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1 线程模型概念
DUBBO默认底层网络通信采用Netty框架，我们编写一个Netty服务端进行观察
public class NettyServer {
public static void main(String[] args) throws Exception {
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup(8);
try {
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.option(ChannelOption.SO_BACKLOG, 128)
.childOption(ChannelOption.SO_KEEPALIVE, true)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new NettyServerHandler());
}
});
ChannelFuture channelFuture = bootstrap.bind(7777).sync();
System.out.println("服务端准备就绪");
channelFuture.channel().closeFuture().sync();
} catch (Exception ex) {
System.out.println(ex.getMessage());
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}
我们看到两个线程组：bossGroup线程组只有一个线程处理客户端连接请求，连接完成后将完成三次握手的SocketChannel连接分发给workerGroup处理读写请求，这两个线程组被称为IO线程。我们再引出另一个概念：业务线程。
服务生产者接收到请求后，如果处理逻辑可以快速处理完成，并且不会发起新IO请求，那么可以直接放在IO线程处理，减少线程池调度与上下文切换提高效率。
服务生产者接收到请求后，如果处理逻辑非常耗时，或者会发起新IO请求例如查询数据库，那么必须派发到业务线程池处理。DUBBO提供了多种线程模型
<dubbo:protocol name="dubbo" dispatcher="all" />
<dubbo:protocol name="dubbo" dispatcher="direct" />
<dubbo:protocol name="dubbo" dispatcher="message" />
<dubbo:protocol name="dubbo" dispatcher="execution" />
<dubbo:protocol name="dubbo" dispatcher="connection" />
不同线程模型会选择使用IO线程还是业务线程
all
所有消息都派发到业务线程池，包括请求，响应，连接事件，断开事件，心跳
direct
所有消息都不派发到业务线程池，全部在IO线程直接执行
message
只有请求响应消息派发到业务线程池，其它连接断开事件，心跳等消息直接在IO线程执行
execution
只有请求消息派发到业务线程池，响应和其它连接断开事件，心跳等消息直接在IO线程执行
connection
在IO线程上将连接断开事件放入队列，有序逐个执行，其它消息派发到业务线程池
2 线程模型确定时机
在生产者暴露服务时已经确定使用哪一种线程模型，默认模型AllDispatcher。消费者确认原理相同参看connect方法
public class NettyTransporter implements Transporter {
@Override
public Server bind(URL url, ChannelHandler listener) throws RemotingException {
return new NettyServer(url, listener);
}
@Override
public Client connect(URL url, ChannelHandler listener) throws RemotingException {
return new NettyClient(url, listener);
}
}
public class NettyServer extends AbstractServer implements Server {
public NettyServer(URL url, ChannelHandler handler) throws RemotingException {
// 默认线程模型all
// MultiMessageHandler(HeartbeatHandler(AllDispatcherHandler))
super(url, ChannelHandlers.wrap(handler, ExecutorUtil.setThreadName(url, SERVER_THREAD_POOL_NAME)));
}
}
ChannelHandlers.wrap方法获取Dispatcher自适应扩展点
public class ChannelHandlers {
protected ChannelHandler wrapInternal(ChannelHandler handler, URL url) {
// AllDispatcher模型是Dispatcher默认自适应扩展点
return new MultiMessageHandler(new HeartbeatHandler(ExtensionLoader.getExtensionLoader(Dispatcher.class).getAdaptiveExtension().dispatch(handler, url)));
}
}
如果配置指定dispatcher属性，扩展点加载器会从URL获取属性值加载对应线程模型
@SPI(AllDispatcher.NAME)
public interface Dispatcher {
@Adaptive({Constants.DISPATCHER_KEY, "channel.handler"})
ChannelHandler dispatch(ChannelHandler handler, URL url);
}
3 源码分析
3.1 AllDispatcher
public class AllDispatcher implements Dispatcher {
// 线程模型名称
public static final String NAME = "all";
// 具体实现策略
@Override
public ChannelHandler dispatch(ChannelHandler handler, URL url) {
return new AllChannelHandler(handler, url);
}
}
public class AllChannelHandler extends WrappedChannelHandler {
@Override
public void connected(Channel channel) throws RemotingException {
// 连接完成事件交给业务线程池
ExecutorService cexecutor = getExecutorService();
try {
cexecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.CONNECTED));
} catch (Throwable t) {
throw new ExecutionException("connect event", channel, getClass() + " error when process connected event", t);
}
}
@Override
public void disconnected(Channel channel) throws RemotingException {
// 断开连接事件交给业务线程池
ExecutorService cexecutor = getExecutorService();
try {
cexecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.DISCONNECTED));
} catch (Throwable t) {
throw new ExecutionException("disconnect event", channel, getClass() + " error when process disconnected event", t);
}
}
@Override
public void received(Channel channel, Object message) throws RemotingException {
// 请求响应事件交给业务线程池
ExecutorService cexecutor = getExecutorService();
try {
cexecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.RECEIVED, message));
} catch (Throwable t) {
if(message instanceof Request && t instanceof RejectedExecutionException) {
Request request = (Request)message;
if(request.isTwoWay()) {
String msg = "Server side(" + url.getIp() + "," + url.getPort() + ") threadpool is exhausted ,detail msg:" + t.getMessage();
Response response = new Response(request.getId(), request.getVersion());
response.setStatus(Response.SERVER_THREADPOOL_EXHAUSTED_ERROR);
response.setErrorMessage(msg);
channel.send(response);
return;
}
}
throw new ExecutionException(message, channel, getClass() + " error when process received event", t);
}
}
@Override
public void caught(Channel channel, Throwable exception) throws RemotingException {
// 异常事件交给业务线程池
ExecutorService cexecutor = getExecutorService();
try {
cexecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.CAUGHT, exception));
} catch (Throwable t) {
throw new ExecutionException("caught event", channel, getClass() + " error when process caught event", t);
}
}
}
3.2 DirectDispatcher
public class DirectDispatcher implements Dispatcher {
// 线程模型名称
public static final String NAME = "direct";
// 具体实现策略
@Override
public ChannelHandler dispatch(ChannelHandler handler, URL url) {
// 直接返回handler表示所有事件交给IO线程处理
return handler;
}
}
3.3 MessageOnlyDispatcher
public class MessageOnlyDispatcher implements Dispatcher {
// 线程模型名称
public static final String NAME = "message";
// 具体实现策略
@Override
public ChannelHandler dispatch(ChannelHandler handler, URL url) {
return new MessageOnlyChannelHandler(handler, url);
}
}
public class MessageOnlyChannelHandler extends WrappedChannelHandler {
@Override
public void received(Channel channel, Object message) throws RemotingException {
// 请求响应事件交给业务线程池处理
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);
}
}
}
3.4 ExecutionDispatcher
public class ExecutionDispatcher implements Dispatcher {
// 线程模型名称
public static final String NAME = "execution";
// 具体实现策略
@Override
public ChannelHandler dispatch(ChannelHandler handler, URL url) {
return new ExecutionChannelHandler(handler, url);
}
}
public class ExecutionChannelHandler extends WrappedChannelHandler {
@Override
public void received(Channel channel, Object message) throws RemotingException {
// 获取业务线程池
ExecutorService cexecutor = getExecutorService();
// 只把请求类消息交给业务线程池处理
if (message instanceof Request) {
try {
cexecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.RECEIVED, message));
} catch (Throwable t) {
if (t instanceof RejectedExecutionException) {
Request request = (Request) message;
if (request.isTwoWay()) {
String msg = "Server side(" + url.getIp() + "," + url.getPort() + ") thread pool is exhausted, detail msg:" + t.getMessage();
Response response = new Response(request.getId(), request.getVersion());
response.setStatus(Response.SERVER_THREADPOOL_EXHAUSTED_ERROR);
response.setErrorMessage(msg);
channel.send(response);
return;
}
}
throw new ExecutionException(message, channel, getClass() + " error when process received event.", t);
}
} else {
handler.received(channel, message);
}
}
}
3.5 ConnectionOrderedDispatcher
public class ConnectionOrderedDispatcher implements Dispatcher {
// 线程模型名称
public static final String NAME = "connection";
// 具体实现策略
@Override
public ChannelHandler dispatch(ChannelHandler handler, URL url) {
return new ConnectionOrderedChannelHandler(handler, url);
}
}
public class ConnectionOrderedChannelHandler extends WrappedChannelHandler {
protected final ThreadPoolExecutor connectionExecutor;
private final int queuewarninglimit;
public ConnectionOrderedChannelHandler(ChannelHandler handler, URL url) {
super(handler, url);
// 构造函数声明只有一个线程的线程池进行串行化处理
String threadName = url.getParameter(Constants.THREAD_NAME_KEY, Constants.DEFAULT_THREAD_NAME);
connectionExecutor = new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>(url.getPositiveParameter(Constants.CONNECT_QUEUE_CAPACITY, Integer.MAX_VALUE)),
new NamedThreadFactory(threadName, true),
new AbortPolicyWithReport(threadName, url)
);
queuewarninglimit = url.getParameter(Constants.CONNECT_QUEUE_WARNING_SIZE, Constants.DEFAULT_CONNECT_QUEUE_WARNING_SIZE);
}
@Override
public void connected(Channel channel) throws RemotingException {
try {
// 检查线程池队列元素个数
checkQueueLength();
// 连接完成事件交给线程池处理
connectionExecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.CONNECTED));
} catch (Throwable t) {
throw new ExecutionException("connect event", channel, getClass() + " error when process connected event .", t);
}
}
@Override
public void disconnected(Channel channel) throws RemotingException {
try {
// 检查线程池队列元素个数
checkQueueLength();
// 连接断开事件交给线程池处理
connectionExecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.DISCONNECTED));
} catch (Throwable t) {
throw new ExecutionException("disconnected event", channel, getClass() + " error when process disconnected event .", t);
}
}
@Override
public void received(Channel channel, Object message) throws RemotingException {
// 请求响应事件交给业务线程池处理
ExecutorService cexecutor = getExecutorService();
try {
cexecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.RECEIVED, message));
} catch (Throwable t) {
if (message instanceof Request && t instanceof RejectedExecutionException) {
Request request = (Request) message;
if (request.isTwoWay()) {
String msg = "Server side(" + url.getIp() + "," + url.getPort() + ") threadpool is exhausted ,detail msg:" + t.getMessage();
Response response = new Response(request.getId(), request.getVersion());
response.setStatus(Response.SERVER_THREADPOOL_EXHAUSTED_ERROR);
response.setErrorMessage(msg);
channel.send(response);
return;
}
}
throw new ExecutionException(message, channel, getClass() + " error when process received event .", t);
}
}
@Override
public void caught(Channel channel, Throwable exception) throws RemotingException {
// 异常事件交给业务线程池处理
ExecutorService cexecutor = getExecutorService();
try {
cexecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.CAUGHT, exception));
} catch (Throwable t) {
throw new ExecutionException("caught event", channel, getClass() + " error when process caught event .", t);
}
}
// 检查队列大小
private void checkQueueLength() {
if (connectionExecutor.getQueue().size() > queuewarninglimit) {
logger.warn(new IllegalThreadStateException("connectionordered channel handler `queue size: " + connectionExecutor.getQueue().size() + " exceed the warning limit number :" + queuewarninglimit));
}
}
}
4 文章总结
本文分析了DUBBO线程模型源码，可以根据不同业务场景选择不同线程模型。后续文章分析DUBBO线程池策略请继续关注。
欢迎大家关注公众号「JAVA前线」查看更多精彩分享文章，主要包括源码分析、实际应用、架构思维、职场分享、产品思考等等，同时欢迎大家加我微信「java_front」一起交流学习
