dubbo同步调用、异步调用和是否返回结果源码分析和实例

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();

      try {
          String hello = future.get(1, TimeUnit.SECONDS);
          System.out.println(hello);
        } catch (InterruptedException e) {
          e.printStackTrace();
        } catch (ExecutionException e) {
          e.printStackTrace();
        } catch (TimeoutException 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");
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