title: 为什么说dubbo的声明式缓存不好用！！！ tags:

• dubbo
• mock
• zookeeper
• cache
• cluster categories: dubbo date: 2017-06-25 18:18:53

前几篇我们分析了dubbo的缓存以及缓存依赖的机制（filter）

• dubbo源码系列之filter的今世 (f6car)
• dubbo源码系列之filter的前生 (f6car
• dubbo缓存代码分析 (f6car）

那么通常提供缓存的目的是什么呢？

关于两级缓存的说明

通常为了更快的速度（以及一定的稳定性）

那么dubbo中的实现是通过filter机制基本上来缓存了我们需要结果。

但是默认提供的缓存并没有清空机制（不能提供供用户直接刷新缓存的机制）

我们系统中较为简单的是提供jmx来共用户刷新mac环境下ehcache 广播rmi异常解决&JMX相关

其次缓存提供了更好的稳定性，通常第三方服务挂了时候对于已经缓存好的数据可以直接获取缓存数据。

那么dubbo中的实现如何呢？下面来分析一下

对于稳定性来说我们一本是站在客户端的角度的。那么我们先从ReferneceBean开始分析

抛开spring对于RefenenceBean的初始化过程，直接进入RefenenceBean的init方法。

    private void init() {if (initialized) {return;}initialized = true;if (interfaceName == null || interfaceName.length() == 0) {throw new IllegalStateException("<dubbo:reference interface=\"\" /> interface not allow null!");}// 获取消费者全局配置checkDefault();appendProperties(this);if (getGeneric() == null && getConsumer() != null) {setGeneric(getConsumer().getGeneric());}if (ProtocolUtils.isGeneric(getGeneric())) {interfaceClass = GenericService.class;} else {try {interfaceClass = Class.forName(interfaceName, true, Thread.currentThread().getContextClassLoader());} catch (ClassNotFoundException e) {throw new IllegalStateException(e.getMessage(), e);}checkInterfaceAndMethods(interfaceClass, methods);}String resolve = System.getProperty(interfaceName);String resolveFile = null;if (resolve == null || resolve.length() == 0) {resolveFile = System.getProperty("dubbo.resolve.file");if (resolveFile == null || resolveFile.length() == 0) {File userResolveFile = new File(new File(System.getProperty("user.home")), "dubbo-resolve.properties");if (userResolveFile.exists()) {resolveFile = userResolveFile.getAbsolutePath();}}if (resolveFile != null && resolveFile.length() > 0) {Properties properties = new Properties();FileInputStream fis = null;try {fis = new FileInputStream(new File(resolveFile));properties.load(fis);} catch (IOException e) {throw new IllegalStateException("Unload " + resolveFile + ", cause: " + e.getMessage(), e);} finally {try {if(null != fis) fis.close();} catch (IOException e) {logger.warn(e.getMessage(), e);}}resolve = properties.getProperty(interfaceName);}}if (resolve != null && resolve.length() > 0) {url = resolve;if (logger.isWarnEnabled()) {if (resolveFile != null && resolveFile.length() > 0) {logger.warn("Using default dubbo resolve file " + resolveFile + " replace " + interfaceName + "" + resolve + " to p2p invoke remote service.");} else {logger.warn("Using -D" + interfaceName + "=" + resolve + " to p2p invoke remote service.");}}}if (consumer != null) {if (application == null) {application = consumer.getApplication();}if (module == null) {module = consumer.getModule();}if (registries == null) {registries = consumer.getRegistries();}if (monitor == null) {monitor = consumer.getMonitor();}}if (module != null) {if (registries == null) {registries = module.getRegistries();}if (monitor == null) {monitor = module.getMonitor();}}if (application != null) {if (registries == null) {registries = application.getRegistries();}if (monitor == null) {monitor = application.getMonitor();}}checkApplication();checkStubAndMock(interfaceClass);Map<String, String> map = new HashMap<String, String>();Map<Object, Object> attributes = new HashMap<Object, Object>();map.put(Constants.SIDE_KEY, Constants.CONSUMER_SIDE);map.put(Constants.DUBBO_VERSION_KEY, Version.getVersion());map.put(Constants.TIMESTAMP_KEY, String.valueOf(System.currentTimeMillis()));if (ConfigUtils.getPid() > 0) {map.put(Constants.PID_KEY, String.valueOf(ConfigUtils.getPid()));}if (! isGeneric()) {String revision = Version.getVersion(interfaceClass, version);if (revision != null && revision.length() > 0) {map.put("revision", revision);}String[] methods = Wrapper.getWrapper(interfaceClass).getMethodNames();if(methods.length == 0) {logger.warn("NO method found in service interface " + interfaceClass.getName());map.put("methods", Constants.ANY_VALUE);}else {map.put("methods", StringUtils.join(new HashSet<String>(Arrays.asList(methods)), ","));}}map.put(Constants.INTERFACE_KEY, interfaceName);appendParameters(map, application);appendParameters(map, module);appendParameters(map, consumer, Constants.DEFAULT_KEY);appendParameters(map, this);String prifix = StringUtils.getServiceKey(map);if (methods != null && methods.size() > 0) {for (MethodConfig method : methods) {appendParameters(map, method, method.getName());String retryKey = method.getName() + ".retry";if (map.containsKey(retryKey)) {String retryValue = map.remove(retryKey);if ("false".equals(retryValue)) {map.put(method.getName() + ".retries", "0");}}appendAttributes(attributes, method, prifix + "." + method.getName());checkAndConvertImplicitConfig(method, map, attributes);}}//attributes通过系统context进行存储.StaticContext.getSystemContext().putAll(attributes);ref = createProxy(map);}
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除开一些必要的设置之外，主要进入createProxy方法

    @SuppressWarnings({ "unchecked", "rawtypes", "deprecation" })private T createProxy(Map<String, String> map) {URL tmpUrl = new URL("temp", "localhost", 0, map);final boolean isJvmRefer;if (isInjvm() == null) {if (url != null && url.length() > 0) { //指定URL的情况下，不做本地引用isJvmRefer = false;} else if (InjvmProtocol.getInjvmProtocol().isInjvmRefer(tmpUrl)) {//默认情况下如果本地有服务暴露，则引用本地服务.isJvmRefer = true;} else {isJvmRefer = false;}} else {isJvmRefer = isInjvm().booleanValue();}if (isJvmRefer) {URL url = new URL(Constants.LOCAL_PROTOCOL, NetUtils.LOCALHOST, 0, interfaceClass.getName()).addParameters(map);invoker = refprotocol.refer(interfaceClass, url);if (logger.isInfoEnabled()) {logger.info("Using injvm service " + interfaceClass.getName());}} else {if (url != null && url.length() > 0) { // 用户指定URL，指定的URL可能是对点对直连地址，也可能是注册中心URLString[] us = Constants.SEMICOLON_SPLIT_PATTERN.split(url);if (us != null && us.length > 0) {for (String u : us) {URL url = URL.valueOf(u);if (url.getPath() == null || url.getPath().length() == 0) {url = url.setPath(interfaceName);}if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {urls.add(url.addParameterAndEncoded(Constants.REFER_KEY, StringUtils.toQueryString(map)));} else {urls.add(ClusterUtils.mergeUrl(url, map));}}}} else { // 通过注册中心配置拼装URLList<URL> us = loadRegistries(false);if (us != null && us.size() > 0) {for (URL u : us) {URL monitorUrl = loadMonitor(u);if (monitorUrl != null) {map.put(Constants.MONITOR_KEY, URL.encode(monitorUrl.toFullString()));}urls.add(u.addParameterAndEncoded(Constants.REFER_KEY, StringUtils.toQueryString(map)));}}if (urls == null || urls.size() == 0) {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.");}}if (urls.size() == 1) {invoker = refprotocol.refer(interfaceClass, urls.get(0));} else {List<Invoker<?>> invokers = new ArrayList<Invoker<?>>();URL registryURL = null;for (URL url : urls) {invokers.add(refprotocol.refer(interfaceClass, url));if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {registryURL = url; // 用了最后一个registry url}}if (registryURL != null) { // 有 注册中心协议的URL// 对有注册中心的Cluster 只用 AvailableClusterURL u = registryURL.addParameter(Constants.CLUSTER_KEY, AvailableCluster.NAME);invoker = cluster.join(new StaticDirectory(u, invokers));}  else { // 不是 注册中心的URLinvoker = cluster.join(new StaticDirectory(invokers));}}}Boolean c = check;if (c == null && consumer != null) {c = consumer.isCheck();}if (c == null) {c = true; // default true}if (c && ! 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());}// 创建服务代理return (T) proxyFactory.getProxy(invoker);}
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便于说明我们此处使用zookeeper作为协议 可以看到此处我们走到的业务逻辑为

    List<URL> us = loadRegistries(false);protected List<URL> loadRegistries(boolean provider) {checkRegistry();List<URL> registryList = new ArrayList<URL>();if (registries != null && registries.size() > 0) {for (RegistryConfig config : registries) {String address = config.getAddress();if (address == null || address.length() == 0) {address = Constants.ANYHOST_VALUE;}String sysaddress = System.getProperty("dubbo.registry.address");if (sysaddress != null && sysaddress.length() > 0) {address = sysaddress;}if (address != null && address.length() > 0&& ! RegistryConfig.NO_AVAILABLE.equalsIgnoreCase(address)) {Map<String, String> map = new HashMap<String, String>();appendParameters(map, application);appendParameters(map, config);map.put("path", RegistryService.class.getName());map.put("dubbo", Version.getVersion());map.put(Constants.TIMESTAMP_KEY, String.valueOf(System.currentTimeMillis()));if (ConfigUtils.getPid() > 0) {map.put(Constants.PID_KEY, String.valueOf(ConfigUtils.getPid()));}if (! map.containsKey("protocol")) {if (ExtensionLoader.getExtensionLoader(RegistryFactory.class).hasExtension("remote")) {map.put("protocol", "remote");} else {map.put("protocol", "dubbo");}}List<URL> urls = UrlUtils.parseURLs(address, map);for (URL url : urls) {url = url.addParameter(Constants.REGISTRY_KEY, url.getProtocol());url = url.setProtocol(Constants.REGISTRY_PROTOCOL);if ((provider && url.getParameter(Constants.REGISTER_KEY, true))|| (! provider && url.getParameter(Constants.SUBSCRIBE_KEY, true))) {registryList.add(url);}}}}}return registryList;}通篇最重要的就是设置了Protocol为Constants.REGISTRY\_PROTOCOL 因此我们可以认为此处使用的是RegistryProtocol 。private <T> Invoker<T> doRefer(Cluster cluster, Registry registry, Class<T> type, URL url) {RegistryDirectory<T> directory = new RegistryDirectory<T>(type, url);directory.setRegistry(registry);directory.setProtocol(protocol);URL subscribeUrl = new URL(Constants.CONSUMER_PROTOCOL, NetUtils.getLocalHost(), 0, type.getName(), directory.getUrl().getParameters());if (! Constants.ANY_VALUE.equals(url.getServiceInterface())&& url.getParameter(Constants.REGISTER_KEY, true)) {registry.register(subscribeUrl.addParameters(Constants.CATEGORY_KEY, Constants.CONSUMERS_CATEGORY,Constants.CHECK_KEY, String.valueOf(false)));}directory.subscribe(subscribeUrl.addParameter(Constants.CATEGORY_KEY,Constants.PROVIDERS_CATEGORY+ "," + Constants.CONFIGURATORS_CATEGORY+ "," + Constants.ROUTERS_CATEGORY));return cluster.join(directory);}
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RegistryProtocol在生成Invoker时使用了Cluster，那么这个Cluster是啥呢？

通常来说指的是（使用*或者复杂分组）

    private Cluster getMergeableCluster() {return ExtensionLoader.getExtensionLoader(Cluster.class).getExtension("mergeable");}
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而cluster对于来说spi如下

    mock=com.alibaba.dubbo.rpc.cluster.support.wrapper.MockClusterWrapper    failover=com.alibaba.dubbo.rpc.cluster.support.FailoverCluster    failfast=com.alibaba.dubbo.rpc.cluster.support.FailfastCluster    failsafe=com.alibaba.dubbo.rpc.cluster.support.FailsafeCluster    failback=com.alibaba.dubbo.rpc.cluster.support.FailbackCluster    forking=com.alibaba.dubbo.rpc.cluster.support.ForkingCluster    available=com.alibaba.dubbo.rpc.cluster.support.AvailableCluster    mergeable=com.alibaba.dubbo.rpc.cluster.support.MergeableCluster    broadcast=com.alibaba.dubbo.rpc.cluster.support.BroadcastCluster复制代码

其中MockClusterWrapper是对应的wrapper 参考 dubbo源码系列之filter的前生

    */public class MockClusterWrapper implements Cluster {private Cluster cluster;public MockClusterWrapper(Cluster cluster) {this.cluster = cluster;}public <T> Invoker<T> join(Directory<T> directory) throws RpcException {return new MockClusterInvoker<T>(directory,this.cluster.join(directory));}}
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那么可以确定生成的Invoker就是MockClusterInvoker

这个Mock中注入的为cluster接口spi默认为failover

    @SPI(FailoverCluster.NAME)public interface Cluster {/*** Merge the directory invokers to a virtual invoker.** @param <T>* @param directory* @return cluster invoker* @throws RpcException*/@Adaptive<T> Invoker<T> join(Directory<T> directory) throws RpcException;}
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参考说明

我们获取到了一个FailoverClusterInvoker

注意此处是由FailoverCluster直接new的，换言之没有任何包装和代理

    public class FailoverCluster implements Cluster {public final static String NAME = "failover";public <T> Invoker<T> join(Directory<T> directory) throws RpcException {return new FailoverClusterInvoker<T>(directory);}}
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那么我们在实际调用的时候（上述情景）使用的是由MockClusterInvoker委托的FailoverClusterInvoker

出现MockClusterInvoker的主要原因应该是可以直接使用dubbo的 mock功能可以在服务调用结束时收尾（做其他处理）===》此处先不提stub

那么每次调用均会执行到

 @SuppressWarnings({ "unchecked", "rawtypes" })public Result doInvoke(Invocation invocation, final List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {List<Invoker<T>> copyinvokers = invokers;checkInvokers(copyinvokers, invocation);int len = getUrl().getMethodParameter(invocation.getMethodName(), Constants.RETRIES_KEY, Constants.DEFAULT_RETRIES) + 1;if (len <= 0) {len = 1;}// retry loop.RpcException le = null; // last exception.List<Invoker<T>> invoked = new ArrayList<Invoker<T>>(copyinvokers.size()); // invoked invokers.Set<String> providers = new HashSet<String>(len);for (int i = 0; i < len; i++) {//重试时，进行重新选择，避免重试时invoker列表已发生变化.//注意：如果列表发生了变化，那么invoked判断会失效，因为invoker示例已经改变if (i > 0) {checkWheatherDestoried();copyinvokers = list(invocation);//重新检查一下checkInvokers(copyinvokers, invocation);}Invoker<T> invoker = select(loadbalance, invocation, copyinvokers, invoked);invoked.add(invoker);RpcContext.getContext().setInvokers((List)invoked);try {Result result = invoker.invoke(invocation);if (le != null && logger.isWarnEnabled()) {logger.warn("Although retry the method " + invocation.getMethodName()+ " in the service " + getInterface().getName()+ " was successful by the provider " + invoker.getUrl().getAddress()+ ", but there have been failed providers " + providers+ " (" + providers.size() + "/" + copyinvokers.size()+ ") from the registry " + directory.getUrl().getAddress()+ " on the consumer " + NetUtils.getLocalHost()+ " using the dubbo version " + Version.getVersion() + ". Last error is: "+ le.getMessage(), le);}return result;} catch (RpcException e) {if (e.isBiz()) { // biz exception.throw e;}le = e;} catch (Throwable e) {le = new RpcException(e.getMessage(), e);} finally {providers.add(invoker.getUrl().getAddress());}}throw new RpcException(le != null ? le.getCode() : 0, "Failed to invoke the method "+ invocation.getMethodName() + " in the service " + getInterface().getName()+ ". Tried " + len + " times of the providers " + providers+ " (" + providers.size() + "/" + copyinvokers.size()+ ") from the registry " + directory.getUrl().getAddress()+ " on the consumer " + NetUtils.getLocalHost() + " using the dubbo version "+ Version.getVersion() + ". Last error is: "+ (le != null ? le.getMessage() : ""), le != null && le.getCause() != null ? le.getCause() : le);}protected  List<Invoker<T>> list(Invocation invocation) throws RpcException {List<Invoker<T>> invokers = directory.list(invocation);return invokers;}public List<Invoker<T>> doList(Invocation invocation) {if (forbidden) {throw new RpcException(RpcException.FORBIDDEN_EXCEPTION, "Forbid consumer " +  NetUtils.getLocalHost() + " access service " + getInterface().getName() + " from registry " + getUrl().getAddress() + " use dubbo version " + Version.getVersion() + ", Please check registry access list (whitelist/blacklist).");}List<Invoker<T>> invokers = null;Map<String, List<Invoker<T>>> localMethodInvokerMap = this.methodInvokerMap; // local referenceif (localMethodInvokerMap != null && localMethodInvokerMap.size() > 0) {String methodName = RpcUtils.getMethodName(invocation);Object[] args = RpcUtils.getArguments(invocation);if(args != null && args.length > 0 && args[0] != null&& (args[0] instanceof String || args[0].getClass().isEnum())) {invokers = localMethodInvokerMap.get(methodName + "." + args[0]); // 可根据第一个参数枚举路由}if(invokers == null) {invokers = localMethodInvokerMap.get(methodName);}if(invokers == null) {invokers = localMethodInvokerMap.get(Constants.ANY_VALUE);}if(invokers == null) {Iterator<List<Invoker<T>>> iterator = localMethodInvokerMap.values().iterator();if (iterator.hasNext()) {invokers = iterator.next();}}}return invokers == null ? new ArrayList<Invoker<T>>(0) : invokers;}
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那么即使此刻有缓存的时候我们也无法使用该缓存，因为缓存的CacheFilter根本没有机会执行，反而直接报错。那么使用声明式缓存完成dubbo稳定性的美梦破灭了。

接着分析，上述代码中的字段forbidden是何时被指为true的呢？

    /*** 根据invokerURL列表转换为invoker列表。转换规则如下：* 1.如果url已经被转换为invoker，则不在重新引用，直接从缓存中获取，注意如果url中任何一个参数变更也会重新引用* 2.如果传入的invoker列表不为空，则表示最新的invoker列表* 3.如果传入的invokerUrl列表是空，则表示只是下发的override规则或route规则，需要重新交叉对比，决定是否需要重新引用。* @param invokerUrls 传入的参数不能为null*/private void refreshInvoker(List<URL> invokerUrls){if (invokerUrls != null && invokerUrls.size() == 1 && invokerUrls.get(0) != null&& Constants.EMPTY_PROTOCOL.equals(invokerUrls.get(0).getProtocol())) {this.forbidden = true; // 禁止访问this.methodInvokerMap = null; // 置空列表destroyAllInvokers(); // 关闭所有Invoker} else {this.forbidden = false; // 允许访问Map<String, Invoker<T>> oldUrlInvokerMap = this.urlInvokerMap; // local referenceif (invokerUrls.size() == 0 && this.cachedInvokerUrls != null){invokerUrls.addAll(this.cachedInvokerUrls);} else {this.cachedInvokerUrls = new HashSet<URL>();this.cachedInvokerUrls.addAll(invokerUrls);//缓存invokerUrls列表，便于交叉对比}if (invokerUrls.size() ==0 ){return;}Map<String, Invoker<T>> newUrlInvokerMap = toInvokers(invokerUrls) ;// 将URL列表转成Invoker列表Map<String, List<Invoker<T>>> newMethodInvokerMap = toMethodInvokers(newUrlInvokerMap); // 换方法名映射Invoker列表// state change//如果计算错误，则不进行处理.if (newUrlInvokerMap == null || newUrlInvokerMap.size() == 0 ){logger.error(new IllegalStateException("urls to invokers error .invokerUrls.size :"+invokerUrls.size() + ", invoker.size :0. urls :"+invokerUrls.toString()));return ;}this.methodInvokerMap = multiGroup ? toMergeMethodInvokerMap(newMethodInvokerMap) : newMethodInvokerMap;this.urlInvokerMap = newUrlInvokerMap;try{destroyUnusedInvokers(oldUrlInvokerMap,newUrlInvokerMap); // 关闭未使用的Invoker}catch (Exception e) {logger.warn("destroyUnusedInvokers error. ", e);}}}```此段代码当invokerUrls中有且仅有一个empty的protocol的URL时将会强行置为true。
```javapublic synchronized void notify(List<URL> urls) {List<URL> invokerUrls = new ArrayList<URL>();List<URL> routerUrls = new ArrayList<URL>();List<URL> configuratorUrls = new ArrayList<URL>();for (URL url : urls) {String protocol = url.getProtocol();String category = url.getParameter(Constants.CATEGORY_KEY, Constants.DEFAULT_CATEGORY);if (Constants.ROUTERS_CATEGORY.equals(category)|| Constants.ROUTE_PROTOCOL.equals(protocol)) {routerUrls.add(url);} else if (Constants.CONFIGURATORS_CATEGORY.equals(category)|| Constants.OVERRIDE_PROTOCOL.equals(protocol)) {configuratorUrls.add(url);} else if (Constants.PROVIDERS_CATEGORY.equals(category)) {invokerUrls.add(url);} else {logger.warn("Unsupported category " + category + " in notified url: " + url + " from registry " + getUrl().getAddress() + " to consumer " + NetUtils.getLocalHost());}}// configuratorsif (configuratorUrls != null && configuratorUrls.size() >0 ){this.configurators = toConfigurators(configuratorUrls);}// routersif (routerUrls != null && routerUrls.size() >0 ){List<Router> routers = toRouters(routerUrls);if(routers != null){ // null - do nothingsetRouters(routers);}}List<Configurator> localConfigurators = this.configurators; // local reference// 合并override参数this.overrideDirectoryUrl = directoryUrl;if (localConfigurators != null && localConfigurators.size() > 0) {for (Configurator configurator : localConfigurators) {this.overrideDirectoryUrl = configurator.configure(overrideDirectoryUrl);}}// providersrefreshInvoker(invokerUrls);}```通常来说我们使用zookeeper作为注册。通常provider在注册一个临时节点（当服务被摘掉时将会自动消失）那么客户端会对对应path进行监听，如果出现childremove
```javaif (zkListener == null) {listeners.putIfAbsent(listener, new ChildListener() {public void childChanged(String parentPath, List<String> currentChilds) {ZookeeperRegistry.this.notify(url, listener, toUrlsWithEmpty(url, parentPath, currentChilds));}});zkListener = listeners.get(listener);}
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此时会对currentChilds进行处理

    private List<URL> toUrlsWithEmpty(URL consumer, String path, List<String> providers) {List<URL> urls = toUrlsWithoutEmpty(consumer, providers);if (urls == null || urls.isEmpty()) {int i = path.lastIndexOf('/');String category = i < 0 ? path : path.substring(i + 1);URL empty = consumer.setProtocol(Constants.EMPTY_PROTOCOL).addParameter(Constants.CATEGORY_KEY, category);urls.add(empty);}return urls;}
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一旦发现当前孩子节点为空那么新建一条protocol为empty的URL放入，此时由于上述代码将会将forbidden置为true，因此出现消费者不能正常获取缓存。

当然对于结果的缓存还是有用处的，但是一般如果单机服务节点出现故障即使存有缓存也无法消费略有些遗憾。

下一篇可以介绍使用Stub或者mock来进行dubbo缓存前置