Dubbo原始碼理解（3） 消費者呼叫過程
阿新 • • 發佈：2018-11-28
小弟一直苦思 consumer 與provider 到底是怎麼通訊的呢，與是從網上找了一篇，覺得寫得很靠譜。自己就算總結，也未必有這個好，所以記錄下來！！
消費者呼叫流程涉及到消費者端和生產者端的互動，所以將分為三個部分來講解，分別是
-消費者發起呼叫請求
-生產者響應呼叫請求
-消費者獲取呼叫結果
消費者發起呼叫請求
之前文章中講過消費者初始化時最後返回的是一個InvokerInvocationHandler的代理物件，根據動態代理的原理，DUBBO介面的方法呼叫都會由invoke方法代理，我們來看一下其實現
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]); } return invoker.invoke(new RpcInvocation(method, args)).recreate(); }
正常情況下的方法呼叫會走invoker.invoke(new RpcInvocation(method, args)).recreate()這個分支，首先來看new RpcInvocation(method, args)
public RpcInvocation(Method method, Object[] arguments) { this(method.getName(), method.getParameterTypes(), arguments, null, null); } public RpcInvocation(String methodName, Class<?>[] parameterTypes, Object[] arguments, Map<String, String> attachments, Invoker<?> invoker) { this.methodName = methodName; this.parameterTypes = parameterTypes == null ? new Class<?>[0] : parameterTypes; this.arguments = arguments == null ? new Object[0] : arguments; this.attachments = attachments == null ? new HashMap<String, String>() : attachments; this.invoker = invoker; }
非常簡單的一個初始化賦值操作，就不做過多講解了，接著回頭看invoker.invoke(new RpcInvocation(method, args))方法，這裡的invoker之前也說過了，是一個通過SPI機制生成的物件，以預設設定的引數failover為例，這裡的invoker就是一個MockClusterInvoker物件中包含了一個FailoverClusterInvoker物件引用的類似鏈式的物件，那麼我們來詳細看看MockClusterInvoker的invoke方法
public Result invoke(Invocation invocation) throws RpcException { Result result = null; //獲取mock屬性的值，沒有配置，預設false String value = directory.getUrl().getMethodParameter(invocation.getMethodName(), Constants.MOCK_KEY, Boolean.FALSE.toString()).trim(); if (value.length() == 0 || value.equalsIgnoreCase("false")){ //no mock result = this.invoker.invoke(invocation); } else if (value.startsWith("force")) { if (logger.isWarnEnabled()) { logger.info("force-mock: " + invocation.getMethodName() + " force-mock enabled , url : " + directory.getUrl()); } //force:direct mock result = doMockInvoke(invocation, null); } else { //fail-mock try { result = this.invoker.invoke(invocation); }catch (RpcException e) { if (e.isBiz()) { throw e; } else { if (logger.isWarnEnabled()) { logger.info("fail-mock: " + invocation.getMethodName() + " fail-mock enabled , url : " + directory.getUrl(), e); } result = doMockInvoke(invocation, e); } } } return result; }
當沒有配置mock值時，value值得到的是預設值false，會去執行result = this.invoker.invoke(invocation)，this.invoker剛才提到過了是一個FailoverClusterInvoker型別的物件，但該物件並沒有實現invoke方法，實際上該方法是繼承自父類AbstractClusterInvoker的，來看一下
public Result invoke(final Invocation invocation) throws RpcException {
checkWheatherDestoried();
LoadBalance loadbalance;
List<Invoker<T>> invokers = list(invocation);
if (invokers != null && invokers.size() > 0) {
loadbalance = ExtensionLoader.getExtensionLoader(LoadBalance.class).getExtension(invokers.get(0).getUrl()
.getMethodParameter(invocation.getMethodName(),Constants.LOADBALANCE_KEY, Constants.DEFAULT_LOADBALANCE));
} else {
loadbalance = ExtensionLoader.getExtensionLoader(LoadBalance.class).getExtension(Constants.DEFAULT_LOADBALANCE);
}
//非同步操作預設新增invocation id
RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
return doInvoke(invocation, invokers, loadbalance);
}
這裡的list(invocation)方法根據invocation中的引數來獲取所有的invoker列表，就不深入講了，接著來看loadbalance物件的生成，loadbalance物件根據SPI機制生成，具體實現由loadbalance引數決定，也就是具體的負載均衡策略，DUBBO提供的實現有random、roundrobin、leastactive、consistenthash四種，其中沒有根據服務端負載進行調節的策略。其中預設實現為random，生成的loadbalance就是一個RandomLoadBalance的物件。本次只分析同步的介面呼叫方式，跳過RpcUtils.attachInvocationIdIfAsync，接著看doInvoke(invocation, invokers, loadbalance)方法，該方法實現在FailoverClusterInvoker中
public Result doInvoke(Invocation invocation, final List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
List<Invoker<T>> copyinvokers = invokers;
//檢查invokers是否為空
checkInvokers(copyinvokers, invocation);
//獲取重試次數
int len = getUrl().getMethodParameter(invocation.getMethodName(), Constants.RETRIES_KEY, Constants.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++) {
//重試時，進行重新選擇，避免重試時invoker列表已發生變化.
//注意：如果列表發生了變化，那麼invoked判斷會失效，因為invoker示例已經改變
if (i > 0) {
checkWheatherDestoried();
//獲得InvokerWrapper的List
copyinvokers = list(invocation);
//重新檢查一下
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);
if (le != null && logger.isWarnEnabled()) {
logger.warn("");
}
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
/**
* 略去部分程式碼
*/
}
這裡select(loadbalance, invocation, copyinvokers, invoked)方法根據傳入的loadbalance物件挑選出一個執行用的invoker，裡面呼叫鏈較深，在此不做詳細分析。最終將通過invoker.invoke(invocation)進行呼叫並返回一個Result型別的物件，也就是最終的執行結果，這裡的invoker物件是InvokerWrapper的例項，該例項引用了一個ListenerInvokerWrapper的例項，接著又鏈式引用了AbstractInvoker的例項，因此最終執行的invoke方法在AbstractInvoker中，來看一下
public Result invoke(Invocation inv) throws RpcException {
if(destroyed) {
throw new RpcException("略");
}
RpcInvocation invocation = (RpcInvocation) inv;
invocation.setInvoker(this);
if (attachment != null && attachment.size() > 0) {
invocation.addAttachmentsIfAbsent(attachment);
}
Map<String, String> context = RpcContext.getContext().getAttachments();
if (context != null) {
invocation.addAttachmentsIfAbsent(context);
}
if (getUrl().getMethodParameter(invocation.getMethodName(), Constants.ASYNC_KEY, false)){
invocation.setAttachment(Constants.ASYNC_KEY, Boolean.TRUE.toString());
}
//非同步操作預設新增invocation id
RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
try {
return doInvoke(invocation);
} catch (InvocationTargetException e) { // biz exception
/**
* 略去部分程式碼
*/
}
}
這裡的關鍵方法是doInvoke(invocation)，其實現在具體的Invoker實現類中，這裡我們採用的是預設的dubbo協議，所以實現類為DubboInvoker，來看看其doInvoke方法
@Override
protected Result doInvoke(final Invocation invocation) throws Throwable {
RpcInvocation inv = (RpcInvocation) invocation;
final String methodName = RpcUtils.getMethodName(invocation);
inv.setAttachment(Constants.PATH_KEY, getUrl().getPath());
inv.setAttachment(Constants.VERSION_KEY, version);
ExchangeClient currentClient;
//消費者初始化時與服務端建立的連線
if (clients.length == 1) {
currentClient = clients[0];
} else {
currentClient = clients[index.getAndIncrement() % clients.length];
}
try {
boolean isAsync = RpcUtils.isAsync(getUrl(), invocation);
boolean isOneway = RpcUtils.isOneway(getUrl(), invocation);
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);
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);
return (Result) currentClient.request(inv, timeout).get();
}
/**
* 略去部分程式碼
*/
}
這裡的isOneway和isAsync兩個標誌位分別區分單向呼叫(不在乎呼叫結果)和非同步呼叫，這裡我們分析同步呼叫的流程，這裡的currentClient是一個ReferenceCountExchangeClient型別的物件
public ResponseFuture request(Object request) throws RemotingException {
return client.request(request);
}
這裡的client是一個HeaderExchangeClient型別的物件，
public ResponseFuture request(Object request) throws RemotingException {
return channel.request(request);
}
這裡的channel是一個HeaderExchangeChannel型別的物件，繼續跟進去
public ResponseFuture request(Object request) throws RemotingException {
return request(request, channel.getUrl().getPositiveParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT));
}
public ResponseFuture request(Object request, int timeout) throws RemotingException {
if (closed) {
throw new RemotingException(this.getLocalAddress(), null, "Failed to send request " + request + ", cause: The channel " + this + " is closed!");
}
// create request.
Request req = new Request();
req.setVersion("2.0.0");
req.setTwoWay(true);
req.setData(request);
DefaultFuture future = new DefaultFuture(channel, req, timeout);
try{
channel.send(req);
}catch (RemotingException e) {
future.cancel();
throw e;
}
return future;
}
這裡的request方法自己又進行了一次內部呼叫，可以看到具體實現時建立了一個DefaultFuture物件並且通過channel.send(req)方法傳送請求到生產者端，這裡不做具體深入了。接著我們跳回DubboInvoker類doInvoke方法中的currentClient.request(inv, timeout).get()，這裡是不是和jdk中future的用法很像，事實上這裡也確實是通過get方法的呼叫將執行緒阻塞在這裡等待結果，從而將非同步呼叫轉化為同步。為了證實這個想法，我們來看看DefaultFuture的get方法
public Object get() throws RemotingException {
return get(timeout);
}
public Object get(int timeout) throws RemotingException {
if (timeout <= 0) {
timeout = Constants.DEFAULT_TIMEOUT;
}
if (! isDone()) {
long start = System.currentTimeMillis();
lock.lock();
try {
while (! isDone()) {
done.await(timeout, TimeUnit.MILLISECONDS);
if (isDone() || System.currentTimeMillis() - start > timeout) {
break;
}
}
} catch (InterruptedException e) {
throw new RuntimeException(e);
} finally {
lock.unlock();
}
if (! isDone()) {
throw new TimeoutException(sent > 0, channel, getTimeoutMessage(false));
}
}
return returnFromResponse();
}
從done.await(timeout, TimeUnit.MILLISECONDS)可以看到這裡不僅是等待isDone()這個狀態位，同時還有超時時間的限制。isDone()判斷的是什麼，來看一下
public boolean isDone() {
return response != null;
}
判斷response物件是否為空，那麼後面的流程其實不難猜，生產者處理完結果會來填充response。
生產者響應呼叫請求
生產者開啟了埠監聽，訊息的解碼由Netty處理，解碼後交由NettyHandler的messageReceived方法進行業務處理，來看一下
public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
NettyChannel channel = NettyChannel.getOrAddChannel(ctx.getChannel(), url, handler);
try {
handler.received(channel, e.getMessage());
} finally {
NettyChannel.removeChannelIfDisconnected(ctx.getChannel());
}
}
先來看一下NettyChannel.getOrAddChannel
static NettyChannel getOrAddChannel(org.jboss.netty.channel.Channel ch, URL url, ChannelHandler handler) {
if (ch == null) {
return null;
}
NettyChannel ret = channelMap.get(ch);
if (ret == null) {
NettyChannel nc = new NettyChannel(ch, url, handler);
if (ch.isConnected()) {
ret = channelMap.putIfAbsent(ch, nc);
}
if (ret == null) {
ret = nc;
}
}
return ret;
}
主要是從channelMap中獲取對應的NettyChannel，接著回到NettyHandler的messageReceived方法來看handler.received(channel, e.getMessage())，這裡的handler是一個NettyServer的例項，但它本身沒有實現received方法，該方法要追溯到它的父類的父類的父類（真的就是這麼長的繼承關係。。。）AbstractPeer中，來看一下
public void received(Channel ch, Object msg) throws RemotingException {
if (closed) {
return;
}
handler.received(ch, msg);
}
這裡的handler是MultiMessageHandler物件的例項，來看一下其received方法的實現
@Override
public void received(Channel channel, Object message) throws RemotingException {
if (message instanceof MultiMessage) {
MultiMessage list = (MultiMessage)message;
for(Object obj : list) {
handler.received(channel, obj);
}
} else {
handler.received(channel, message);
}
}
這裡的handler又是HeartbeatHandler類的例項
public void received(Channel channel, Object message) throws RemotingException {
setReadTimestamp(channel);
if (isHeartbeatRequest(message)) {
Request req = (Request) message;
if (req.isTwoWay()) {
Response res = new Response(req.getId(), req.getVersion());
res.setEvent(Response.HEARTBEAT_EVENT);
channel.send(res);
if (logger.isInfoEnabled()) {
int heartbeat = channel.getUrl().getParameter(Constants.HEARTBEAT_KEY, 0);
if(logger.isDebugEnabled()) {
logger.debug("Received heartbeat from remote channel " + channel.getRemoteAddress()
+ ", cause: The channel has no data-transmission exceeds a heartbeat period"
+ (heartbeat > 0 ? ": " + heartbeat + "ms" : ""));
}
}
}
return;
}
if (isHeartbeatResponse(message)) {
if (logger.isDebugEnabled()) {
logger.debug(
new StringBuilder(32)
.append("Receive heartbeat response in thread ")
.append(Thread.currentThread().getName())
.toString());
}
return;
}
handler.received(channel, message);
}
因為不是心跳類的訊息，所以執行handler.received(channel, message)繼續這個呼叫鏈，這裡的handler是AllChannelHandler型別的
public void received(Channel channel, Object message) throws RemotingException {
ExecutorService cexecutor = getExecutorService();
try {
cexecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.RECEIVED, message));
} catch (Throwable t) {
throw new ExecutionException(message, channel, getClass() + " error when process received event .", t);
}
}
這裡終於結束了呼叫鏈，轉而啟動了一個執行緒池來執行任務，那我們來看看具體的任務執行緒ChannelEventRunnable中到底需要執行什麼任務
public void run() {
switch (state) {
case CONNECTED:
try{
handler.connected(channel);
}catch (Exception e) {
logger.warn("ChannelEventRunnable handle " + state + " operation error, channel is " + channel, e);
}
break;
case DISCONNECTED:
try{
handler.disconnected(channel);
}catch (Exception e) {
logger.warn("ChannelEventRunnable handle " + state + " operation error, channel is " + channel, e);
}
break;
case SENT:
try{
handler.sent(channel,message);
}catch (Exception e) {
logger.warn("ChannelEventRunnable handle " + state + " operation error, channel is " + channel
+ ", message is "+ message,e);
}
break;
case RECEIVED:
try{
handler.received(channel, message);
}catch (Exception e) {
logger.warn("ChannelEventRunnable handle " + state + " operation error, channel is " + channel
+ ", message is "+ message,e);
}
break;
case CAUGHT:
try{
handler.caught(channel, exception);
}catch (Exception e) {
logger.warn("ChannelEventRunnable handle " + state + " operation error, channel is "+ channel
+ ", message is: " + message + ", exception is " + exception,e);
}
break;
default:
logger.warn("unknown state: " + state + ", message is " + message);
}
}
這裡傳入的是RECEIVED狀態，執行對應分支又是呼叫handler.received(channel, message)，好吧繼續。。。
這裡的handler是DecodeHandler的例項，繼續跟下去
public void received(Channel channel, Object message) throws RemotingException {
if (message instanceof Decodeable) {
decode(message);
}
if (message instanceof Request) {
decode(((Request)message).getData());
}
if (message instanceof Response) {
decode( ((Response)message).getResult());
}
handler.received(channel, message);
}
呼叫鏈還在繼續，這次的handler是HeaderExchangeHandler型別
public void received(Channel channel, Object message) throws RemotingException {
channel.setAttribute(KEY_READ_TIMESTAMP, System.currentTimeMillis());
ExchangeChannel exchangeChannel = HeaderExchangeChannel.getOrAddChannel(channel);
try {
if (message instanceof Request) {
// handle request.
Request request = (Request) message;
//判斷是心跳還是正常請求
if (request.isEvent()) {
handlerEvent(channel, request);
} else {
if (request.isTwoWay()) {
Response response = handleRequest(exchangeChannel, request);
channel.send(response);
} else {
handler.received(exchangeChannel, request.getData());
}
}
} else if (message instanceof Response) {
handleResponse(channel, (Response) message);
} else if (message instanceof String) {
if (isClientSide(channel)) {
Exception e = new Exception("Dubbo client can not supported string message: " + message + " in channel: " + channel + ", url: " + channel.getUrl());
logger.error(e.getMessage(), e);
} else {
String echo = handler.telnet(channel, (String) message);
if (echo != null && echo.length() > 0) {
channel.send(echo);
}
}
} else {
handler.received(exchangeChannel, message);
}
} finally {
HeaderExchangeChannel.removeChannelIfDisconnected(channel);
}
}
正常同步請求會開始執行handleRequest(exchangeChannel, request)處理請求，並通過channel.send(response)回覆結果，來重點看一下handleRequest方法
Response handleRequest(ExchangeChannel channel, Request req) throws RemotingException {
Response res = new Response(req.getId(), req.getVersion());
//處理異常的請求
if (req.isBroken()) {
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);
return res;
}
// find handler by message class.
Object msg = req.getData();
try {
// handle data.
Object result = handler.reply(channel, msg);
res.setStatus(Response.OK);
res.setResult(result);
} catch (Throwable e) {
res.setStatus(Response.SERVICE_ERROR);
res.setErrorMessage(StringUtils.toString(e));
}
return res;
}
可以看出正常請求將由handler.reply(channel, msg)處理，這裡的handler是DubboProtocol中的一個ExchangeHandlerAdapter實現，其reply方法如下
public Object reply(ExchangeChannel channel, Object message) throws RemotingException {
if (message instanceof Invocation) {
Invocation inv = (Invocation) message;
//通過方法名獲取Invoker
Invoker<?> invoker = getInvoker(channel, inv);
//如果是callback 需要處理高版本呼叫低版本的問題
if (Boolean.TRUE.toString().equals(inv.getAttachments().get(IS_CALLBACK_SERVICE_INVOKE))){
String methodsStr = invoker.getUrl().getParameters().get("methods");
boolean hasMethod = false;
if (methodsStr == null || methodsStr.indexOf(",") == -1){
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());
return invoker.invoke(inv);
}
throw new RemotingException(channel, "Unsupported request: " + message == null ? null : (message.getClass().getName() + ": " + message) + ", channel: consumer: " + channel.getRemoteAddress() + " --> provider: " + channel.getLocalAddress());
}
這裡一共做了兩件事，先通過getInvoker(channel, inv)獲取具體的invoker，再通過invoker.invoke(inv)執行獲取結果，先來看一下getInvoker(channel, inv)
Invoker<?> getInvoker(Channel channel, Invocation inv) throws RemotingException{
boolean isCallBackServiceInvoke = false;
boolean isStubServiceInvoke = false;
int port = channel.getLocalAddress().getPort();
String path = inv.getAttachments().get(Constants.PATH_KEY);
//如果是客戶端的回撥服務.
isStubServiceInvoke = Boolean.TRUE.toString().equals(inv.getAttachments().get(Constants.STUB_EVENT_KEY));
if (isStubServiceInvoke){
port = channel.getRemoteAddress().getPort();
}
//callback
isCallBackServiceInvoke = isClientSide(channel) && !isStubServiceInvoke;
if(isCallBackServiceInvoke){
path = inv.getAttachments().get(Constants.PATH_KEY)+"."+inv.getAttachments().get(Constants.CALLBACK_SERVICE_KEY);
inv.getAttachments().put(IS_CALLBACK_SERVICE_INVOKE, Boolean.TRUE.toString());
}
String serviceKey = serviceKey(port, path, inv.getAttachments().get(Constants.VERSION_KEY), inv.getAttachments().get(Constants.GROUP_KEY));
DubboExporter<?> exporter = (DubboExporter<?>) exporterMap.get(serviceKey);
if (exporter == null)
throw new RemotingException(channel, "Not found exported service: " + serviceKey + " in " + exporterMap.keySet() + ", may be version or group mismatch " + ", channel: consumer: " + channel.getRemoteAddress() + " --> provider: " + channel.getLocalAddress() + ", message:" + inv);
return exporter.getInvoker();
}
這裡又看到了熟悉的exporterMap，之前講生產者初始化的時候就說過這個map中放入了封裝過的Invoker物件exporter，現在又把它取了出了並通過getInvoker()方法獲得封裝在其中的Invoker物件。
接著來看invoker.invoke(inv)方法，其實現首先在InvokerWrapper類中
public Result invoke(Invocation invocation) throws RpcException {
return invoker.invoke(invocation);
}
然後會呼叫到AbstractProxyInvoker中的invoke方法
public Result invoke(Invocation invocation) throws RpcException {
try {
return new RpcResult(doInvoke(proxy, invocation.getMethodName(), invocation.getParameterTypes(), invocation.getArguments()));
} catch (InvocationTargetException e) {
return new RpcResult(e.getTargetException());
} catch (Throwable e) {
throw new RpcException("Failed to invoke remote proxy method " + invocation.getMethodName() + " to " + getUrl() + ", cause: " + e.getMessage(), e);
}
}
這裡doInvoke方法的實現在JavassistProxyFactory中getInvoker方法中
public <T> Invoker<T> getInvoker(T proxy, Class<T> type, URL url) {
// TODO Wrapper類不能正確處理帶$的類名
final Wrapper wrapper = Wrapper.getWrapper(proxy.getClass().getName().indexOf('$') < 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);
}
};
}
這裡根據傳入的 proxy物件的類資訊建立對它的包裝物件Wrapper
並呼叫其invokeMethod方法，通過傳入的引數來呼叫proxy物件的對應方法，返回呼叫結果，也就是執行具體的業務。
完成handleRequest(exchangeChannel, request)方法的解析後，回到HeaderExchangeHandler類中接著來看一下channel.send(response)，這裡的channel傳入的是NettyChannel型別的物件，send方法的實現在其父類的父類AbstractPeer中，來看一下
public void send(Object message) throws RemotingException {
send(message, url.getParameter(Constants.SENT_KEY, false));
}
其具體實現又在NettyChannel中
public void send(Object message, boolean sent) throws RemotingException {
super.send(message, sent);
boolean success = true;
int timeout = 0;
try {
ChannelFuture future = channel.write(message);
if (sent) {
timeout = getUrl().getPositiveParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT);
success = future.await(timeout);
}
Throwable cause = future.getCause();
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");
}
}
可以看到業務處理結果最後通過ChannelFuture物件進行了傳送，到此生產者端的任務就完成了。
消費者獲取呼叫結果
這裡消費者端通過NETTY從生產者端獲取資料的流程和之前的如出一轍，呼叫鏈直到HeaderExchangeHandler之前都是一樣的，我們先來回顧一下HeaderExchangeHandler的received方法
public void received(Channel channel, Object message) throws RemotingException {
channel.setAttribute(KEY_READ_TIMESTAMP, System.currentTimeMillis());
ExchangeChannel exchangeChannel = HeaderExchangeChannel.getOrAddChannel(channel);
try {
if (message instanceof Request) {
// handle request.
Request request = (Request) message;
//判斷是心跳還是正常請求
if (request.isEvent()) {
handlerEvent(channel, request);
} else {
if (request.isTwoWay()) {
Response response = handleRequest(exchangeChannel, request);
channel.send(response);
} else {
handler.received(exchangeChannel, request.getData());
}
}
} else if (message instanceof Response) {
handleResponse(channel, (Response) message);
} else if (message instanceof String) {
if (isClientSide(channel)) {
Exception e = new Exception("Dubbo client can not supported string message: " + message + " in channel: " + channel + ", url: " + channel.getUrl());
logger.error(e.getMessage(), e);
} else {
String echo = handler.telnet(channel, (String) message);
if (echo != null && echo.length() > 0) {
channel.send(echo);
}
}
} else {
handler.received(exchangeChannel, message);
}
} finally {
HeaderExchangeChannel.removeChannelIfDisconnected(channel);
}
}
之前走的是Request分支，這次因為是響應訊息走的是Response分支，那麼來看一下handleResponse(channel, (Response) message)的具體實現
static void handleResponse(Channel channel, Response response) throws RemotingException {
if (response != null && !response.isHeartbeat()) {
DefaultFuture.received(channel, response);
}
}
繼續跟進去看received方法
public static void received(Channel channel, Response response) {
try {
DefaultFuture future = FUTURES.remove(response.getId());
if (future != null) {
future.doReceived(response);
} else {
logger.warn("The timeout response finally returned at "
+ (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS").format(new Date()))
+ ", response " + response
+ (channel == null ? "" : ", channel: " + channel.getLocalAddress()
+ " -> " + channel.getRemoteAddress()));
}
} finally {
CHANNELS.remove(response.getId());
}
}
繼續看doReceived幹了什麼
private void doReceived(Response res) {
lock.lock();
try {
response = res;
if (done != null) {
done.signal();
}
} finally {
lock.unlock();
}
if (callback != null) {
invokeCallback(callback);
}
}
看到這裡把執行結果賦值給response，正好應證了我們之前的猜想，消費者的同步阻塞也就可以繼續執行下去了，這也算是非常經典的非同步轉同步的實現方案了吧。
總結
本文把消費者端和生產者端互動的大概流程進行了講解，流程主要分為三個部分，分別是：消費者發起呼叫請求、生產者響應呼叫請求和消費者獲取呼叫結果，概括一下就是消費者通過生成的代理物件呼叫invoke方法通過Netty的通道去請求生產者的exporter進行執行，並且通過future的方式將非同步的互動轉為了同步響應。