Dubbo-服务注册中心之AbstractRegistryFactory等源码
在上文中介绍了基础类AbstractRegistry类的解释，在本篇中将继续介绍该包下的其他类。
FailbackRegistry
该类继承了AbstractRegistry,AbstractRegistry中的注册订阅等方法，实际上就是一些内存缓存的变化，而真正的注册订阅的实现逻辑在FailbackRegistry实现，并且FailbackRegistry提供了失败重试的机制。
初始化
// Scheduled executor service
// 定时任务执行器
private final ScheduledExecutorService retryExecutor = Executors.newScheduledThreadPool(1, new NamedThreadFactory("DubboRegistryFailedRetryTimer", true));
// Timer for failure retry, regular check if there is a request for failure, and if there is, an unlimited retry
// 失败重试定时器，定时去检查是否有请求失败的，如有，无限次重试。
private final ScheduledFuture<?> retryFuture;
// 注册失败的URL集合
private final Set<URL> failedRegistered = new ConcurrentHashSet<URL>();
// 取消注册失败的URL集合
private final Set<URL> failedUnregistered = new ConcurrentHashSet<URL>();
// 订阅失败的监听器集合
private final ConcurrentMap<URL, Set<NotifyListener>> failedSubscribed = new ConcurrentHashMap<URL, Set<NotifyListener>>();
// 取消订阅失败的监听器集合
private final ConcurrentMap<URL, Set<NotifyListener>> failedUnsubscribed = new ConcurrentHashMap<URL, Set<NotifyListener>>();
// 通知失败的URL集合
private final ConcurrentMap<URL, Map<NotifyListener, List<URL>>> failedNotified = new ConcurrentHashMap<URL, Map<NotifyListener, List<URL>>>();
/**
* The time in milliseconds the retryExecutor will wait
*/
// 重试频率
private final int retryPeriod;
构造函数
public FailbackRegistry(URL url) {
super(url);
// 从url中读取重试频率，如果为空，则默认5000ms
this.retryPeriod = url.getParameter(Constants.REGISTRY_RETRY_PERIOD_KEY, Constants.DEFAULT_REGISTRY_RETRY_PERIOD);
// 创建失败重试定时器
this.retryFuture = retryExecutor.scheduleWithFixedDelay(new Runnable() {
@Override
public void run() {
// Check and connect to the registry
try {
//重试
retry();
} catch (Throwable t) { // Defensive fault tolerance
logger.error("Unexpected error occur at failed retry, cause: " + t.getMessage(), t);
}
}
}, retryPeriod, retryPeriod, TimeUnit.MILLISECONDS);
}
构造函数主要是创建了失败重试的定时器，重试频率从URL取，如果没有设置，则默认为5000ms。
在该类中对注册、取消注册、订阅、取消订阅进行了重写操作，代码逻辑相对简单。
@Override
public void register(URL url) {
super.register(url);
//首先从失败的缓存中删除该url
failedRegistered.remove(url);
failedUnregistered.remove(url);
try {
// Sending a registration request to the server side
// 向注册中心发送一个注册请求
doRegister(url);
} catch (Exception e) {
Throwable t = e;
// If the startup detection is opened, the Exception is thrown directly.
// 如果开启了启动时检测，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);
}
// Record a failed registration request to a failed list, retry regularly
// 把这个注册失败的url放入缓存，并且定时重试。
failedRegistered.add(url);
}
}
在注册中它会失败的注册缓存和失败的未注册缓存集合中移除该URL,然后向注册中心执行注册。
AbstractRegistryFactory
该类实现了RegistryFactory接口，抽象了createRegistry方法，它实现了Registry的容器。
初始化
private static final ReentrantLock LOCK = new ReentrantLock();
// Registry Collection Map<RegistryAddress, Registry>
// Registry 集合
private static final Map<String, Registry> REGISTRIES = new ConcurrentHashMap<String, Registry>();
销毁所有的Registry对象,并清理缓存数据
public static Collection<Registry> getRegistries() {
return Collections.unmodifiableCollection(REGISTRIES.values());
}
public static void destroyAll() {
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Close all registries " + getRegistries());
}
// Lock up the registry shutdown process
// 获得锁
LOCK.lock();
try {
for (Registry registry : getRegistries()) {
try {
// 销毁
registry.destroy();
} catch (Throwable e) {
LOGGER.error(e.getMessage(), e);
}
}
// 清空缓存
REGISTRIES.clear();
} finally {
// Release the lock
// 释放锁
LOCK.unlock();
}
}
该方法是实现了Registry接口的方法，这里最要注意的是createRegistry,因为AbstractRegistryFfactory本身就是抽象类，而createRegistry也是抽象方法，为了让子类只要关注该方法，比如说redis实现的注册中心和zookeeper实现的注册中心创建方式肯定不同，而他们相同的一些操作都已经在AbstractRegistryFactory中实现，所以只要关注且实现该抽象方法即可。
@Override
public Registry getRegistry(URL url) {
// 修改url
url = url.setPath(RegistryService.class.getName())
.addParameter(Constants.INTERFACE_KEY, RegistryService.class.getName())
.removeParameters(Constants.EXPORT_KEY, Constants.REFER_KEY);
// 计算key值
String key = url.toServiceString();
// Lock the registry access process to ensure a single instance of the registry
// 获得锁
LOCK.lock();
try {
Registry registry = REGISTRIES.get(key);
if (registry != null) {
return registry;
}
// 创建Registry对象
registry = createRegistry(url);
if (registry == null) {
throw new IllegalStateException("Can not create registry " + url);
}
// 添加到缓存。
REGISTRIES.put(key, registry);
return registry;
} finally {
// Release the lock
// 释放锁
LOCK.unlock();
}
}
