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  • dubbo的异常栈问题

    1.现象:

        当dubbo provider 抛出异常时,dubbo consumer 在输出异常栈信息时,展示的都是provider 侧的线程栈,这是因为,异常的stackTrace实在在new Throwable()的时候生成的。

          /**
         * Constructs a new throwable with {@code null} as its detail message.
         * The cause is not initialized, and may subsequently be initialized by a
         * call to {@link #initCause}.
         *
         * <p>The {@link #fillInStackTrace()} method is called to initialize
         * the stack trace data in the newly created throwable.
         */
        public Throwable() {
            fillInStackTrace();
        }
    
        /**
         * Fills in the execution stack trace. This method records within this
         * {@code Throwable} object information about the current state of
         * the stack frames for the current thread.
         *
         * <p>If the stack trace of this {@code Throwable} {@linkplain
         * Throwable#Throwable(String, Throwable, boolean, boolean) is not
         * writable}, calling this method has no effect.
         *
         * @return  a reference to this {@code Throwable} instance.
         * @see     java.lang.Throwable#printStackTrace()
         */
        public synchronized Throwable fillInStackTrace() {
            if (stackTrace != null ||
                backtrace != null /* Out of protocol state */ ) {
                fillInStackTrace(0);
                stackTrace = UNASSIGNED_STACK;
            }
            return this;
        }
        //执行native方法
        private native Throwable fillInStackTrace(int dummy);
    



        这里的关键在fillInStackTrace native 方法,会将当前线程栈的信息填充进stackTrace中;但是分布式服务的调用链中各个服务,都是不同进程,更是不同线程,所以这里的stackTrace只会有发生异常的provider的线程栈信息。当consumer接收到异常时,哪怕log出来,也只有provider侧的相关信息,丢失了consumer侧的线程栈信息;而这一现象,在复杂的dubbo调用链中,是无法满足开发人员对异常分析的需求的;


    2.解决办法:

        为了解决这个问题,首先想到的是ExceptionFilter.class,dubbo自带的ExceptionFilter.class是只对provider生效的,对异常是否需要包装成RuntimeException进行判断;那我们可以相应的实现一个consumer侧的ConsumerExceptionFilter去实现,当有provider返回异常时,对异常栈进行追加当前consumer侧的线程栈;这样就变相的实现了跨线程的异常栈了;




        这里是实现代码,为了避免异常栈过大,在代码实现时,追加的异常栈只取了当前服务的执行api行为的位置;(Filter要起作用,是要在org.apache.dubbo.rpc.Filter中添加自定义filter的配置)

    @Activate(group = "consumer")
    public class ConsumerExceptionFilter extends ListenableFilter {
    
        public ConsumerExceptionFilter() {
            super.listener = new ConsumerExceptionFilter.ExceptionListener();
        }
    
    
        @Override
        public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
            return invoker.invoke(invocation);
        }
    
    
        static class ExceptionListener implements Listener {
    
            private Logger logger = LoggerFactory.getLogger(ConsumerExceptionFilter.ExceptionListener.class);
    
            @Override
            public void onResponse(Result appResponse, Invoker<?> invoker, Invocation invocation) {
                if (appResponse.hasException() && GenericService.class != invoker.getInterface()) {
                    try {
                        Throwable exception = appResponse.getException();
    
                        // directly throw if it's checked exception
                        if (!(exception instanceof RuntimeException) && (exception instanceof Exception)) {
                            return;
                        }
    
                        //这段代码的主要目的是为了将consumer方的部分stackTrace追加到provider抛出来的异常的stackTrace
                        //方便在复杂调用环境中,追踪异常位置
                        StackTraceElement[] stackTrace = exception.getStackTrace();
                        StackTraceElement[] newStackTrace = Arrays.copyOf(stackTrace, stackTrace.length + 1);
                        StackTraceElement[] consumerStackTrace = new RuntimeException().getStackTrace();
                        boolean meetProxyElement = false;
                        for (StackTraceElement consumerStackTraceElement : consumerStackTrace) {
    
                            if (meetProxyElement){
                                //这里为了节省资源,只追加一行stackTrace(执行api代码位置的stackTrace)
                                newStackTrace[newStackTrace.length-1] = consumerStackTraceElement;
                                break;
                            }
                            //dubbo的调用使用动态代理,所以stackTraceElement的className会是com.sun.proxy.$Proxy,
                            //它的下一个stackTraceElement就是真正的调用方位置
                            if(
                                Objects.equals(consumerStackTraceElement.getMethodName(), invocation.getMethodName())
                                    && consumerStackTraceElement.getClassName().startsWith("com.sun.proxy")){
                                meetProxyElement = true;
                            }
    
                        }
                        exception.setStackTrace(newStackTrace);
    
                        return;
                    } catch (Throwable e) {
                        logger.warn("Fail to ConsumerExceptionFilter when execute " + RpcContext.getContext().getRemoteHost() + ". service: " + invoker.getInterface().getName() + ", method: " + invocation.getMethodName() + ", exception: " + e.getClass().getName() + ": " + e.getMessage(), e);
                        return;
                    }
                }
            }
    
            @Override
            public void onError(Throwable e, Invoker<?> invoker, Invocation invocation) {
                logger.error("Got unchecked and undeclared exception which from " + RpcContext.getContext().getRemoteHost() + ". service: " + invoker.getInterface().getName() + ", method: " + invocation.getMethodName() + ", exception: " + e.getClass().getName() + ": " + e.getMessage(), e);
    
            }
        }
    }
    
    
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  • 原文地址:https://www.cnblogs.com/IC1101/p/13498041.html
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