現象
使用dubbo的開發者對dubbo泛化調用肯定不陌生。我們在定時任務管理場景中使用dubbo的泛化調用（泛化調用dubbo接口）。一次，同事在測試環境配置定時任務 10s執行一次，但是配置的接口並沒有提供者。過不多久，zookeeper上就有了上萬個消費者節點。
官方dubbo泛化調用的示例是這樣的：
ReferenceConfig獲取"服務引用"的時候先取已經實例化的"服務引用"，如果沒有實例化過則會調用init來實例化"服務引用"。實例化"服務引用"過程默認要check提供者是否存在，不存在則拋異常導致實例化失敗(此時已經在zookeeper上創建了消費者節點)。下一次通過ReferenceConfig獲取"服務引用"又會失敗(也會創建消費者節點，消費者節點上會帶上時間戳所以每次都會創建新的節點)。如此反覆，就會無窮盡的創建zk節點。 看一下ReferenceConfig獲取"服務引用"的源碼（關鍵位置筆者加了注視）：
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!");
}
// 筆者注： 是否已經實例化了"服務引用"， 沒有則調用init實例化"服務引用"
if (ref == null) {
init();
}
return ref;
}
//筆者注：初始化"服務引用"
private void init() {
if (initialized) {
return;
}
checkStubAndLocal(interfaceClass);
checkMock(interfaceClass);
Map<String, String> map = new HashMap<String, String>();
map.put(SIDE_KEY, CONSUMER_SIDE);
//筆者注：這裏拼接上了"時間戳"的參數
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);
// 筆者注: createProxy拋異常的化 ref就沒有設置值，仍然爲空
ref = createProxy(map);
String serviceKey = URL.buildKey(interfaceName, group, version);
ApplicationModel.initConsumerModel(serviceKey, buildConsumerModel(serviceKey, attributes));
initialized = true;
}
//筆者注： 創建"服務引用" 實例，
//(1)先在zk上創建一個消費者節點
//(2)校驗服務是否可用(如果配置了需要校驗)，不可用拋異常
//(3)創建一個代理對象
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.");
}
}
}
//筆者注: REF_PROTOCOL是一個SPI擴展，對於使用zookeeper註冊中心來說實際會調用RegistryProtocol.refer.
//RegistryProtocol會創建消費者節點，消費者節點的path帶上了當前時間戳
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));
}
}
}
//筆者注：如果需要check服務提供者 則校驗服務是否可用。如果服務不可用，則直接拋異常，
//並沒有給ref設置值，但是前面已經在zk上創建了消費者節點
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次泛型調用服務"com.test.dubbogeneric.TestService"(沒有提供者)之後的zk節點，創建了6個消費者，這些個消費者path除了timestamp不一樣外其餘都一模一樣。
使用url解碼之後更清晰
[
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]
如何解決
解決方案有3個
- 1.【推薦】升級dubbo版本到2.7.7(包括)以上，2.7.7版本判斷服務不可用時，執行了destroy操作會刪除之前創建消費者節點
if (shouldCheck() && !invoker.isAvailable()) { //筆者注： 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.【推薦】泛型調用創建ReferenceConfig時設置check=false，即
reference.setCheck(false);設置false以後，init過程就不會校驗服務是否可用，也就不拋異常，ref就不會爲空。第2次、第3次、第n次獲取"服務引用"時都直接返回第1次的ref，也就不會創建zk節點
- 3. 捕獲異常，通過java的泛型獲取invoker，然後調用invoker的destroy來刪除zk節點