深入Dubbo源码 - Dubbo消费者调用过程

// 该类实现InvocationHandler接口，在调用动态代理类方法时会调用invoke方法
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        String methodName = method.getName();
        Class<?>[] parameterTypes = method.getParameterTypes();
        if (method.getDeclaringClass() == Object.class) {
            return method.invoke(invoker, args);
        }
        if ("toString".equals(methodName) && parameterTypes.length == 0) {
            return invoker.toString();
        }
        if ("hashCode".equals(methodName) && parameterTypes.length == 0) {
            return invoker.hashCode();
        }
        if ("equals".equals(methodName) && parameterTypes.length == 1) {
            return invoker.equals(args[0]);
        }
        // 如果是调用基础方法，直接调用invoker的方法并返回。调用其他方法，则将本次调用信息封装成RpcInvocation对象
        // （详见下文）
        return invoker.invoke(new RpcInvocation(method, args)).recreate();
    }

@Override
    public Result invoke(Invocation invocation) throws RpcException {
        Result result = null;

        // 从directory中获取调用的方法信息中存储的配置信息Constants.MOCK_KEY（是否使用mock模式，默认为false）
        String value = directory.getUrl().getMethodParameter(invocation.getMethodName(), Constants.MOCK_KEY, Boolean.FALSE.toString()).trim();
        // 如果为false，则调用真实服务提供者
        if (value.length() == 0 || value.equalsIgnoreCase("false")) {
            //no mock
            result = this.invoker.invoke(invocation);
        } else if (value.startsWith("force")) {// 如果该配置以force开头，则进行强制mock调用，执行doMockInvoke方法（具体可查看方法内实现，该内容不是本文重点）
            if (logger.isWarnEnabled()) {
                logger.info("force-mock: " + invocation.getMethodName() + " force-mock enabled , url : " + directory.getUrl());
            }
            //force:direct mock
            result = doMockInvoke(invocation, null);
        } else {// 其他配置，则优先调用服务提供者，如果失败再进行mock
            //fail-mock
            try {
                // （详见下文）
                result = this.invoker.invoke(invocation);
            } catch (RpcException e) {
                if (e.isBiz()) {
                    throw e;
                } else {
                    if (logger.isWarnEnabled()) {
                        logger.warn("fail-mock: " + invocation.getMethodName() + " fail-mock enabled , url : " + directory.getUrl(), e);
                    }
                    // 会catch RpcException异常，失败后执行doMockInvoke方法
                    result = doMockInvoke(invocation, e);
                }
            }
        }
        return result;
    }

@Override
    public Result invoke(final Invocation invocation) throws RpcException {
        checkWhetherDestroyed();
        LoadBalance loadbalance = null;

        // 查看线程变量InternalThreadLocal中获取上下文对象RpcContext，查看RpcContext中是否有"附件"属性，如果有，则本次调用invocation加入该属性
        // binding attachments into invocation.
        Map<String, String> contextAttachments = RpcContext.getContext().getAttachments();
        if (contextAttachments != null && contextAttachments.size() != 0) {
            ((RpcInvocation) invocation).addAttachments(contextAttachments);
        }

        // 从directory中获取invokers list（查看directory对象，该list可通过notify方法与注册中心交互更新）
        List<Invoker<T>> invokers = list(invocation);
        if (invokers != null && !invokers.isEmpty()) {
            // 获取负载均衡策略，未配置则默认随机策略RandomLoadBalance
            loadbalance = ExtensionLoader.getExtensionLoader(LoadBalance.class).getExtension(invokers.get(0).getUrl()
                    .getMethodParameter(RpcUtils.getMethodName(invocation), Constants.LOADBALANCE_KEY, Constants.DEFAULT_LOADBALANCE));
        }
        RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
        // 执行子类doInvoke方法（详见下文）
        return doInvoke(invocation, invokers, loadbalance);
    }

public Result doInvoke(Invocation invocation, final List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
        List<Invoker<T>> copyinvokers = invokers;
        // 检查invokers，为空则抛出异常RpcException
        checkInvokers(copyinvokers, invocation);
        // 获取重试次数，默认是2次
        int len = getUrl().getMethodParameter(invocation.getMethodName(), Constants.RETRIES_KEY, Constants.DEFAULT_RETRIES) + 1;
        // 如果配置不当，则将次数置为1
        if (len <= 0) {
            len = 1;
        }
        // retry loop.   循环调用
        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++) {
            //Reselect before retry to avoid a change of candidate `invokers`.
            //NOTE: if `invokers` changed, then `invoked` also lose accuracy.
            if (i > 0) {
                checkWhetherDestroyed();
                copyinvokers = list(invocation);
                // check again   再一次检查，防止在调用过程中list中的invoker变化
                checkInvokers(copyinvokers, invocation);
            }
            // 通过不同的负载均衡策略选择一个invoker
            Invoker<T> invoker = select(loadbalance, invocation, copyinvokers, invoked);
            // 将已经选择出的invoker存放在另一个list中
            invoked.add(invoker);
            RpcContext.getContext().setInvokers((List) invoked);
            try {
                // 发起调用（详见下文）
                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);
    }

@Override
    public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
        // 用RpcContext存储调用的上下文信息
        RpcContext.getContext()
                .setInvoker(invoker)
                .setInvocation(invocation)
                .setLocalAddress(NetUtils.getLocalHost(), 0)
                .setRemoteAddress(invoker.getUrl().getHost(),
                        invoker.getUrl().getPort());
        if (invocation instanceof RpcInvocation) {
            ((RpcInvocation) invocation).setInvoker(invoker);
        }
        try {
            // （详见下文）
            RpcResult result = (RpcResult) invoker.invoke(invocation);
            RpcContext.getServerContext().setAttachments(result.getAttachments());
            return result;
        } finally {
            // 清除上下文RpcContext中存储的“附件”信息
            RpcContext.getContext().clearAttachments();
        }
    }

@Override
    public Result invoke(final Invoker<?> invoker, final Invocation invocation) throws RpcException {
        // 此次调用是否是异步调用
        final boolean isAsync = RpcUtils.isAsync(invoker.getUrl(), invocation);

        fireInvokeCallback(invoker, invocation);
        // need to configure if there's return value before the invocation in order to help invoker to judge if it's
        // necessary to return future.
        Result result = invoker.invoke(invocation);
        if (isAsync) {
            // 异步调用
            asyncCallback(invoker, invocation);
        } else {
            // 同步调用（默认）
            syncCallback(invoker, invocation, result);
        }
        return result;
    }

@Override
    public Result invoke(Invocation invocation) throws RpcException {
        // 代码比较简单，没啥好说的
        return invoker.invoke(invocation);
    }

@Override
    public Result invoke(Invocation inv) throws RpcException {
        // if invoker is destroyed due to address refresh from registry, let's allow the current invoke to proceed
        // 上面的注释是指，在调用过程中如果invoker被更新了，则打印一个warn，并允许当前调用继续执行
        if (destroyed.get()) {
            logger.warn("Invoker for service " + this + " on consumer " + NetUtils.getLocalHost() + " is destroyed, "
                    + ", dubbo version is " + Version.getVersion() + ", this invoker should not be used any longer");
        }

        RpcInvocation invocation = (RpcInvocation) inv;
        invocation.setInvoker(this);
        // debug之后可以看到，attachment中存放的是接口信息
        if (attachment != null && attachment.size() > 0) {
            invocation.addAttachmentsIfAbsent(attachment);
        }
        Map<String, String> contextAttachments = RpcContext.getContext().getAttachments();
        if (contextAttachments != null && contextAttachments.size() != 0) {
            /**
             * invocation.addAttachmentsIfAbsent(context){@link RpcInvocation#addAttachmentsIfAbsent(Map)}should not be used here,
             * because the {@link RpcContext#setAttachment(String, String)} is passed in the Filter when the call is triggered
             * by the built-in retry mechanism of the Dubbo. The attachment to update RpcContext will no longer work, which is
             * a mistake in most cases (for example, through Filter to RpcContext output traceId and spanId and other information).
             */
            invocation.addAttachments(contextAttachments);
        }
        // 获取本次调用是否是异步，如果是异步，则在invocation对象中设置该属性
        if (getUrl().getMethodParameter(invocation.getMethodName(), Constants.ASYNC_KEY, false)) {
            invocation.setAttachment(Constants.ASYNC_KEY, Boolean.TRUE.toString());
        }
        // 代码跟进去不难发现，如果是异步调用，会将INVOKE_ID加入到附件中一并发送至服务提供方，在返回时，才能用INVOKE_ID匹配request
        RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
        try {
             // 发起调用（详见下文）
            return doInvoke(invocation);
        } catch (InvocationTargetException e) { // biz exception  调用异常处理
            Throwable te = e.getTargetException();
            if (te == null) {
                return new RpcResult(e);
            } else {
                if (te instanceof RpcException) {
                    ((RpcException) te).setCode(RpcException.BIZ_EXCEPTION);
                }
                return new RpcResult(te);
            }
        } catch (RpcException e) {
            if (e.isBiz()) {
                return new RpcResult(e);
            } else {
                throw e;
            }
        } catch (Throwable e) {
            return new RpcResult(e);
        }
    }

@Override
    protected Result doInvoke(final Invocation invocation) throws Throwable {
        RpcInvocation inv = (RpcInvocation) invocation;
        final String methodName = RpcUtils.getMethodName(invocation);
        // 设置调用信息
        inv.setAttachment(Constants.PATH_KEY, getUrl().getPath());
        inv.setAttachment(Constants.VERSION_KEY, version);

        // 获取客户端ExchangeClient信息（用来发送调用请求），包括url、client、refenceCount、ghostClientMap属性
        // url：中包记录dubbo、该provider的详细信息（version，interface，心跳频率等等）
        // client：服务器的信息（消费者和提供者）、长连接维持心跳的schedule线程池，此时也能看出dubbo是用netty构建的长连接
        ExchangeClient currentClient;
        if (clients.length == 1) {
            currentClient = clients[0];
        } else {
            currentClient = clients[index.getAndIncrement() % clients.length];
        }
        try {
            boolean isAsync = RpcUtils.isAsync(getUrl(), invocation);// 是否异步
            boolean isOneway = RpcUtils.isOneway(getUrl(), invocation);// 该项配置是指，本次调用是否为单向调用
            int timeout = getUrl().getMethodParameter(methodName, Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT);
            if (isOneway) {
                boolean isSent = getUrl().getMethodParameter(methodName, Constants.SENT_KEY, false);
                currentClient.send(inv, isSent);// 如果是单向调用，则send，本次调用结束
                RpcContext.getContext().setFuture(null);
                return new RpcResult();
            } else if (isAsync) {
                ResponseFuture future = currentClient.request(inv, timeout);
                RpcContext.getContext().setFuture(new FutureAdapter<Object>(future));
                return new RpcResult();
            } else {
                RpcContext.getContext().setFuture(null);
                // 同步则request，并返回一个ResponseFuture对象，执行get获取响应对象result
                // 通过Condition.await()方法等待provider响应，待响应到达后，执行condition.signal()方法
                // request代码详见下文
                return (Result) currentClient.request(inv, timeout).get();
            }
        } catch (TimeoutException e) {
            throw new RpcException(RpcException.TIMEOUT_EXCEPTION, "Invoke remote method timeout. method: " + invocation.getMethodName() + ", provider: " + getUrl() + ", cause: " + e.getMessage(), e);
        } catch (RemotingException e) {
            throw new RpcException(RpcException.NETWORK_EXCEPTION, "Failed to invoke remote method: " + invocation.getMethodName() + ", provider: " + getUrl() + ", cause: " + e.getMessage(), e);
        }
    }

@Override
    public ResponseFuture request(Object request, int timeout) throws RemotingException {
        // 如果该channel被关闭则抛异常
        if (closed) {
            throw new RemotingException(this.getLocalAddress(), null, "Failed to send request " + request + ", cause: The channel " + this + " is closed!");
        }
        // create request.   创建request对象并作包装
        Request req = new Request();
        req.setVersion(Version.getProtocolVersion());
        req.setTwoWay(true);// 设置为双向（本次调用需要有响应）
        req.setData(request);
        // 注册future，用于获取响应
        DefaultFuture future = new DefaultFuture(channel, req, timeout);
        try {
            channel.send(req);
        } catch (RemotingException e) {
            future.cancel();// 发生异常则cancel
            throw e;
        }
        return future;
    }

@Override
    public void send(Object message, boolean sent) throws RemotingException {
        super.send(message, sent);// 判断该channel是否被关闭

        boolean success = true;
        int timeout = 0;
        try {
            ChannelFuture future = channel.write(message);// 发送信息
            if (sent) {
                 // 获取超时时间，默认1s
                timeout = getUrl().getPositiveParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT);
                success = future.await(timeout);// 等待响应
            }
            Throwable cause = future.getCause();// 异常处理
            if (cause != null) {
                throw cause;
            }
        } catch (Throwable e) {
            throw new RemotingException(this, "Failed to send message " + message + " to " + getRemoteAddress() + ", cause: " + e.getMessage(), e);
        }

        if (!success) {
            throw new RemotingException(this, "Failed to send message " + message + " to " + getRemoteAddress()
                    + "in timeout(" + timeout + "ms) limit");
        }
    }