ["
                    + LEGACY_DISCOVERY_ZEN_PING_UNICAST_CONCURRENT_CONNECTS_SETTING.getKey() + "]");
            }
            return LEGACY_DISCOVERY_ZEN_PING_UNICAST_CONCURRENT_CONNECTS_SETTING.get(settings);
        }
        return DISCOVERY_SEED_RESOLVER_MAX_CONCURRENT_RESOLVERS_SETTING.get(settings);
    }
​
    public static TimeValue getResolveTimeout(Settings settings) {
        if (LEGACY_DISCOVERY_ZEN_PING_UNICAST_HOSTS_RESOLVE_TIMEOUT.exists(settings)) {
            if (DISCOVERY_SEED_RESOLVER_TIMEOUT_SETTING.exists(settings)) {
                throw new IllegalArgumentException("it is forbidden to set both ["
                    + DISCOVERY_SEED_RESOLVER_TIMEOUT_SETTING.getKey() + "] and ["
                    + LEGACY_DISCOVERY_ZEN_PING_UNICAST_HOSTS_RESOLVE_TIMEOUT.getKey() + "]");
            }
            return LEGACY_DISCOVERY_ZEN_PING_UNICAST_HOSTS_RESOLVE_TIMEOUT.get(settings);
        }
        return DISCOVERY_SEED_RESOLVER_TIMEOUT_SETTING.get(settings);
    }
​
    /**
     * Resolves a list of hosts to a list of transport addresses. Each host is resolved into a transport address (or a collection of
     * addresses if the number of ports is greater than one). Host lookups are done in parallel using specified executor service up
     * to the specified resolve timeout.
     *
     * @param executorService  the executor service used to parallelize hostname lookups
     * @param logger           logger used for logging messages regarding hostname lookups
     * @param hosts            the hosts to resolve
     * @param limitPortCounts  the number of ports to resolve (should be 1 for non-local transport)
     * @param transportService the transport service
     * @param resolveTimeout   the timeout before returning from hostname lookups
     * @return a list of resolved transport addresses
     */
    public static List<TransportAddress> resolveHostsLists(
        final ExecutorService executorService,
        final Logger logger,
        final List<String> hosts,
        final int limitPortCounts,
        final TransportService transportService,
        final TimeValue resolveTimeout) {
        Objects.requireNonNull(executorService);
        Objects.requireNonNull(logger);
        Objects.requireNonNull(hosts);
        Objects.requireNonNull(transportService);
        Objects.requireNonNull(resolveTimeout);
        if (resolveTimeout.nanos() < 0) {
            throw new IllegalArgumentException("resolve timeout must be non-negative but was [" + resolveTimeout + "]");
        }
        // create tasks to submit to the executor service; we will wait up to resolveTimeout for these tasks to complete
        final List<Callable<TransportAddress[]>> callables =
            hosts
                .stream()
                .map(hn -> (Callable<TransportAddress[]>) () -> transportService.addressesFromString(hn, limitPortCounts))
                .collect(Collectors.toList());
        final List<Future<TransportAddress[]>> futures;
        try {
            futures = executorService.invokeAll(callables, resolveTimeout.nanos(), TimeUnit.NANOSECONDS);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            return Collections.emptyList();
        }
        final List<TransportAddress> transportAddresses = new ArrayList<>();
        final Set<TransportAddress> localAddresses = new HashSet<>();
        localAddresses.add(transportService.boundAddress().publishAddress());
        localAddresses.addAll(Arrays.asList(transportService.boundAddress().boundAddresses()));
        // ExecutorService#invokeAll guarantees that the futures are returned in the iteration order of the tasks so we can associate the
        // hostname with the corresponding task by iterating together
        final Iterator<String> it = hosts.iterator();
        for (final Future<TransportAddress[]> future : futures) {
            final String hostname = it.next();
            if (!future.isCancelled()) {
                assert future.isDone();
                try {
                    final TransportAddress[] addresses = future.get();
                    logger.trace("resolved host [{}] to {}", hostname, addresses);
                    for (int addressId = 0; addressId < addresses.length; addressId++) {
                        final TransportAddress address = addresses[addressId];
                        // no point in pinging ourselves
                        if (localAddresses.contains(address) == false) {
                            transportAddresses.add(address);
                        }
                    }
                } catch (final ExecutionException e) {
                    assert e.getCause() != null;
                    final String message = "failed to resolve host [" + hostname + "]";
                    logger.warn(message, e.getCause());
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                    // ignore
                }
            } else {
                logger.warn("timed out after [{}] resolving host [{}]", resolveTimeout, hostname);
            }
        }
        return Collections.unmodifiableList(transportAddresses);
    }
​
    @Override
    protected void doStart() {
        logger.debug("using max_concurrent_resolvers [{}], resolver timeout [{}]", concurrentConnects, resolveTimeout);
        final ThreadFactory threadFactory = EsExecutors.daemonThreadFactory(settings, "[unicast_configured_hosts_resolver]");
        executorService.set(EsExecutors.newScaling(nodeName + "/" + "unicast_configured_hosts_resolver",
            0, concurrentConnects, 60, TimeUnit.SECONDS, threadFactory, transportService.getThreadPool().getThreadContext()));
    }
​
    @Override
    protected void doStop() {
        ThreadPool.terminate(executorService.get(), 10, TimeUnit.SECONDS);
    }
​
    @Override
    protected void doClose() {
    }
​
    @Override
    public void resolveConfiguredHosts(Consumer<List<TransportAddress>> consumer) {
        if (lifecycle.started() == false) {
            logger.debug("resolveConfiguredHosts: lifecycle is {}, not proceeding", lifecycle);
            return;
        }
​
        if (resolveInProgress.compareAndSet(false, true)) {
            transportService.getThreadPool().generic().execute(new AbstractRunnable() {
                @Override
                public void onFailure(Exception e) {
                    logger.debug("failure when resolving unicast hosts list", e);
                }
​
                @Override
                protected void doRun() {
                    if (lifecycle.started() == false) {
                        logger.debug("resolveConfiguredHosts.doRun: lifecycle is {}, not proceeding", lifecycle);
                        return;
                    }
​
                    List<TransportAddress> providedAddresses
                        = hostsProvider.getSeedAddresses((hosts, limitPortCounts)
                        -> resolveHostsLists(executorService.get(), logger, hosts, limitPortCounts,
                        transportService, resolveTimeout));
​
                    consumer.accept(providedAddresses);
                }
​
                @Override
                public void onAfter() {
                    resolveInProgress.set(false);
                }
​
                @Override
                public String toString() {
                    return "SeedHostsResolver resolving unicast hosts list";
                }
            });
        }
    }
}