Nacos - HostReactor的创建

Nacos - NacosNamingService初始化中提到NacosNamingService初始化会初始化EventDispatcher、NamingProxy、BeatReactor、HostReactor。其中EventDispatcher已经说了，NamingProxy的定时任务主要是默认每30毫秒更新服务器地址、默认每5毫秒登陆获取token等信息，这里过了。BeatReactor初始化的时候并没有开启定时任务，后面来说，那只剩下HostReactor了。
我们看看他的构造函数，会创建一个FailoverReactor和PushReceiver对象。

public HostReactor(EventDispatcher eventDispatcher, NamingProxy serverProxy, BeatReactor beatReactor,
        String cacheDir, boolean loadCacheAtStart, int pollingThreadCount) {
    // 其他略
    this.failoverReactor = new FailoverReactor(this, cacheDir);
    this.pushReceiver = new PushReceiver(this);
}

FailoverReactor

FailoverReactor的构造函数，会调用他的init方法：

public FailoverReactor(HostReactor hostReactor, String cacheDir) {
    //其他略
    this.init();
}

在init里会有三个任务：

1. FailoverReactor.SwitchRefresher,默认每5秒检测是否开启故障转移，如果开启，则把文件数据读入serviceMap。
2. FailoverReactor.DiskFileWriter,默认每天把服务信息写入本地。
3. 创建10秒后调用DiskFileWriter#run，检测本地缓存文件，如果没有则创建缓存文件。

public void init() {
        
    executorService.scheduleWithFixedDelay(new SwitchRefresher(), 0L, 5000L, TimeUnit.MILLISECONDS);
    
    executorService.scheduleWithFixedDelay(new DiskFileWriter(), 30, DAY_PERIOD_MINUTES, TimeUnit.MINUTES);
    
    // backup file on startup if failover directory is empty.
    executorService.schedule(new Runnable() {
        //其他略
    }, 10000L, TimeUnit.MILLISECONDS);
}

FailoverReactor.SwitchRefresher,默认每5秒检测是否开启故障转移，如果开启，则把文件数据读入serviceMap。

class SwitchRefresher implements Runnable {       
    long lastModifiedMillis = 0L;    
    @Override
    public void run() {
        try {
            // 其他略    
            switchParams.put("failover-mode", "true");
            NAMING_LOGGER.info("failover-mode is on");
            // 故障转移的时候调用FailoverFileReader#run
            new FailoverFileReader().run();
        } catch (Throwable e) {
            NAMING_LOGGER.error("[NA] failed to read failover switch.", e);
        }
    }
}

class FailoverFileReader implements Runnable {
    
    @Override
    public void run() {
        Map<String, ServiceInfo> domMap = new HashMap<String, ServiceInfo>(16);
        
        BufferedReader reader = null;
        try {
            // 其他略
            // 读取文件信息，赋值给dom，存入domMap
            for (File file : files) {
                // 其他略
                ServiceInfo dom = new ServiceInfo(file.getName());                
                // 其他略
                dom = JacksonUtils.toObj(json, ServiceInfo.class);            
                if (!CollectionUtils.isEmpty(dom.getHosts())) {
                    domMap.put(dom.getKey(), dom);
                }
            }
        } catch (Exception e) {
            NAMING_LOGGER.error("[NA] failed to read cache file", e);
        }
        // domMap的值赋值给serviceMap
        if (domMap.size() > 0) {
            serviceMap = domMap;
        }
    }
}

PushReceiver

PushReceiver实现了Runnable接口，在构造函数中把自己放入了线程池。

public PushReceiver(HostReactor hostReactor) {
    try {
        //其他略
        this.executorService.execute(this);
    } catch (Exception e) {
        NAMING_LOGGER.error("[NA] init udp socket failed", e);
    }
}

在run中，通过while一直监听UDP数据，并根据不同的type进行处理数据，处理后响应请求。

@Override
public void run() {
    while (!closed) {
        try {
            
            // byte[] is initialized with 0 full filled by default
            byte[] buffer = new byte[UDP_MSS];
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
            // 获取UDP数据
            udpSocket.receive(packet);
            
            String json = new String(IoUtils.tryDecompress(packet.getData()), UTF_8).trim();
            NAMING_LOGGER.info("received push data: " + json + " from " + packet.getAddress().toString());
            
            PushPacket pushPacket = JacksonUtils.toObj(json, PushPacket.class);
            String ack;
            // 根据不同的type进行处理数据
            if ("dom".equals(pushPacket.type) || "service".equals(pushPacket.type)) {
                hostReactor.processServiceJson(pushPacket.data);
                
                // send ack to server
                ack = "{\"type\": \"push-ack\"" + ", \"lastRefTime\":\"" + pushPacket.lastRefTime + "\", \"data\":"
                        + "\"\"}";
            } else if ("dump".equals(pushPacket.type)) {
                // dump data to server
                ack = "{\"type\": \"dump-ack\"" + ", \"lastRefTime\": \"" + pushPacket.lastRefTime + "\", \"data\":"
                        + "\"" + StringUtils.escapeJavaScript(JacksonUtils.toJson(hostReactor.getServiceInfoMap()))
                        + "\"}";
            } else {
                // do nothing send ack only
                ack = "{\"type\": \"unknown-ack\"" + ", \"lastRefTime\":\"" + pushPacket.lastRefTime
                        + "\", \"data\":" + "\"\"}";
            }
            // 响应请求
            udpSocket.send(new DatagramPacket(ack.getBytes(UTF_8), ack.getBytes(UTF_8).length,
                    packet.getSocketAddress()));
        } catch (Exception e) {
            NAMING_LOGGER.error("[NA] error while receiving push data", e);
        }
    }
}

总结

HostReactor的创建任务包括每5秒检测是否开启故障转移，如果开启，则把文件数据读入serviceMap、每天把服务信息写入本地、检测本地缓存文件，如果没有则创建缓存文件、监听UDP请求。