标签：current result remoting 服务 send ddr pcr iss trace
0. dubbo同步调用、异步调用和是否返回结果配置
（1）dubbo默认为同步调用，并且有返回结果。
（2）dubbo异步调用配置，设置 async="true"，异步调用可以提高效率。
（3）dubbo默认是有返回结果，不需要返回，可以设置return="false"，不需要返回值，可以减少等待结果时间。
1. 源码分析（dubbo版本：2.6.0）
dubbo自身底层调用是使用netty异步实现的，默认同步调用返回结果，是通过获取ResponseFuture，然后使用ReentrantLock的await使当前线程等待结果，设置返回的。下面是部分核心代码部分：
com.alibaba.dubbo.rpc.protocol.dubbo.DubboInvoker.doInvoke(Invocation)
@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; if (clients.length == 1) { currentClient = clients[0]; } else { currentClient = clients[index.getAndIncrement() % clients.length]; } try { // 获取是否异步配置async boolean isAsync = RpcUtils.isAsync(getUrl(), invocation); // 获取是否需要返回结果配置return boolean isOneway = RpcUtils.isOneway(getUrl(), invocation); // 获取超时配置timeout int timeout = getUrl().getMethodParameter(methodName, Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT); if (isOneway) { // 不管是否异步，只要不需要返回结果，直接异步调用，设置结果为null boolean isSent = getUrl().getMethodParameter(methodName, Constants.SENT_KEY, false); currentClient.send(inv, isSent); RpcContext.getContext().setFuture(null); return new RpcResult(); } else if (isAsync) { // 如果异步，并且需要返回结果，调用后设置结果future ResponseFuture future = currentClient.request(inv, timeout); RpcContext.getContext().setFuture(new FutureAdapter<Object>(future)); return new RpcResult(); } else { // 如果同步，并且需要返回结果，调用后在此等待，直到有结果设置结果，或者超时抛出异常。 RpcContext.getContext().setFuture(null); 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); } }
2. 实例
这里使用dubbo源码自带的例子
（1）在dubbo-demo-api中定义异步服务
package com.alibaba.dubbo.demo; public interface AsyncDemoService { String sayHello(String name); }
（2）在dubbo-demo-provider中实现
package com.alibaba.dubbo.demo.provider; import java.text.SimpleDateFormat; import java.util.Date; import com.alibaba.dubbo.demo.AsyncDemoService; import com.alibaba.dubbo.rpc.RpcContext; public class AsyncDemoServiceImpl implements AsyncDemoService{ @Override public String sayHello(String name) { System.out.println("[" + new SimpleDateFormat("HH:mm:ss").format(new Date()) + "] Hello " + name + ", request from consumer: " + RpcContext.getContext().getRemoteAddress()); return "Hello " + name + ", response form provider: " + RpcContext.getContext().getLocalAddress(); } }
（3）在dubbo-demo-provider.xml中配置服务信息
<bean id="asyncDemoService" class="com.alibaba.dubbo.demo.provider.AsyncDemoServiceImpl"/> <dubbo:service interface="com.alibaba.dubbo.demo.AsyncDemoService" ref="asyncDemoService"/>
（4）在dubbo-demo-consumer.xml中配置调用服务信息，设置为异步调用async="true"
<dubbo:reference id="asyncDemoService" check="false" interface="com.alibaba.dubbo.demo.AsyncDemoService">
<dubbo:method name="sayHello" async="true"/>
</dubbo:reference>
（5）在dubbo-demo-consumer的Consumer类中增加调用
AsyncDemoService asyncDemoService = (AsyncDemoService) context.getBean("asyncDemoService");
asyncDemoService.sayHello("world");
// 通过 1.源码分析 中可以知道异步返回结果放到了RpcContext.getContext()中
Future<String> future = RpcContext.getContext().getFuture();
while(!future.isDone()){
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
try {
System.out.println(future.get());
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
（6）不需要返回结果，配置dubbo-demo-consumer.xml 中return="false"，同步异步的调用方式一样的，很简单，只需要调用一下就可以继续其他操作，下面是异步的例子。
AsyncDemoService asyncDemoService = (AsyncDemoService) context.getBean("asyncDemoService");
asyncDemoService.sayHello("world");
标签：current result remoting 服务 send ddr pcr iss trace
原文地址：https://www.cnblogs.com/xkzhangsanx/p/11256043.html
