二 nacos注册中心源码解析--服务发现

最新推荐文章于 2024-11-14 16:47:58 发布

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本文详细解读了Nacos客户端如何通过NacosNamingService获取服务实例列表，涉及HostReactor的getServiceInfo、getServiceInfo0和updateService方法，以及定时任务的调度过程。重点展示了实例列表的本地缓存管理和远程API拉取策略。

一核心原理图

在这里插入图片描述

二源码解析

2.1 客户端获取查询实例列表

通过服务名称获取和当前服务名称相关的服务实例
com.alibaba.nacos.client.naming.NacosNamingService#getAllInstances

public List<Instance> selectInstances(String serviceName, String groupName, List<String> clusters, boolean healthy,
            boolean subscribe) throws NacosException {
        
        ServiceInfo serviceInfo;
        if (subscribe) {
        	// 通过hostReactor 获取应用实例
            serviceInfo = hostReactor.getServiceInfo(NamingUtils.getGroupedName(serviceName, groupName),
                    StringUtils.join(clusters, ","));
        } else {
            serviceInfo = hostReactor
                    .getServiceInfoDirectlyFromServer(NamingUtils.getGroupedName(serviceName, groupName),
                            StringUtils.join(clusters, ","));
        }
        return selectInstances(serviceInfo, healthy);
    }

获取服务信息
com.alibaba.nacos.client.naming.core.HostReactor#getServiceInfo

public ServiceInfo getServiceInfo(final String serviceName, final String clusters) {
    
    NAMING_LOGGER.debug("failover-mode: " + failoverReactor.isFailoverSwitch());
    String key = ServiceInfo.getKey(serviceName, clusters);
    if (failoverReactor.isFailoverSwitch()) {
        return failoverReactor.getService(key);
    }
    // 从缓存中获取实例信息
    ServiceInfo serviceObj = getServiceInfo0(serviceName, clusters);
    // 第一次获取是空的
    if (null == serviceObj) {
        serviceObj = new ServiceInfo(serviceName, clusters);
        
        serviceInfoMap.put(serviceObj.getKey(), serviceObj);
        
        updatingMap.put(serviceName, new Object());
        // 远程调用API 拉取是实例列表 更新服务列表
        updateServiceNow(serviceName, clusters);
        updatingMap.remove(serviceName);
        
    } else if (updatingMap.containsKey(serviceName)) {
        
        if (UPDATE_HOLD_INTERVAL > 0) {
            // hold a moment waiting for update finish
            synchronized (serviceObj) {
                try {
                    serviceObj.wait(UPDATE_HOLD_INTERVAL);
                } catch (InterruptedException e) {
                    NAMING_LOGGER
                            .error("[getServiceInfo] serviceName:" + serviceName + ", clusters:" + clusters, e);
                }
            }
        }
    }
    // 开启定时更新实例列表
    scheduleUpdateIfAbsent(serviceName, clusters);
    
    return serviceInfoMap.get(serviceObj.getKey());
}

获取客户端的服务实例缓存信息
com.alibaba.nacos.client.naming.core.HostReactor#getServiceInfo0

private ServiceInfo getServiceInfo0(String serviceName, String clusters) {
        
        String key = ServiceInfo.getKey(serviceName, clusters);
        
        return serviceInfoMap.get(key);
    }

获取服务端最新的实例，将获取的实例列表放入serviceInfoMap
com.alibaba.nacos.client.naming.core.HostReactor#updateService

public void updateService(String serviceName, String clusters) throws NacosException {
    ServiceInfo oldService = getServiceInfo0(serviceName, clusters);
    try {
        // 查询实例列表API
        String result = serverProxy.queryList(serviceName, clusters, pushReceiver.getUdpPort(), false);
        
        if (StringUtils.isNotEmpty(result)) {
            // 将获取的实例列表放入serviceInfoMap
            processServiceJson(result);
        }
    } finally {
        if (oldService != null) {
            synchronized (oldService) {
                oldService.notifyAll();
            }
        }
    }
}

2.2 定时获取最新实例列表，更新客户端的服务缓存

在查询服务调用 getServiceInfo 方法的代码中，会开启一个定时任务，这个任务会在默认在1s之后开
始执行。而任务的具体实现是一个UpdateTask

public void scheduleUpdateIfAbsent(String serviceName, String clusters) {
        if (futureMap.get(ServiceInfo.getKey(serviceName, clusters)) != null) {
            return;
        }
        
        synchronized (futureMap) {
            if (futureMap.get(ServiceInfo.getKey(serviceName, clusters)) != null) {
                return;
            }
            
            ScheduledFuture<?> future = addTask(new UpdateTask(serviceName, clusters));
            futureMap.put(ServiceInfo.getKey(serviceName, clusters), future);
        }
    }

定时获取服务端最新实例数据并更新到本地缓存
com.alibaba.nacos.client.naming.core.HostReactor.UpdateTask#run

 @Override
public void run() {
    long delayTime = DEFAULT_DELAY;
    
    try {
        ServiceInfo serviceObj = serviceInfoMap.get(ServiceInfo.getKey(serviceName, clusters));
        
        if (serviceObj == null) {
            // 获取最新的实例列表,并更新serviceInfoMap
            updateService(serviceName, clusters);
            return;
        }
        
        if (serviceObj.getLastRefTime() <= lastRefTime) {
            updateService(serviceName, clusters);
            serviceObj = serviceInfoMap.get(ServiceInfo.getKey(serviceName, clusters));
        } else {
            // if serviceName already updated by push, we should not override it
            // since the push data may be different from pull through force push
            refreshOnly(serviceName, clusters);
        }
        
        lastRefTime = serviceObj.getLastRefTime();
        
        if (!notifier.isSubscribed(serviceName, clusters) && !futureMap
                .containsKey(ServiceInfo.getKey(serviceName, clusters))) {
            // abort the update task
            NAMING_LOGGER.info("update task is stopped, service:" + serviceName + ", clusters:" + clusters);
            return;
        }
        if (CollectionUtils.isEmpty(serviceObj.getHosts())) {
            incFailCount();
            return;
        }
        delayTime = serviceObj.getCacheMillis();
        resetFailCount();
    } catch (Throwable e) {
        incFailCount();
        NAMING_LOGGER.warn("[NA] failed to update serviceName: " + serviceName, e);
    } finally {
        // 嵌套调度
        executor.schedule(this, Math.min(delayTime << failCount, DEFAULT_DELAY * 60), TimeUnit.MILLISECONDS);
    }
}