现象
使用dubbo的开发者对dubbo泛化调用肯定不陌生。我们在定时任务管理场景中使用dubbo的泛化调用（泛化调用dubbo接口）。一次，同事在测试环境配置定时任务 10s执行一次，但是配置的接口并没有提供者。过不多久，zookeeper上就有了上万个消费者节点。
官方dubbo泛化调用的示例是这样的：
ReferenceConfig获取"服务引用"的时候先取已经实例化的"服务引用"，如果没有实例化过则会调用init来实例化"服务引用"。实例化"服务引用"过程默认要check提供者是否存在，不存在则抛异常导致实例化失败(此时已经在zookeeper上创建了消费者节点)。下一次通过ReferenceConfig获取"服务引用"又会失败(也会创建消费者节点，消费者节点上会带上时间戳所以每次都会创建新的节点)。如此反复，就会无穷尽的创建zk节点。 看一下ReferenceConfig获取"服务引用"的源码（关键位置笔者加了注视）：
public class ReferenceConfig<T> extends AbstractReferenceConfig {
/**
* The interface proxy reference
*/
private transient volatile T ref;
...
public synchronized T get() {
checkAndUpdateSubConfigs();
if (destroyed) {
throw new IllegalStateException("The invoker of ReferenceConfig(" + url + ") has already destroyed!");
}
// 笔者注： 是否已经实例化了"服务引用"， 没有则调用init实例化"服务引用"
if (ref == null) {
init();
}
return ref;
}
//笔者注：初始化"服务引用"
private void init() {
if (initialized) {
return;
}
checkStubAndLocal(interfaceClass);
checkMock(interfaceClass);
Map<String, String> map = new HashMap<String, String>();
map.put(SIDE_KEY, CONSUMER_SIDE);
//笔者注：这里拼接上了"时间戳"的参数
appendRuntimeParameters(map);
if (!isGeneric()) {
String revision = Version.getVersion(interfaceClass, version);
if (revision != null && revision.length() > 0) {
map.put(REVISION_KEY, revision);
}
String[] methods = Wrapper.getWrapper(interfaceClass).getMethodNames();
if (methods.length == 0) {
logger.warn("No method found in service interface " + interfaceClass.getName());
map.put(METHODS_KEY, ANY_VALUE);
} else {
map.put(METHODS_KEY, StringUtils.join(new HashSet<String>(Arrays.asList(methods)), COMMA_SEPARATOR));
}
}
map.put(INTERFACE_KEY, interfaceName);
appendParameters(map, metrics);
appendParameters(map, application);
appendParameters(map, module);
// remove 'default.' prefix for configs from ConsumerConfig
// appendParameters(map, consumer, Constants.DEFAULT_KEY);
appendParameters(map, consumer);
appendParameters(map, this);
Map<String, Object> attributes = null;
if (CollectionUtils.isNotEmpty(methods)) {
attributes = new HashMap<String, Object>();
for (MethodConfig methodConfig : methods) {
appendParameters(map, methodConfig, methodConfig.getName());
String retryKey = methodConfig.getName() + ".retry";
if (map.containsKey(retryKey)) {
String retryValue = map.remove(retryKey);
if ("false".equals(retryValue)) {
map.put(methodConfig.getName() + ".retries", "0");
}
}
attributes.put(methodConfig.getName(), convertMethodConfig2AyncInfo(methodConfig));
}
}
String hostToRegistry = ConfigUtils.getSystemProperty(DUBBO_IP_TO_REGISTRY);
if (StringUtils.isEmpty(hostToRegistry)) {
hostToRegistry = NetUtils.getLocalHost();
} else if (isInvalidLocalHost(hostToRegistry)) {
throw new IllegalArgumentException("Specified invalid registry ip from property:" + DUBBO_IP_TO_REGISTRY + ", value:" + hostToRegistry);
}
map.put(REGISTER_IP_KEY, hostToRegistry);
// 笔者注: createProxy抛异常的化 ref就没有设置值，仍然为空
ref = createProxy(map);
String serviceKey = URL.buildKey(interfaceName, group, version);
ApplicationModel.initConsumerModel(serviceKey, buildConsumerModel(serviceKey, attributes));
initialized = true;
}
//笔者注： 创建"服务引用" 实例，
//(1)先在zk上创建一个消费者节点
//(2)校验服务是否可用(如果配置了需要校验)，不可用抛异常
//(3)创建一个代理对象
private T createProxy(Map<String, String> map) {
if (shouldJvmRefer(map)) {
URL url = new URL(LOCAL_PROTOCOL, LOCALHOST_VALUE, 0, interfaceClass.getName()).addParameters(map);
invoker = REF_PROTOCOL.refer(interfaceClass, url);
if (logger.isInfoEnabled()) {
logger.info("Using injvm service " + interfaceClass.getName());
}
} else {
urls.clear(); // reference retry init will add url to urls, lead to OOM
if (url != null && url.length() > 0) { // user specified URL, could be peer-to-peer address, or register center's address.
String[] us = SEMICOLON_SPLIT_PATTERN.split(url);
if (us != null && us.length > 0) {
for (String u : us) {
URL url = URL.valueOf(u);
if (StringUtils.isEmpty(url.getPath())) {
url = url.setPath(interfaceName);
}
if (REGISTRY_PROTOCOL.equals(url.getProtocol())) {
urls.add(url.addParameterAndEncoded(REFER_KEY, StringUtils.toQueryString(map)));
} else {
urls.add(ClusterUtils.mergeUrl(url, map));
}
}
}
} else { // assemble URL from register center's configuration
// if protocols not injvm checkRegistry
if (!LOCAL_PROTOCOL.equalsIgnoreCase(getProtocol())){
checkRegistry();
List<URL> us = loadRegistries(false);
if (CollectionUtils.isNotEmpty(us)) {
for (URL u : us) {
URL monitorUrl = loadMonitor(u);
if (monitorUrl != null) {
map.put(MONITOR_KEY, URL.encode(monitorUrl.toFullString()));
}
urls.add(u.addParameterAndEncoded(REFER_KEY, StringUtils.toQueryString(map)));
}
}
if (urls.isEmpty()) {
throw new IllegalStateException("No such any registry to reference " + interfaceName + " on the consumer " + NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion() + ", please config <dubbo:registry address=\"...\" /> to your spring config.");
}
}
}
//笔者注: REF_PROTOCOL是一个SPI扩展，对于使用zookeeper注册中心来说实际会调用RegistryProtocol.refer.
//RegistryProtocol会创建消费者节点，消费者节点的path带上了当前时间戳
if (urls.size() == 1) {
invoker = REF_PROTOCOL.refer(interfaceClass, urls.get(0));
} else {
List<Invoker<?>> invokers = new ArrayList<Invoker<?>>();
URL registryURL = null;
for (URL url : urls) {
invokers.add(REF_PROTOCOL.refer(interfaceClass, url));
if (REGISTRY_PROTOCOL.equals(url.getProtocol())) {
registryURL = url; // use last registry url
}
}
if (registryURL != null) { // registry url is available
// use RegistryAwareCluster only when register's CLUSTER is available
URL u = registryURL.addParameter(CLUSTER_KEY, RegistryAwareCluster.NAME);
// The invoker wrap relation would be: RegistryAwareClusterInvoker(StaticDirectory) -> FailoverClusterInvoker(RegistryDirectory, will execute route) -> Invoker
invoker = CLUSTER.join(new StaticDirectory(u, invokers));
} else { // not a registry url, must be direct invoke.
invoker = CLUSTER.join(new StaticDirectory(invokers));
}
}
}
//笔者注：如果需要check服务提供者 则校验服务是否可用。如果服务不可用，则直接抛异常，
//并没有给ref设置值，但是前面已经在zk上创建了消费者节点
if (shouldCheck() && !invoker.isAvailable()) {
throw new IllegalStateException("Failed to check the status of the service " + interfaceName + ". No provider available for the service " + (group == null ? "" : group + "/") + interfaceName + (version == null ? "" : ":" + version) + " from the url " + invoker.getUrl() + " to the consumer " + NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion());
}
if (logger.isInfoEnabled()) {
logger.info("Refer dubbo service " + interfaceClass.getName() + " from url " + invoker.getUrl());
}
/**
* @since 2.7.0
* ServiceData Store
*/
MetadataReportService metadataReportService = null;
if ((metadataReportService = getMetadataReportService()) != null) {
URL consumerURL = new URL(CONSUMER_PROTOCOL, map.remove(REGISTER_IP_KEY), 0, map.get(INTERFACE_KEY), map);
metadataReportService.publishConsumer(consumerURL);
}
// create service proxy
return (T) PROXY_FACTORY.getProxy(invoker);
}
...
}
下面是6次泛型调用服务"com.test.dubbogeneric.TestService"(没有提供者)之后的zk节点，创建了6个消费者，这些个消费者path除了timestamp不一样外其余都一模一样。
使用url解码之后更清晰
[
consumer://172.28.253.130/org.apache.dubbo.rpc.service.GenericService?application=test&category=consumers&check=false&dubbo=2.0.2&generic=true&interface=com.test.dubbogeneric.TestService&lazy=false&pid=7905&release=2.7.3&retries=0&side=consumer&sticky=false&timeout=3000×tamp=1592036013311,
consumer://172.28.253.130/org.apache.dubbo.rpc.service.GenericService?application=test&category=consumers&check=false&dubbo=2.0.2&generic=true&interface=com.test.dubbogeneric.TestService&lazy=false&pid=7905&release=2.7.3&retries=0&side=consumer&sticky=false&timeout=3000×tamp=1592036035633,
consumer://172.28.253.130/org.apache.dubbo.rpc.service.GenericService?application=test&category=consumers&check=false&dubbo=2.0.2&generic=true&interface=com.test.dubbogeneric.TestService&lazy=false&pid=7905&release=2.7.3&retries=0&side=consumer&sticky=false&timeout=3000×tamp=1592036036773,
consumer://172.28.253.130/org.apache.dubbo.rpc.service.GenericService?application=test&category=consumers&check=false&dubbo=2.0.2&generic=true&interface=com.test.dubbogeneric.TestService&lazy=false&pid=7905&release=2.7.3&retries=0&side=consumer&sticky=false&timeout=3000×tamp=1592036037948,
consumer://172.28.253.130/org.apache.dubbo.rpc.service.GenericService?application=test&category=consumers&check=false&dubbo=2.0.2&generic=true&interface=com.test.dubbogeneric.TestService&lazy=false&pid=7905&release=2.7.3&retries=0&side=consumer&sticky=false&timeout=3000×tamp=1592036039105,
consumer://172.28.253.130/org.apache.dubbo.rpc.service.GenericService?application=test&category=consumers&check=false&dubbo=2.0.2&generic=true&interface=com.test.dubbogeneric.TestService&lazy=false&pid=7905&release=2.7.3&retries=0&side=consumer&sticky=false&timeout=3000×tamp=1592036040226]
如何解决
解决方案有3个
- 1.【推荐】升级dubbo版本到2.7.7(包括)以上，2.7.7版本判断服务不可用时，执行了destroy操作会删除之前创建消费者节点
if (shouldCheck() && !invoker.isAvailable()) { //笔者注： 2.7.7版本增加的destroy操作 invoker.destroy(); throw new IllegalStateException("Failed to check the status of the service " + interfaceName + ". No provider available for the service " + (group == null ? "" : group + "/") + interfaceName + (version == null ? "" : ":" + version) + " from the url " + invoker.getUrl() + " to the consumer " + NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion()); } - 2.【推荐】泛型调用创建ReferenceConfig时设置check=false，即
reference.setCheck(false);设置false以后，init过程就不会校验服务是否可用，也就不抛异常，ref就不会为空。第2次、第3次、第n次获取"服务引用"时都直接返回第1次的ref，也就不会创建zk节点
- 3. 捕获异常，通过java的泛型获取invoker，然后调用invoker的destroy来删除zk节点