本篇以Dubbo作为服务端为例.
当配置如下信息时
代码语言：javascript复制<dubbo:application name="infuq-dubbo-provider" />
<dubbo:registry protocol="zookeeper" address="127.0.0.1:2181" check="false" />
<dubbo:protocol name="dubbo" port="20880" threads="200"/>
<dubbo:service ref="queryUserInfoFacade" interface="com.infuq.facade.QueryUserInfoFacade" version="1.0.0" />
<bean id="queryUserInfoFacade" class="com.infuq.facade.impl.QueryUserInfoFacadeImpl" />Spring在启动的过程中,通过DubboNamespaceHandler解析上面的标签.
将每个标签与之对应的BeanDefinition注册到BeanFactory中.
Spring再根据BeanDefinition生成对应的Bean实例.
上面的<dubbo:service />标签最终会生成对应的ServiceBean实例.
代码语言：javascript复制// 源码位置: com.alibaba.dubbo.config.spring.ServiceBean
public class ServiceBean<T> extends ServiceConfig<T> implements InitializingBean, DisposableBean,
ApplicationContextAware, ApplicationListener<ContextRefreshedEvent>, BeanNameAware,
ApplicationEventPublisherAware {
}ServiceBean实现了ApplicationListener<ContextRefreshedEvent>接口.
在Spring创建完所有的Bean之后,最后会发布一个ContextRefreshedEvent事件.
因此ServiceBean的onApplicationEvent()方法会被执行.
代码语言：javascript复制public void onApplicationEvent(ContextRefreshedEvent event) {
if (isDelay() && !isExported() && !isUnexported()) {
if (logger.isInfoEnabled()) {
logger.info("The service ready on spring started. service: " getInterface());
}
// 暴露服务
export();
}
}接下来就进入到了服务暴露的过程.
本篇文章不会详细讲述暴露流程
服务暴露会完成两件事情. 第一件事情是通过Netty开启服务,监听端口.
第二件事情是将服务注册到注册中心.
跟进export()方法, 最后会来到DubboProtocol类.
大体看下它是如何开启服务,监听端口? 留意下,有个属性requestHandler.
代码语言：javascript复制public class DubboProtocol extends AbstractProtocol {
private ExchangeHandler requestHandler = new ExchangeHandlerAdapter() { ... };
private ExchangeServer createServer(URL url) {
// 绑定
server = Exchangers.bind(url, requestHandler);
}
}跟进bind()方法,最后会来到NettyServer的doOpen()方法.
留意下,有个属性nettyServerHandler.
代码语言：javascript复制// 源码位置: com.alibaba.dubbo.remoting.transport.netty4.NettyServer
protected void doOpen() throws Throwable {
bootstrap = new ServerBootstrap();
bossGroup = new NioEventLoopGroup(1, new DefaultThreadFactory("NettyServerBoss", true));
workerGroup = new NioEventLoopGroup(getUrl().getPositiveParameter(Constants.IO_THREADS_KEY, Constants.DEFAULT_IO_THREADS), new DefaultThreadFactory("NettyServerWorker", true));
// 重要的Handler
final NettyServerHandler nettyServerHandler = new NettyServerHandler(getUrl(), this);
channels = nettyServerHandler.getChannels();
bootstrap.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.childOption(ChannelOption.TCP_NODELAY, Boolean.TRUE)
.childOption(ChannelOption.SO_REUSEADDR, Boolean.TRUE)
.childOption(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT)
.childHandler(new ChannelInitializer<NioSocketChannel>() {
@Override
protected void initChannel(NioSocketChannel ch) throws Exception {
NettyCodecAdapter adapter = new NettyCodecAdapter(getCodec(), getUrl(), NettyServer.this);
ch.pipeline()
.addLast("decoder", adapter.getDecoder())
.addLast("encoder", adapter.getEncoder())
.addLast("handler", nettyServerHandler);// 处理请求和响应的Handler
}
});
// bind
ChannelFuture channelFuture = bootstrap.bind(getBindAddress());
channelFuture.syncUninterruptibly();
channel = channelFuture.channel();
}从DubboProtocol类的requestHandler属性到NettyServer的nettyServerHandler属性.
这一路会经历很多Handler,经过层层封装,最后才封装成NettyServerHandler.
它会经历如下Handler
NettyServerHandler -> NettyServer -> MultiMessageHandler -> HeartbeatHandler -> AllChannelHandler -> DecodeHandler -> HeaderExchangeHandler -> ExchangeHandler
当客户端连接服务端,或者发送数据到服务端的时候,
首先会由NettyServerHandler处理请求,然后依次将请求传递下去,最后到ExchangeHandler.
那么这些Handler是否都由同一个线程执行的吗? 并不是
如上图, 在AllChannelHandler中有个executor属性,它是一个线程池.
NettyServerHandler -> NettyServer -> MultiMessageHandler -> HeartbeatHandler -> AllChannelHandler
以上这几个Handler是由同一个线程执行的, 是由Netty的IO线程执行的, 名称类似NettyServerWorker-5-7
-> DecodeHandler -> HeaderExchangeHandler -> ExchangeHandler
以上这几个Handler是由另一类线程执行的, 是由AllChannelHandler中的线程池执行的, 名称类似DubboServerHandler-2.0.1.15:20880-thread-57
也就是说, Netty的IO线程在接收到请求后, 先依次执行
NettyServerHandler -> NettyServer ->
MultiMessageHandler -> HeartbeatHandler
-> AllChannelHandler 这五个Handler.
之后会由AllChannelHandler中的线程池执行后面的DecodeHandler -> HeaderExchangeHandler -> ExchangeHandler 这三个Handler.
<dubbo:protocol name="dubbo" port="20880" threads="200" threadpool="fixed" />使用threads=200, threadpool=fixed 就是在配置图中红色区域的线程池. 线程池也是调优的一个地方.
