聊聊NacosNamingService的selectOneHealthyInstance

public class NacosNamingService implements NamingService {
    private static final String DEFAULT_PORT = "8080";
    private static final long DEFAULT_HEART_BEAT_INTERVAL = TimeUnit.SECONDS.toMillis(5);
​
    /**
     * Each Naming instance should have different namespace.
     */
    private String namespace;
​
    private String endpoint;
​
    private String serverList;
​
    private String cacheDir;
​
    private String logName;
​
    private HostReactor hostReactor;
​
    private BeatReactor beatReactor;
​
    private EventDispatcher eventDispatcher;
​
    private NamingProxy serverProxy;
​
    //......
​
    @Override
    public Instance selectOneHealthyInstance(String serviceName) throws NacosException {
        return selectOneHealthyInstance(serviceName, new ArrayList<String>());
    }
​
    @Override
    public Instance selectOneHealthyInstance(String serviceName, String groupName) throws NacosException {
        return selectOneHealthyInstance(serviceName, groupName, true);
    }
​
    @Override
    public Instance selectOneHealthyInstance(String serviceName, boolean subscribe) throws NacosException {
        return selectOneHealthyInstance(serviceName, new ArrayList<String>(), subscribe);
    }
​
    @Override
    public Instance selectOneHealthyInstance(String serviceName, String groupName, boolean subscribe) throws NacosException {
        return selectOneHealthyInstance(serviceName, groupName, new ArrayList<String>(), subscribe);
    }
​
    @Override
    public Instance selectOneHealthyInstance(String serviceName, List<String> clusters) throws NacosException {
        return selectOneHealthyInstance(serviceName, clusters, true);
    }
​
    @Override
    public Instance selectOneHealthyInstance(String serviceName, String groupName, List<String> clusters) throws NacosException {
        return selectOneHealthyInstance(serviceName, groupName, clusters, true);
    }
​
    @Override
    public Instance selectOneHealthyInstance(String serviceName, List<String> clusters, boolean subscribe)
        throws NacosException {
        return selectOneHealthyInstance(serviceName, Constants.DEFAULT_GROUP, clusters, subscribe);
    }
​
    @Override
    public Instance selectOneHealthyInstance(String serviceName, String groupName, List<String> clusters, boolean subscribe) throws NacosException {
​
        if (subscribe) {
            return Balancer.RandomByWeight.selectHost(
                hostReactor.getServiceInfo(NamingUtils.getGroupedName(serviceName, groupName), StringUtils.join(clusters, ",")));
        } else {
            return Balancer.RandomByWeight.selectHost(
                hostReactor.getServiceInfoDirectlyFromServer(NamingUtils.getGroupedName(serviceName, groupName), StringUtils.join(clusters, ",")));
        }
    }
​
    //......
}

public class Balancer {
​
    /**
     * report status to server
     */
    public final static List<String> UNCONSISTENT_SERVICE_WITH_ADDRESS_SERVER = new CopyOnWriteArrayList<String>();
​
    public static class RandomByWeight {
​
        public static List<Instance> selectAll(ServiceInfo serviceInfo) {
            List<Instance> hosts = serviceInfo.getHosts();
​
            if (CollectionUtils.isEmpty(hosts)) {
                throw new IllegalStateException("no host to srv for serviceInfo: " + serviceInfo.getName());
            }
​
            return hosts;
        }
​
        public static Instance selectHost(ServiceInfo dom) {
​
            List<Instance> hosts = selectAll(dom);
​
            if (CollectionUtils.isEmpty(hosts)) {
                throw new IllegalStateException("no host to srv for service: " + dom.getName());
            }
​
            return getHostByRandomWeight(hosts);
        }
    }
​
    /**
     * Return one host from the host list by random-weight.
     *
     * @param hosts The list of the host.
     * @return The random-weight result of the host
     */
    protected static Instance getHostByRandomWeight(List<Instance> hosts) {
        NAMING_LOGGER.debug("entry randomWithWeight");
        if (hosts == null || hosts.size() == 0) {
            NAMING_LOGGER.debug("hosts == null || hosts.size() == 0");
            return null;
        }
​
        Chooser<String, Instance> vipChooser = new Chooser<String, Instance>("www.taobao.com");
​
        NAMING_LOGGER.debug("new Chooser");
​
        List<Pair<Instance>> hostsWithWeight = new ArrayList<Pair<Instance>>();
        for (Instance host : hosts) {
            if (host.isHealthy()) {
                hostsWithWeight.add(new Pair<Instance>(host, host.getWeight()));
            }
        }
        NAMING_LOGGER.debug("for (Host host : hosts)");
        vipChooser.refresh(hostsWithWeight);
        NAMING_LOGGER.debug("vipChooser.refresh");
        return vipChooser.randomWithWeight();
    }
}

public class Chooser<K, T> {
​
    private K uniqueKey;
​
    private volatile Ref<T> ref;
​
    public T random() {
        List<T> items = ref.items;
        if (items.size() == 0) {
            return null;
        }
        if (items.size() == 1) {
            return items.get(0);
        }
        return items.get(ThreadLocalRandom.current().nextInt(items.size()));
    }
​
    public T randomWithWeight() {
        Ref<T> ref = this.ref;
        double random = ThreadLocalRandom.current().nextDouble(0, 1);
        int index = Arrays.binarySearch(ref.weights, random);
        if (index < 0) {
            index = -index - 1;
        } else {
            return ref.items.get(index);
        }
​
        if (index >= 0 && index < ref.weights.length) {
            if (random < ref.weights[index]) {
                return ref.items.get(index);
            }
        }
​
        /* This should never happen, but it ensures we will return a correct
         * object in case there is some floating point inequality problem
         * wrt the cumulative probabilities. */
        return ref.items.get(ref.items.size() - 1);
    }
​
    public Chooser(K uniqueKey) {
        this(uniqueKey, new ArrayList<Pair<T>>());
    }
​
    public Chooser(K uniqueKey, List<Pair<T>> pairs) {
        Ref<T> ref = new Ref<T>(pairs);
        ref.refresh();
        this.uniqueKey = uniqueKey;
        this.ref = ref;
    }
​
    public K getUniqueKey() {
        return uniqueKey;
    }
​
    public Ref<T> getRef() {
        return ref;
    }
​
    public void refresh(List<Pair<T>> itemsWithWeight) {
        Ref<T> newRef = new Ref<T>(itemsWithWeight);
        newRef.refresh();
        newRef.poller = this.ref.poller.refresh(newRef.items);
        this.ref = newRef;
    }
​
    //......
}

    public class Ref<T> {
        private List<Pair<T>> itemsWithWeight = new ArrayList<Pair<T>>();
        private List<T> items = new ArrayList<T>();
        private Poller<T> poller = new GenericPoller<T>(items);
        private double[] weights;
​
        @SuppressWarnings("unchecked")
        public Ref(List<Pair<T>> itemsWithWeight) {
            this.itemsWithWeight = itemsWithWeight;
        }
​
        public void refresh() {
            Double originWeightSum = (double) 0;
​
            for (Pair<T> item : itemsWithWeight) {
​
                double weight = item.weight();
                //ignore item which weight is zero.see test_randomWithWeight_weight0 in ChooserTest
                if (weight <= 0) {
                    continue;
                }
​
                items.add(item.item());
                if (Double.isInfinite(weight)) {
                    weight = 10000.0D;
                }
                if (Double.isNaN(weight)) {
                    weight = 1.0D;
                }
                originWeightSum += weight;
            }
​
            double[] exactWeights = new double[items.size()];
            int index = 0;
            for (Pair<T> item : itemsWithWeight) {
                double singleWeight = item.weight();
                //ignore item which weight is zero.see test_randomWithWeight_weight0 in ChooserTest
                if (singleWeight <= 0) {
                    continue;
                }
                exactWeights[index++] = singleWeight / originWeightSum;
            }
​
            weights = new double[items.size()];
            double randomRange = 0D;
            for (int i = 0; i < index; i++) {
                weights[i] = randomRange + exactWeights[i];
                randomRange += exactWeights[i];
            }
​
            double doublePrecisionDelta = 0.0001;
​
            if (index == 0 || (Math.abs(weights[index - 1] - 1) < doublePrecisionDelta)) {
                return;
            }
            throw new IllegalStateException("Cumulative Weight caculate wrong , the sum of probabilities does not equals 1.");
        }
​
        //......
    }