Dubbo源码解析之registry注册中心
阅读须知
- dubbo版本：2.6.0
- spring版本：4.3.8
- 文章中使用/* */注释的方法会做深入分析
正文
注册中心是Dubbo的重要组成部分，主要用于服务的注册与发现，我们可以选择Redis、数据库、Zookeeper作为Dubbo的注册中心，Dubbo推荐用户使用Zookeeper作为注册中心，
在provider和consumer的初始化过程中，我们看到了dubbo通过调用RegistryFactory的getRegistry方法来获取注册中心实例，我们就以这个方法作为入口来分析注册中心的相关流程：
AbstractRegistryFactory：
@Override public Registry getRegistry(URL url) { url = URLBuilder.from(url) .setPath(RegistryService.class.getName()) .addParameter(Constants.INTERFACE_KEY, RegistryService.class.getName()) .removeParameters(Constants.EXPORT_KEY, Constants.REFER_KEY) .build(); String key = url.toServiceStringWithoutResolving(); // Lock the registry access process to ensure a single instance of the registry //锁定注册中心的访问过程以确保注册中心的单个实例 LOCK.lock(); try { Registry registry = REGISTRIES.get(key);//缓存 if (registry != null) { return registry; } //create registry by spi/ioc //创建注册中心实例 registry = createRegistry(url); if (registry == null) { throw new IllegalStateException("Can not create registry " + url); } REGISTRIES.put(key, registry); return registry; } finally { // Release the lock LOCK.unlock(); } }
ZookeeperRegistryFactory：
@Override public Registry createRegistry(URL url) { //创建zookeeperRegistery实例 return new ZookeeperRegistry(url, zookeeperTransporter); }
ZookeeperRegistry：
public ZookeeperRegistry(URL url, ZookeeperTransporter zookeeperTransporter) { super(url); //构造父类构造方法 if (url.isAnyHost()) { throw new IllegalStateException("registry address == null"); } String group = url.getParameter(Constants.GROUP_KEY, DEFAULT_ROOT); if (!group.startsWith(Constants.PATH_SEPARATOR)) { group = Constants.PATH_SEPARATOR + group; } this.root = group; //连接zookeeper zkClient = zookeeperTransporter.connect(url); //添加监听器 zkClient.addStateListener(state -> { if (state == StateListener.RECONNECTED) { try { //如果监听到的状态是重连，做恢复操作。 recover(); } catch (Exception e) { logger.error(e.getMessage(), e); } } }); }
FailbackRegistry
public FailbackRegistry(URL url) { //调用父类构造方法 super(url); //重试间隔，默认5000ms this.retryPeriod = url.getParameter(Constants.REGISTRY_RETRY_PERIOD_KEY, Constants.DEFAULT_REGISTRY_RETRY_PERIOD); // since the retry task will not be very much. 128 ticks is enough. retryTimer = new HashedWheelTimer(new NamedThreadFactory("DubboRegistryRetryTimer", true), retryPeriod, TimeUnit.MILLISECONDS, 128); }
AbstractRegistry
public AbstractRegistry(URL url) { setUrl(url); // Start file save timer //是否同步保存文件，默认为false syncSaveFile = url.getParameter(Constants.REGISTRY_FILESAVE_SYNC_KEY, false); //配置缓存文件，默认在用户目录 /.dubbo文件夹下 String filename = url.getParameter(Constants.FILE_KEY, System.getProperty("user.home") + "/.dubbo/dubbo-registry-" + url.getParameter(Constants.APPLICATION_KEY) + "-" + url.getAddress() + ".cache"); File file = null; if (ConfigUtils.isNotEmpty(filename)) { file = new File(filename); if (!file.exists() && file.getParentFile() != null && !file.getParentFile().exists()) { if (!file.getParentFile().mkdirs()) { throw new IllegalArgumentException("Invalid registry cache file " + file + ", cause: Failed to create directory " + file.getParentFile() + "!"); } } } this.file = file; // When starting the subscription center, // we need to read the local cache file for future Registry fault tolerance processing. loadProperties();//将缓存文件加载为properties notify(url.getBackupUrls());//通知更新配置 }
这里提到了缓存文件，
简单来说它就是用来做容灾的，consumer从注册中心订阅了provider等信息后会缓存到本地文件中，
这样当注册中心不可用时，consumer启动时就可以加载这个缓存文件里面的内容与provider进行交互，
这样就可以不依赖注册中心，但是无法获取到新的provider变更通知，
所以如果provider信息在注册中心不可用这段时间发生了很大变化，那就很可能会出现服务无法调用的情况，在2.5.7（记得是这个版本）版本之前，dubbo有一个bug，如果启动时注册中心连接不上，启动程序会hang住，无法启动，所以在2.5.7版本之前这个文件是没用的，在2.5.7版本进行了修复。下面我们来看FailbackRegistry用HashedWheelTimer重试什么东西：
public HashedWheelTimer( ThreadFactory threadFactory, long tickDuration, TimeUnit unit, int ticksPerWheel, long maxPendingTimeouts) { if (threadFactory == null) { throw new NullPointerException("threadFactory"); } if (unit == null) { throw new NullPointerException("unit"); } if (tickDuration <= 0) { throw new IllegalArgumentException("tickDuration must be greater than 0: " + tickDuration); } if (ticksPerWheel <= 0) { throw new IllegalArgumentException("ticksPerWheel must be greater than 0: " + ticksPerWheel); } // Normalize ticksPerWheel to power of two and initialize the wheel. wheel = createWheel(ticksPerWheel); mask = wheel.length - 1; // Convert tickDuration to nanos. this.tickDuration = unit.toNanos(tickDuration); // Prevent overflow. if (this.tickDuration >= Long.MAX_VALUE / wheel.length) { throw new IllegalArgumentException(String.format( "tickDuration: %d (expected: 0 < tickDuration in nanos < %d", tickDuration, Long.MAX_VALUE / wheel.length)); } workerThread = threadFactory.newThread(worker); this.maxPendingTimeouts = maxPendingTimeouts; if (INSTANCE_COUNTER.incrementAndGet() > INSTANCE_COUNT_LIMIT && WARNED_TOO_MANY_INSTANCES.compareAndSet(false, true)) { reportTooManyInstances(); } }
我们看到，重试就是对注册、订阅等各个失败的操作进行重试，dubbo会在这些动作失败时将失败的记录存入集合或map中，这里会取出这些记录进行重试。
下面我们来看zookeeper的链接，可以选择使用ZkClient或curator来连接zookeeper，默认为ZkClient：
public ZookeeperClient connect(URL url) {
/* 构建ZkclientZookeeperClient */
return new ZkclientZookeeperClient(url);
}
ZkclientZookeeperClient
public ZkclientZookeeperClient(URL url) {
super(url);
/* 构建ZkClientWrapper，可以在连接超时后自动监控连接的状态 */
client = new ZkClientWrapper(url.getBackupAddress(), 30000);
// 添加监听器，用于连接状态变更通知监听器
client.addListener(new IZkStateListener() {
public void handleStateChanged(KeeperState state) throws Exception {
ZkclientZookeeperClient.this.state = state;
if (state == KeeperState.Disconnected) {
stateChanged(StateListener.DISCONNECTED);
} else if (state == KeeperState.SyncConnected) {
stateChanged(StateListener.CONNECTED);
}
}
public void handleNewSession() throws Exception {
stateChanged(StateListener.RECONNECTED);
}
});
client.start(); /* 开启线程，连接zookeeper */
}
ZkClientWrapper
public ZkClientWrapper(final String serverAddr, long timeout) {
this.timeout = timeout;
// 创建任务创建ZkClient
listenableFutureTask = ListenableFutureTask.create(new Callable() {
@Override
public ZkClient call() throws Exception {
return new ZkClient(serverAddr, Integer.MAX_VALUE);
}
});
}
ZkClientWrapper
public void start() { if (!started) { Thread connectThread = new Thread(listenableFutureTask); connectThread.setName("DubboZkclientConnector"); connectThread.setDaemon(true); connectThread.start(); // 创建线程执行创建ZkClient任务 try { client = listenableFutureTask.get(timeout, TimeUnit.MILLISECONDS); } catch (Throwable t) { logger.error("Timeout! zookeeper server can not be connected in : " + timeout + "ms!", t); } started = true; } else { logger.warn("Zkclient has already been started!"); } }
创建ZkClient之后接下来添加添加了一个连接状态变更监听器，目的是在重连时做恢复操作：
FailbackRegistry：
protected void recover() throws Exception {
Set recoverRegistered = new HashSet(getRegistered());
if (!recoverRegistered.isEmpty()) {
if (logger.isInfoEnabled()) {
logger.info("Recover register url " + recoverRegistered);
}
for (URL url : recoverRegistered) {
failedRegistered.add(url); // 将注册相关信息添加到失败注册集合中
}
}
Map> recoverSubscribed = new HashMap>(getSubscribed());
if (!recoverSubscribed.isEmpty()) {
if (logger.isInfoEnabled()) {
logger.info("Recover subscribe url " + recoverSubscribed.keySet());
}
for (Map.Entry> entry : recoverSubscribed.entrySet()) {
URL url = entry.getKey();
for (NotifyListener listener : entry.getValue()) {
// 将订阅相关信息添加到失败订阅map中
addFailedSubscribed(url, listener);
}
}
}
}
我们看到，恢复操作其实就是将注册和订阅的信息保存起来，我们之前看到的重试流程会拉取这些信息进行重试。接下来就是将服务信息注册到注册中心：
FailbackRegistry
public void register(URL url) { if (destroyed.get()){ return; } super.register(url); // 添加到已注册服务集合中 failedRegistered.remove(url); // 从失败的注册集合中移除 failedUnregistered.remove(url); // 从失败的注销集合中移除 try { doRegister(url); /* 发起注册请求 */ } catch (Exception e) { Throwable t = e; // 如果启动检测被打开，则直接抛出异常 boolean check = getUrl().getParameter(Constants.CHECK_KEY, true) && url.getParameter(Constants.CHECK_KEY, true) && !Constants.CONSUMER_PROTOCOL.equals(url.getProtocol()); boolean skipFailback = t instanceof SkipFailbackWrapperException; if (check || skipFailback) { if (skipFailback) { t = t.getCause(); } throw new IllegalStateException("Failed to register " + url + " to registry " + getUrl().getAddress() + ", cause: " + t.getMessage(), t); } else { logger.error("Failed to register " + url + ", waiting for retry, cause: " + t.getMessage(), t); } // 将失败的注册请求记录到失败的列表中，定期重试 failedRegistered.add(url); } }
ZookeeperRegistry
protected void doRegister(URL url) {
try {
/* 创建zookeeper节点 默认为临时节点*/
zkClient.create(toUrlPath(url), url.getParameter(Constants.DYNAMIC_KEY, true));
} catch (Throwable e) {
throw new RpcException("Failed to register " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e);
}
}
AbstractZookeeperClient
public void create(String path, boolean ephemeral) {
int i = path.lastIndexOf('/');
if (i > 0) {
String parentPath = path.substring(0, i);
if (!checkExists(parentPath)) {
// 递归创建父节点
create(parentPath, false);
}
}
if (ephemeral) {
createEphemeral(path); /* 创建临时节点 */
} else {
createPersistent(path); /* 创建持久节点 */
}
}
ZkclientZookeeperClient：
public void createEphemeral(String path) {
try {
/* 创建临时节点 */
client.createEphemeral(path);
} catch (ZkNodeExistsException e) {
}
}ZkClientWrapper：
public void createEphemeral(String path) {
Assert.notNull(client, new IllegalStateException("Zookeeper is not connected yet!"));
// 调用ZkClient的createEphemeral方法创建临时节点
client.createEphemeral(path);
}
ZkclientZookeeperClient：
public void createPersistent(String path) {
try {
/* 创建持久节点 */
client.createPersistent(path);
} catch (ZkNodeExistsException e) {
}
}
ZkClientWrapper：
public void createPersistent(String path) {
Assert.notNull(client, new IllegalStateException("Zookeeper is not connected yet!"));
// 调用ZkClient的createPersistent方法创建临时节点
client.createPersistent(path, true);
}
在注册中心创建完成服务信息节点之后是订阅操作：
FailbackRegistry
posted on 2019-04-23 22:39 shoshana~ 阅读( ...) 评论( ...) 编辑 收藏