远程调用
服务消费者
Consumer远程调用流程主要可以用一下的这张流程图表示
流程图
Dubbo服务消费者服务调用流程图.png
主要流程
主要为以下的几个步骤
- 调用对应的代理类
- 被InvokerInvacationHandler拦截
- ClusterInvoker经过路由过滤，负载均衡，选择其中一个Invoker，发起远程调用（带请求ID）
相关源码
public class JavassistProxyFactory extends AbstractProxyFactory {
@Override
@SuppressWarnings("unchecked")
public <T> T getProxy(Invoker<T> invoker, Class<?>[] interfaces) {
// InvokerInvocationHandler （重点关注）
// 远程调用时，调用的方法会被 InvokerInvocationHandler 拦截
return (T) Proxy.getProxy(interfaces).newInstance(new InvokerInvocationHandler(invoker));
}
@Override
public <T> Invoker<T> getInvoker(T proxy, Class<T> type, URL url) {
// TODO Wrapper cannot handle this scenario correctly: the classname contains '$'
final Wrapper wrapper = Wrapper.getWrapper(proxy.getClass().getName().indexOf('$') < 0 ? proxy.getClass() : type);
return new AbstractProxyInvoker<T>(proxy, type, url) {
@Override
protected Object doInvoke(T proxy, String methodName,
Class<?>[] parameterTypes,
Object[] arguments) throws Throwable {
return wrapper.invokeMethod(proxy, methodName, parameterTypes, arguments);
}
};
}
org.apache.dubbo.rpc.proxy.InvokerInvocationHandler#invoke
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (method.getDeclaringClass() == Object.class) {
return method.invoke(invoker, args);
}
// 获取调用的远程方法名
String methodName = method.getName();
// 获取参数
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]);
}
// 构建一个dubbo rpc invocation
RpcInvocation rpcInvocation = new RpcInvocation(method, invoker.getInterface().getName(), protocolServiceKey, args);
String serviceKey = invoker.getUrl().getServiceKey();
rpcInvocation.setTargetServiceUniqueName(serviceKey);
// invoker.getUrl() returns consumer url.
RpcContext.setRpcContext(invoker.getUrl());
if (consumerModel != null) {
rpcInvocation.put(Constants.CONSUMER_MODEL, consumerModel);
rpcInvocation.put(Constants.METHOD_MODEL, consumerModel.getMethodModel(method));
}
// 远程调用
return invoker.invoke(rpcInvocation).recreate();
}
@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);
}
// 实际上就是directroy.list 通过方法名寻找invokers 里面回去做一些过滤 获取过滤后的invoke列表
List<Invoker<T>> invokers = list(invocation);
// 根据@SPI选择负载均衡的策略
LoadBalance loadbalance = initLoadBalance(invokers, invocation);
RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
return doInvoke(invocation, invokers, loadbalance); // 调用子类的方法
}
@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++) {
//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
checkInvokers(copyInvokers, invocation);
}
// 根据负载均衡规则找出一个invoker
Invoker<T> invoker = select(loadbalance, invocation, copyInvokers, invoked);
invoked.add(invoker);
RpcContext.getContext().setInvokers((List) invoked);
try {
// 远程调用(每次请求都有一个唯一的ID)
Result result = invoker.invoke(invocation);
if (le != null && logger.isWarnEnabled()) {
logger.warn("Although retry the method " + methodName
+ " 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.getCode(), "Failed to invoke the method "
+ methodName + " 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.getMessage(), le.getCause() != null ? le.getCause() : le);
}
服务提供者
在Consumer发起调用后，Provider就需要去处理客户端的请求了。
消费端发起TCP链接并完成后，服务提供方的NettyServer的connected方法会被激活。摘自 “深度剖析Apache Dubbo核心技术内幕”
流程图
Dubbo服务器提供者处理流程图.png
主要流程
- 服务端的NettyServer处理请求，最终会调用到DubboProtol#reply
- 根据客户端的请求，从ExportedMap中选择对应的Invoker
- 调用Invoker具体业务类的方法
- 返回处理结果
相关源码
NettyServer的Handler处理请求
@Override
public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
NettyChannel channel = NettyChannel.getOrAddChannel(ctx.getChannel(), url, handler);
try {
if (channel != null) {
channels.put(NetUtils.toAddressString((InetSocketAddress) ctx.getChannel().getRemoteAddress()), channel);
}
handler.connected(channel);
} finally {
NettyChannel.removeChannelIfDisconnected(ctx.getChannel());
}
if (logger.isInfoEnabled()) {
logger.info("The connection between " + channel.getRemoteAddress() + " and " + channel.getLocalAddress() + " is established");
}
}
AllChannelHandler
@Override
public void connected(Channel channel) throws RemotingException {
ExecutorService executor = getExecutorService();
try {
// 封装成ChannelEventRunnable，丢到线程中处理
executor.execute(new ChannelEventRunnable(channel, handler, ChannelState.CONNECTED));
} catch (Throwable t) {
throw new ExecutionException("connect event", channel, getClass() + " error when process connected event .", t);
}
}
HeaderExchangeHandler
void handleRequest(final ExchangeChannel channel, Request req) throws RemotingException {
// 通过请求id，构建一个Response
Response res = new Response(req.getId(), req.getVersion());
if (req.isBroken()) {
// 获取请求信息 方法名之类的
Object data = req.getData();
String msg;
if (data == null) {
msg = null;
} else if (data instanceof Throwable) {
msg = StringUtils.toString((Throwable) data);
} else {
msg = data.toString();
}
res.setErrorMessage("Fail to decode request due to: " + msg);
res.setStatus(Response.BAD_REQUEST);
channel.send(res);
return;
}
// find handler by message class.
Object msg = req.getData();
try {
// 最终调用 DubboProtocol reply
CompletionStage<Object> future = handler.reply(channel, msg);
future.whenComplete((appResult, t) -> {
try {
if (t == null) {
res.setStatus(Response.OK);
res.setResult(appResult);
} else {
res.setStatus(Response.SERVICE_ERROR);
res.setErrorMessage(StringUtils.toString(t));
}
channel.send(res);
} catch (RemotingException e) {
logger.warn("Send result to consumer failed, channel is " + channel + ", msg is " + e);
}
});
} catch (Throwable e) {
res.setStatus(Response.SERVICE_ERROR);
res.setErrorMessage(StringUtils.toString(e));
channel.send(res);
}
}
DubboProtocol
private ExchangeHandler requestHandler = new ExchangeHandlerAdapter() {
@Override
public CompletableFuture<Object> reply(ExchangeChannel channel, Object message) throws RemotingException {
if (!(message instanceof Invocation)) {
throw new RemotingException(channel, "Unsupported request: "
+ (message == null ? null : (message.getClass().getName() + ": " + message))
+ ", channel: consumer: " + channel.getRemoteAddress() + " --> provider: " + channel.getLocalAddress());
}
Invocation inv = (Invocation) message;
// 根据inv获取Invoker 去exporterMap中找
Invoker<?> invoker = getInvoker(channel, inv);
// need to consider backward-compatibility if it's a callback
if (Boolean.TRUE.toString().equals(inv.getObjectAttachments().get(IS_CALLBACK_SERVICE_INVOKE))) {
String methodsStr = invoker.getUrl().getParameters().get("methods");
boolean hasMethod = false;
if (methodsStr == null || !methodsStr.contains(",")) {
hasMethod = inv.getMethodName().equals(methodsStr);
} else {
String[] methods = methodsStr.split(",");
for (String method : methods) {
if (inv.getMethodName().equals(method)) {
hasMethod = true;
break;
}
}
}
if (!hasMethod) {
logger.warn(new IllegalStateException("The methodName " + inv.getMethodName()
+ " not found in callback service interface ,invoke will be ignored."
+ " please update the api interface. url is:"
+ invoker.getUrl()) + " ,invocation is :" + inv);
return null;
}
}
RpcContext.getContext().setRemoteAddress(channel.getRemoteAddress());
// 调用对应的invoke方法（最终wrapper.invokeMethod，参考服务暴露文档）
Result result = invoker.invoke(inv);
return result.thenApply(Function.identity());
}
总结
总结为一句话就是：客户端在发起远程调用时，具体的代理类会被InvokerInvacationHandler拦截，在这里面根据一些条件和负载均衡策略，选择出其中一个符合条件的Invoker，进行远程调用。提供者收到请求后，会从ExpoterMap中选择对应的Invoker（Wrapper包装），最终调用到具体的实现类。处理完请求后将结果返回。返回后客户端根据之前传过去的请求ID，找到之前的请求，然后再进行自己的业务处理
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