dubbo消費者啟動報錯分析
- 2020 年 3 月 10 日
- 筆記
環境
os: MacBook Produbbo: 2.7.5java: 1.8
問題
運行dubbo-demo-xml-consumer項目，控制台報以下錯誤:
java.lang.IllegalStateException: There's no ApplicationConfig specified. at org.apache.dubbo.config.context.ConfigManager.lambda$getApplicationOrElseThrow$0(ConfigManager.java:88) at java.util.Optional.orElseThrow(Optional.java:290) at org.apache.dubbo.config.context.ConfigManager.getApplicationOrElseThrow(ConfigManager.java:88) at org.apache.dubbo.rpc.model.ApplicationModel.getApplicationConfig(ApplicationModel.java:100) at org.apache.dubbo.registry.integration.RegistryProtocol.destroy(RegistryProtocol.java:500) at org.apache.dubbo.rpc.protocol.ProtocolFilterWrapper.destroy(ProtocolFilterWrapper.java:166) at org.apache.dubbo.rpc.protocol.ProtocolListenerWrapper.destroy(ProtocolListenerWrapper.java:80) at org.apache.dubbo.config.DubboShutdownHook.destroyProtocols(DubboShutdownHook.java:140) at org.apache.dubbo.config.DubboShutdownHook.destroyAll(DubboShutdownHook.java:124) at org.apache.dubbo.config.bootstrap.DubboBootstrap.destroy(DubboBootstrap.java:1037) at org.apache.dubbo.config.bootstrap.DubboBootstrap.stop(DubboBootstrap.java:817) at org.apache.dubbo.config.spring.context.DubboBootstrapApplicationListener.onContextClosedEvent(DubboBootstrapApplicationListener.java:65) at org.apache.dubbo.config.spring.context.DubboBootstrapApplicationListener.onApplicationContextEvent(DubboBootstrapApplicationListener.java:55) at org.apache.dubbo.config.spring.context.OneTimeExecutionApplicationContextEventListener.onApplicationEvent(OneTimeExecutionApplicationContextEventListener.java:40) at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172) at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165) at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139) at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:393) at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:347) at org.springframework.context.support.AbstractApplicationContext.doClose(AbstractApplicationContext.java:991) at org.springframework.context.support.AbstractApplicationContext$2.run(AbstractApplicationContext.java:929)
根據列印出來的日誌，方法調用棧為
通過圖可知 org.apache.dubbo.registry.integration.RegistryProtocol#destroy該方法都會在 org.apache.dubbo.config.bootstrap.DubboBootstrap#destroy中被調用，而且是通過Spring ContextClosedEvent事件(容器關閉時)、JVM鉤子函數(JVM退出)觸發。報錯的具體位置，在方法 org.apache.dubbo.config.context.ConfigManager#getApplicationOrElseThrow中，通過斷點分析 org.apache.dubbo.config.context.ConfigManager#getConfig(java.lang.String)中獲取配置資訊時， configsCache為空，所以該方法的返回值為null，上層方法就報錯了。
protected <C extends AbstractConfig> C getConfig(String configType) throws IllegalStateException { return read(() -> { Map<String, C> configsMap = (Map) configsCache.getOrDefault(configType, emptyMap()); int size = configsMap.size(); if (size < 1) {// throw new IllegalStateException("No such " + configType.getName() + " is found"); return null; } else if (size > 1) { logger.warn("Expected single matching of " + configType + ", but found " + size + " instances, will randomly pick the first one."); } return configsMap.values().iterator().next(); }); }
已經定位到報錯的位置，奇怪的是，運行dubbo-demo-api-consumer項目時，卻不報錯，那具體原因是什麼呢？
分析
configsCache什麼時候會被刪除呢，通過程式碼可發現，在 org.apache.dubbo.config.context.ConfigManager#clear方法中會刪除：
public void clear() { write(() -> { this.configsCache.clear(); }); }
而該方法只會在 org.apache.dubbo.config.bootstrap.DubboBootstrap#clearConfigs中被調用(除單元測試外)，該方法的調用棧:
通過調用棧發現 org.apache.dubbo.config.context.ConfigManager#clear也會在 org.apache.dubbo.config.bootstrap.DubboBootstrap#destroy被調用，而 destroy同樣會被Spring ContextClosedEvent事件(容器關閉時)、JVM鉤子函數(JVM退出)觸發。到這裡，猜想: 在dubbo-demo-xml-consumer中運行程式結束後，Spring容器關閉時，會觸發ContextClosedEvent事件[A]，而JVM退出時也會觸發鉤子函數[B]，兩個都會去銷毀快取的配置資訊等，存在[A]銷毀了配置資訊，即上文中 configsCache，而[B]此時從快取中沒有獲取到配置就會報錯，實際通過斷點調試確實如此。
總結
雖然這個錯誤不會導致程式的結果，但是報錯的確讓人很疑惑，如果不深入分析很難找到問題所在。
