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：
- 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。
- FailoverReactor.DiskFileWriter,默认每天把服务信息写入本地。
- 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 domMap = new HashMap(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。