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Dubbo服务调用过程

林肯公园_97cc 2022-03-30 阅读 60
DubboJava后端分布式

前几篇文章讲述了 Dubbo 的注册和消费的流程、今天继续接着说下调用的流程(只谈及单注册中心、多注册中心只是前面多了一步、根据区域或者配置选择出其中一个注册中心而已)

image-20220228215213474

我们在消费者端调用就是该代理工厂返回的对象

@Override
public <T> T getProxy(Invoker<T> invoker, boolean generic) throws RpcException {
    Set<Class<?>> interfaces = new HashSet<>();
    String config = invoker.getUrl().getParameter(INTERFACES);
    if (config != null && config.length() > 0) {
        String[] types = COMMA_SPLIT_PATTERN.split(config);
        for (String type : types) {
            // TODO can we load successfully for a different classloader?.
            interfaces.add(ReflectUtils.forName(type));
        }
    }

    if (generic) {
			.........
    }

    interfaces.add(invoker.getInterface());
    interfaces.addAll(Arrays.asList(INTERNAL_INTERFACES));
    return getProxy(invoker, interfaces.toArray(new Class<?>[0]));
}

JavassistProxyFactory

@Override
@SuppressWarnings("unchecked")
public <T> T getProxy(Invoker<T> invoker, Class<?>[] interfaces) {
  return (T) Proxy.getProxy(interfaces).newInstance(new InvokerInvocationHandler(invoker));
}

DubboProtocol

@Override
public <T> Invoker<T> protocolBindingRefer(Class<T> serviceType, URL url) throws RpcException {
  optimizeSerialization(url);

  // create rpc invoker.
  DubboInvoker<T> invoker = new DubboInvoker<T>(serviceType, url, getClients(url), invokers);
  invokers.add(invoker);

  return invoker;
}
public Class<T> getInterface() {
    return type;
}

这个就是我们熟悉的 JDK 动态代理。InvokerInvocationHandler 的 invoke

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (method.getDeclaringClass() == Object.class) {
        return method.invoke(invoker, args);
    }
    String methodName = method.getName();
    Class<?>[] parameterTypes = method.getParameterTypes();
    if (parameterTypes.length == 0) {
        if ("toString".equals(methodName)) {
            return invoker.toString();
        } else if ("$destroy".equals(methodName)) {
            invoker.destroy();
            return null;
        } else if ("hashCode".equals(methodName)) {
            return invoker.hashCode();
        }
    } else if (parameterTypes.length == 1 && "equals".equals(methodName)) {
        return invoker.equals(args[0]);
    }
    RpcInvocation rpcInvocation = new RpcInvocation(method, invoker.getInterface().getName(), args);
    String serviceKey = invoker.getUrl().getServiceKey();
    rpcInvocation.setTargetServiceUniqueName(serviceKey);
  
    if (consumerModel != null) {
        rpcInvocation.put(Constants.CONSUMER_MODEL, consumerModel);
        rpcInvocation.put(Constants.METHOD_MODEL, consumerModel.getMethodModel(method));
    }

    return invoker.invoke(rpcInvocation).recreate();
}

这个 Invoker 我们从消费者启动流程中可以知道、最外层是 MockClusterInvoker

用于服务的降级熔断

  • 正常调用
  • 熔断、直接使用 mock 相关配置
  • 降级、服务提供方异常后使用 mock 相关配置
@Override
public Result invoke(Invocation invocation) throws RpcException {
    Result result = null;

    String value = getUrl().getMethodParameter(invocation.getMethodName(), MOCK_KEY, Boolean.FALSE.toString()).trim();
    if (value.length() == 0 || "false".equalsIgnoreCase(value)) {
        //no mock
        result = this.invoker.invoke(invocation);
    } else if (value.startsWith("force")) {
        //force:direct mock
        result = doMockInvoke(invocation, null);
    } else {
        //fail-mock
        try {
            result = this.invoker.invoke(invocation);

            //fix:#4585
            if(result.getException() != null && result.getException() instanceof RpcException){
                RpcException rpcException= (RpcException)result.getException();
                if(rpcException.isBiz()){
                    throw  rpcException;
                }else {
                    result = doMockInvoke(invocation, rpcException);
                }
            }

        } catch (RpcException e) {
            if (e.isBiz()) {
                throw e;
            }
            result = doMockInvoke(invocation, e);
        }
    }
    return result;
}

private Result doMockInvoke(Invocation invocation, RpcException e) {
    Result result = null;
    Invoker<T> minvoker;

    List<Invoker<T>> mockInvokers = selectMockInvoker(invocation);
    if (CollectionUtils.isEmpty(mockInvokers)) {
        minvoker = (Invoker<T>) new MockInvoker(getUrl(), directory.getInterface());
    } else {
        minvoker = mockInvokers.get(0);
    }
    try {
        result = minvoker.invoke(invocation);
    } catch (RpcException me) {
        if (me.isBiz()) {
            result = AsyncRpcResult.newDefaultAsyncResult(me.getCause(), invocation);
        } else {
            throw new RpcException(me.getCode(), getMockExceptionMessage(e, me), me.getCause());
        }
    } catch (Throwable me) {
        throw new RpcException(getMockExceptionMessage(e, me), me.getCause());
    }
    return result;
}

再看一下他是如何选择出 invoker 的

private List<Invoker<T>> selectMockInvoker(Invocation invocation) {
    List<Invoker<T>> invokers = null;
    //TODO generic invoker？
    if (invocation instanceof RpcInvocation) {
        //Note the implicit contract (although the description is added to the interface declaration, but extensibility is a problem. The practice placed in the attachment needs to be improved)
        ((RpcInvocation) invocation).setAttachment(INVOCATION_NEED_MOCK, Boolean.TRUE.toString());
        //directory will return a list of normal invokers if Constants.INVOCATION_NEED_MOCK is present in invocation, otherwise, a list of mock invokers will return.
        try {
            invokers = directory.list(invocation);
        } catch (RpcException e) {
            if (logger.isInfoEnabled()) {
                logger.info("Exception when try to invoke mock. Get mock invokers error for service:"
                        + getUrl().getServiceInterface() + ", method:" + invocation.getMethodName()
                        + ", will construct a new mock with 'new MockInvoker()'.", e);
            }
        }
    }
    return invokers;
}

我们再来看一下 MockInvokersSelector、入参 invokers 是我们在 RegistryDireotry 中正常的 invoker

@Override
public <T> List<Invoker<T>> route(final List<Invoker<T>> invokers,
                                  URL url, final Invocation invocation) throws RpcException {
    if (CollectionUtils.isEmpty(invokers)) {
        return invokers;
    }

    if (invocation.getObjectAttachments() == null) {
        return getNormalInvokers(invokers);
    } else {
        String value = (String) invocation.getObjectAttachments().get(INVOCATION_NEED_MOCK);
        if (value == null) {
            return getNormalInvokers(invokers);
        } else if (Boolean.TRUE.toString().equalsIgnoreCase(value)) {
            return getMockedInvokers(invokers);
        }
    }
    return invokers;
}

因为我们设置了 INVOCATION_NEED_MOCK 的值为 true

private <T> List<Invoker<T>> getMockedInvokers(final List<Invoker<T>> invokers) {
    if (!hasMockProviders(invokers)) {
        return null;
    }
    List<Invoker<T>> sInvokers = new ArrayList<Invoker<T>>(1);
    for (Invoker<T> invoker : invokers) {
        if (invoker.getUrl().getProtocol().equals(MOCK_PROTOCOL)) {
            sInvokers.add(invoker);
        }
    }
    return sInvokers;
}

找到以 mock 作为协议的 invoker

如果没有的话、则会到上方调用方那里、自己去创建一个 MockInvoker。然后根据配置信息返回

if (CollectionUtils.isEmpty(mockInvokers)) {
    minvoker = (Invoker<T>) new MockInvoker(getUrl(), directory.getInterface());

image-20220301074846119

如果不是 mock 的话、我们再进入到 org.apache.dubbo.rpc.cluster.support.wrapper.AbstractCluster.InterceptorInvokerNode 的 invoke 方法中

@Override
public Result invoke(Invocation invocation) throws RpcException {
    Result asyncResult;
    try {
        interceptor.before(next, invocation);
        asyncResult = interceptor.intercept(next, invocation);
    } catch (Exception e) {
        // onError callback
        if (interceptor instanceof ClusterInterceptor.Listener) {
            ClusterInterceptor.Listener listener = (ClusterInterceptor.Listener) interceptor;
            listener.onError(e, clusterInvoker, invocation);
        }
        throw e;
    } finally {
        interceptor.after(next, invocation);
    }
    return asyncResult.whenCompleteWithContext((r, t) -> {
        // onResponse callback
        if (interceptor instanceof ClusterInterceptor.Listener) {
            ClusterInterceptor.Listener listener = (ClusterInterceptor.Listener) interceptor;
            if (t == null) {
                listener.onMessage(r, clusterInvoker, invocation);
            } else {
                listener.onError(t, clusterInvoker, invocation);
            }
        }
    });
}

这里的拦截器最终会调用 FailoverClusterInvoker 的 invoker 方法

FailoverClusterInvoker 的父类 AbstractClusterInvoker

@Override
public Result invoke(final Invocation invocation) throws RpcException {
    checkWhetherDestroyed();

    // binding attachments into invocation.
    Map<String, Object> contextAttachments = RpcContext.getContext().getObjectAttachments();
    if (contextAttachments != null && contextAttachments.size() != 0) {
        ((RpcInvocation) invocation).addObjectAttachments(contextAttachments);
    }

    List<Invoker<T>> invokers = list(invocation);
    LoadBalance loadbalance = initLoadBalance(invokers, invocation);
    RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
    return doInvoke(invocation, invokers, loadbalance);
}

这里的 list 会默认返回所有注册的服务提供者列表

protected List<Invoker<T>> list(Invocation invocation) throws RpcException {
    return directory.list(invocation);
}

initLoadBalance 则会选择出一个负载均衡策略、默认是随机

protected LoadBalance initLoadBalance(List<Invoker<T>> invokers, Invocation invocation) {
    if (CollectionUtils.isNotEmpty(invokers)) {
        return ExtensionLoader.getExtensionLoader(LoadBalance.class).getExtension(invokers.get(0).getUrl()
                .getMethodParameter(RpcUtils.getMethodName(invocation), LOADBALANCE_KEY, DEFAULT_LOADBALANCE));
    } else {
        return ExtensionLoader.getExtensionLoader(LoadBalance.class).getExtension(DEFAULT_LOADBALANCE);
    }
}

然后进入到 FailoverClusterInvoker 的 doInvoke 中

@Override
@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);
    String methodName = RpcUtils.getMethodName(invocation);
    int len = getUrl().getMethodParameter(methodName, RETRIES_KEY, 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++) {
        if (i > 0) {
            checkWhetherDestroyed();
            copyInvokers = list(invocation);
            // check again
            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);
            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.getCode()......);
}

这个就是从一堆 Invoker 中选出一个、这里涉及到失败重试的机制、如果不是业务异常、那么就会选择另一个 Invoker 进行重试

protected Invoker<T> select(LoadBalance loadbalance, Invocation invocation,
                            List<Invoker<T>> invokers, List<Invoker<T>> selected) throws RpcException {

    if (CollectionUtils.isEmpty(invokers)) {
        return null;
    }
    String methodName = invocation == null ? StringUtils.EMPTY_STRING : invocation.getMethodName();
    boolean sticky = invokers.get(0).getUrl()
            .getMethodParameter(methodName, CLUSTER_STICKY_KEY, DEFAULT_CLUSTER_STICKY);

    //ignore overloaded method
    if (stickyInvoker != null && !invokers.contains(stickyInvoker)) {
        stickyInvoker = null;
    }
    //ignore concurrency problem
    if (sticky && stickyInvoker != null && (selected == null || !selected.contains(stickyInvoker))) {
        if (availablecheck && stickyInvoker.isAvailable()) {
            return stickyInvoker;
        }
    }
    Invoker<T> invoker = doSelect(loadbalance, invocation, invokers, selected);
    if (sticky) {
        stickyInvoker = invoker;
    }
    return invoker;
}

private Invoker<T> doSelect(LoadBalance loadbalance, Invocation invocation,
                            List<Invoker<T>> invokers, List<Invoker<T>> selected) throws RpcException {

    if (CollectionUtils.isEmpty(invokers)) {
        return null;
    }
    if (invokers.size() == 1) {
        return invokers.get(0);
    }
    Invoker<T> invoker = loadbalance.select(invokers, getUrl(), invocation);
    //If the `invoker` is in the  `selected` or invoker is unavailable && availablecheck is true, reselect.
    if ((selected != null && selected.contains(invoker))
            || (!invoker.isAvailable() && getUrl() != null && availablecheck)) {
        try {
            Invoker<T> rInvoker = reselect(loadbalance, invocation, invokers, selected, availablecheck);
            if (rInvoker != null) {
                invoker = rInvoker;
            } else {
                int index = invokers.indexOf(invoker);
                try {
                    //Avoid collision
                    invoker = invokers.get((index + 1) % invokers.size());
                } catch (Exception e) {
                }
            }
        } catch (Throwable t) {
        }
    }
    return invoker;
}

private Invoker<T> reselect(LoadBalance loadbalance, Invocation invocation,
                            List<Invoker<T>> invokers, List<Invoker<T>> selected, boolean availablecheck) throws RpcException {

    //Allocating one in advance, this list is certain to be used.
    List<Invoker<T>> reselectInvokers = new ArrayList<>(
            invokers.size() > 1 ? (invokers.size() - 1) : invokers.size());

    // First, try picking a invoker not in `selected`.
    for (Invoker<T> invoker : invokers) {
        if (availablecheck && !invoker.isAvailable()) {
            continue;
        }

        if (selected == null || !selected.contains(invoker)) {
            reselectInvokers.add(invoker);
        }
    }

    if (!reselectInvokers.isEmpty()) {
        return loadbalance.select(reselectInvokers, getUrl(), invocation);
    }

    // Just pick an available invoker using loadbalance policy
    if (selected != null) {
        for (Invoker<T> invoker : selected) {
            if ((invoker.isAvailable()) // available first
                    && !reselectInvokers.contains(invoker)) {
                reselectInvokers.add(invoker);
            }
        }
    }
    if (!reselectInvokers.isEmpty()) {
        return loadbalance.select(reselectInvokers, getUrl(), invocation);
    }

    return null;
}

逻辑也是比较简单、有没调用过的就用没调用过的、没有只好选择已经调用过但是是可用状态的

我们继续往下调用。这个是 RegistryDiretory 的部分代码、详细可以看上几篇文章

invoker = new InvokerDelegate<>(protocol.refer(serviceType, url), url, providerUrl);

InvokerDelegate 其实就是个代理类、啥都不做

@Override
public Result invoke(Invocation invocation) throws RpcException {
    return invoker.invoke(invocation);
}

protocol.refer(serviceType, url) 则会被几个 Wrapper 类所装饰

ProtocolFilterWrapper 会调用所有的 Filter 接口方法、然后才回调用下一个 Invoker

ListenerInvokerWrapper 则是将 invoker 给到 listener、看实现类基本是没啥用的这个 Listener

经过完 Wrapper 之后、来到了 AsyncToSyncInvoker

@Override
public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
    return new AsyncToSyncInvoker<>(protocolBindingRefer(type, url));
}

顾名思义、就是一步转同步的

@Override
public Result invoke(Invocation invocation) throws RpcException {
    Result asyncResult = invoker.invoke(invocation);

    try {
        if (InvokeMode.SYNC == ((RpcInvocation) invocation).getInvokeMode()) {
            asyncResult.get(Integer.MAX_VALUE, TimeUnit.MILLISECONDS);
        }
    } catch (InterruptedException e) {
      .....
    }
    return asyncResult;
}

最后终于来到了 DubboInvoker

@Override
public Result invoke(Invocation inv) throws RpcException {
    RpcInvocation invocation = (RpcInvocation) inv;
    invocation.setInvoker(this);
    if (CollectionUtils.isNotEmptyMap(attachment)) {
        invocation.addObjectAttachmentsIfAbsent(attachment);
    }

    Map<String, Object> contextAttachments = RpcContext.getContext().getObjectAttachments();
    if (CollectionUtils.isNotEmptyMap(contextAttachments)) {
        invocation.addObjectAttachments(contextAttachments);
    }

    invocation.setInvokeMode(RpcUtils.getInvokeMode(url, invocation));
    RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);

    AsyncRpcResult asyncResult;
    try {
        asyncResult = (AsyncRpcResult) doInvoke(invocation);
    } catch (InvocationTargetException e) { // biz exception
			.......
    }
    RpcContext.getContext().setFuture(new FutureAdapter(asyncResult.getResponseFuture()));
    return asyncResult;
}

这里就通过 Netty 与 provider 进行通信了。currentClient.request

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

    ExchangeClient currentClient;
    if (clients.length == 1) {
        currentClient = clients[0];
    } else {
        currentClient = clients[index.getAndIncrement() % clients.length];
    }
    try {
        boolean isOneway = RpcUtils.isOneway(getUrl(), invocation);
        int timeout = calculateTimeout(invocation, methodName);
        if (isOneway) {
            boolean isSent = getUrl().getMethodParameter(methodName, Constants.SENT_KEY, false);
            currentClient.send(inv, isSent);
            return AsyncRpcResult.newDefaultAsyncResult(invocation);
        } else {
            ExecutorService executor = getCallbackExecutor(getUrl(), inv);
            CompletableFuture<AppResponse> appResponseFuture =
                    currentClient.request(inv, timeout, executor).thenApply(obj -> (AppResponse) obj);
            // save for 2.6.x compatibility, for example, TraceFilter in Zipkin uses com.alibaba.xxx.FutureAdapter
            FutureContext.getContext().setCompatibleFuture(appResponseFuture);
            AsyncRpcResult result = new AsyncRpcResult(appResponseFuture, inv);
            result.setExecutor(executor);
            return result;
        }
    } catch (TimeoutException e) {
       .....
    }
}

整个调用链的流程大致就是如此、整个流程事实上就是消费者端创建代理的过程

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