nacos的DistroMapper有什么作用

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序

本文主要研究一下nacos的DistroMapper

ServerChangeListener

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/cluster/servers/ServerChangeListener.java

public interface ServerChangeListener {    /**     * If member list changed, this method is invoked.     *     * @param servers servers after change     */    void onChangeServerList(List servers);    /**     * If reachable member list changed, this method is invoked.     *     * @param healthyServer reachable servers after change     */    void onChangeHealthyServerList(List healthyServer);}

• ServerChangeListener定义了onChangeServerList、onChangeHealthyServerList方法

DistroMapper

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/core/DistroMapper.java

@Component("distroMapper")public class DistroMapper implements ServerChangeListener {    private List healthyList = new ArrayList<>();    public List getHealthyList() {        return healthyList;    }    @Autowired    private SwitchDomain switchDomain;    @Autowired    private ServerListManager serverListManager;    /**     * init server list     */    @PostConstruct    public void init() {        serverListManager.listen(this);    }    public boolean responsible(Cluster cluster, Instance instance) {        return switchDomain.isHealthCheckEnabled(cluster.getServiceName())            && !cluster.getHealthCheckTask().isCancelled()            && responsible(cluster.getServiceName())            && cluster.contains(instance);    }    public boolean responsible(String serviceName) {        if (!switchDomain.isDistroEnabled() || SystemUtils.STANDALONE_MODE) {            return true;        }        if (CollectionUtils.isEmpty(healthyList)) {            // means distro config is not ready yet            return false;        }        int index = healthyList.indexOf(NetUtils.localServer());        int lastIndex = healthyList.lastIndexOf(NetUtils.localServer());        if (lastIndex < 0 || index < 0) {            return true;        }        int target = distroHash(serviceName) % healthyList.size();        return target >= index && target <= lastIndex;    }    public String mapSrv(String serviceName) {        if (CollectionUtils.isEmpty(healthyList) || !switchDomain.isDistroEnabled()) {            return NetUtils.localServer();        }        try {            return healthyList.get(distroHash(serviceName) % healthyList.size());        } catch (Exception e) {            Loggers.SRV_LOG.warn("distro mapper failed, return localhost: " + NetUtils.localServer(), e);            return NetUtils.localServer();        }    }    public int distroHash(String serviceName) {        return Math.abs(serviceName.hashCode() % Integer.MAX_VALUE);    }    @Override    public void onChangeServerList(List latestMembers) {    }    @Override    public void onChangeHealthyServerList(List latestReachableMembers) {        List newHealthyList = new ArrayList<>();        for (Server server : latestReachableMembers) {            newHealthyList.add(server.getKey());        }        healthyList = newHealthyList;    }}

• DistroMapper实现了ServerChangeListener接口，其onChangeHealthyServerList方法会更新healthyList

• 它还提供了responsible方法，该方法在switchDomain.isHealthCheckEnabled以及cluster.getHealthCheckTask()不是cancelled的情况下会执行responsible，该方法会调用distroHash来计算hash值

• 它还提供了mapSrv方法，也是通过distroHash计算hash然后与healthyList的大小取余，最后返回server的key

小结

ServerChangeListener定义了onChangeServerList、onChangeHealthyServerList方法；DistroMapper实现了ServerChangeListener接口，其onChangeHealthyServerList方法会更新healthyList；DistroMapper还提供了responsible方法及mapSrv方法

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