手写一个RPC框架，理解更透彻（附源码）

一、前言

前段时间看到一篇不错的文章《看了这篇你就会手写RPC框架了》，于是便来了兴趣对着实现了一遍，后面觉得还有很多优化的地方便对其进行了改进。

主要改动点如下：

• 除了Java序列化协议，增加了protobuf和kryo序列化协议，配置即用。
• 增加多种负载均衡算法（随机、轮询、加权轮询、平滑加权轮询），配置即用。
• 客户端增加本地服务列表缓存，提高性能。
• 修复高并发情况下，netty导致的内存泄漏问题
• 由原来的每个请求建立一次连接，改为建立TCP长连接，并多次复用。
• 服务端增加线程池提高消息处理能力

二、介绍

RPC，即 Remote Procedure Call（远程过程调用），调用远程计算机上的服务，就像调用本地服务一样。RPC可以很好的解耦系统，如WebService就是一种基于Http协议的RPC。

总的来说，就如下几个步骤：

• 客户端（ServerA）执行远程方法时就调用client stub传递类名、方法名和参数等信息。
• client stub会将参数等信息序列化为二进制流的形式，然后通过Sockect发送给服务端（ServerB）
• 服务端收到数据包后，server stub 需要进行解析反序列化为类名、方法名和参数等信息。
• server stub调用对应的本地方法，并把执行结果返回给客户端

所以一个RPC框架有如下角色：

• 服务消费者远程方法的调用方，即客户端。一个服务既可以是消费者也可以是提供者。
• 服务提供者远程服务的提供方，即服务端。一个服务既可以是消费者也可以是提供者。
• 注册中心保存服务提供者的服务地址等信息，一般由zookeeper、redis等实现。
• 监控运维（可选）监控接口的响应时间、统计请求数量等，及时发现系统问题并发出告警通知。

三、实现

本RPC框架rpc-spring-boot-starter涉及技术栈如下：

• 使用zookeeper作为注册中心
• 使用netty作为通信框架
• 消息编解码：protostuff、kryo、java
• spring
• 使用SPI来根据配置动态选择负载均衡算法等

由于代码过多，这里只讲几处改动点。

3.1动态负载均衡算法

1.编写LoadBalance的实现类

2.自定义注解 @LoadBalanceAno

/**
 * 负载均衡注解
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface LoadBalanceAno {

    String value() default "";
}

/**
 * 轮询算法
 */
@LoadBalanceAno(RpcConstant.BALANCE_ROUND)
public class FullRoundBalance implements LoadBalance {

    private static Logger logger = LoggerFactory.getLogger(FullRoundBalance.class);

    private volatile int index;

    @Override
    public synchronized Service chooseOne(List<Service> services) {
        // 加锁防止多线程情况下，index超出services.size()
        if (index == services.size()) {
            index = 0;
        }
        return services.get(index++);
    }
}

3.新建在resource目录下META-INF/servers文件夹并创建文件 4.RpcConfig增加配置项loadBalance

/**
 * @author 2YSP
 * @date 2020/7/26 15:13
 */
@ConfigurationProperties(prefix = "sp.rpc")
public class RpcConfig {

    /**
     * 服务注册中心地址
     */
    private String registerAddress = "127.0.0.1:2181";

    /**
     * 服务暴露端口
     */
    private Integer serverPort = 9999;
    /**
     * 服务协议
     */
    private String protocol = "java";
    /**
     * 负载均衡算法
     */
    private String loadBalance = "random";
    /**
     * 权重，默认为1
     */
    private Integer weight = 1;

   // 省略getter setter
}

5.在自动配置类RpcAutoConfiguration根据配置选择对应的算法实现类

/**
     * 使用spi匹配符合配置的负载均衡算法
     *
     * @param name
     * @return
     */
    private LoadBalance getLoadBalance(String name) {
        ServiceLoader<LoadBalance> loader = ServiceLoader.load(LoadBalance.class);
        Iterator<LoadBalance> iterator = loader.iterator();
        while (iterator.hasNext()) {
            LoadBalance loadBalance = iterator.next();
            LoadBalanceAno ano = loadBalance.getClass().getAnnotation(LoadBalanceAno.class);
            Assert.notNull(ano, "load balance name can not be empty!");
            if (name.equals(ano.value())) {
                return loadBalance;
            }
        }
        throw new RpcException("invalid load balance config");
    }

 @Bean
    public ClientProxyFactory proxyFactory(@Autowired RpcConfig rpcConfig) {
        ClientProxyFactory clientProxyFactory = new ClientProxyFactory();
        // 设置服务发现着
        clientProxyFactory.setServerDiscovery(new           ZookeeperServerDiscovery(rpcConfig.getRegisterAddress()));

        // 设置支持的协议
        Map<String, MessageProtocol> supportMessageProtocols = buildSupportMessageProtocols();
        clientProxyFactory.setSupportMessageProtocols(supportMessageProtocols);
        // 设置负载均衡算法
        LoadBalance loadBalance = getLoadBalance(rpcConfig.getLoadBalance());
        clientProxyFactory.setLoadBalance(loadBalance);
        // 设置网络层实现
        clientProxyFactory.setNetClient(new NettyNetClient());

        return clientProxyFactory;
    }

3.2本地服务列表缓存

使用Map来缓存数据

/**
 * 服务发现本地缓存
 */
public class ServerDiscoveryCache {
    /**
     * key: serviceName
     */
    private static final Map<String, List<Service>> SERVER_MAP = new ConcurrentHashMap<>();
    /**
     * 客户端注入的远程服务service class
     */
    public static final List<String> SERVICE_CLASS_NAMES = new ArrayList<>();

    public static void put(String serviceName, List<Service> serviceList) {
        SERVER_MAP.put(serviceName, serviceList);
    }

    /**
     * 去除指定的值
     * @param serviceName
     * @param service
     */
    public static void remove(String serviceName, Service service) {
        SERVER_MAP.computeIfPresent(serviceName, (key, value) ->
                value.stream().filter(o -> !o.toString().equals(service.toString())).collect(Collectors.toList())
        );
    }

    public static void removeAll(String serviceName) {
        SERVER_MAP.remove(serviceName);
    }


    public static boolean isEmpty(String serviceName) {
        return SERVER_MAP.get(serviceName) == null || SERVER_MAP.get(serviceName).size() == 0;
    }

    public static List<Service> get(String serviceName) {
        return SERVER_MAP.get(serviceName);
    }
}

ClientProxyFactory，先查本地缓存，缓存没有再查询zookeeper。

/**
     * 根据服务名获取可用的服务地址列表
     * @param serviceName
     * @return
     */
    private List<Service> getServiceList(String serviceName) {
        List<Service> services;
        synchronized (serviceName){
            if (ServerDiscoveryCache.isEmpty(serviceName)) {
                services = serverDiscovery.findServiceList(serviceName);
                if (services == null || services.size() == 0) {
                    throw new RpcException("No provider available!");
                }
                ServerDiscoveryCache.put(serviceName, services);
            } else {
                services = ServerDiscoveryCache.get(serviceName);
            }
        }
        return services;
    }

问题：如果服务端因为宕机或网络问题下线了，缓存却还在就会导致客户端请求已经不可用的服务端，增加请求失败率。解决方案：由于服务端注册的是临时节点，所以如果服务端下线节点会被移除。只要监听zookeeper的子节点，如果新增或删除子节点就直接清空本地缓存即可。

DefaultRpcProcessor

/**
 * Rpc处理者，支持服务启动暴露，自动注入Service
 * @author 2YSP
 * @date 2020/7/26 14:46
 */
public class DefaultRpcProcessor implements ApplicationListener<ContextRefreshedEvent> {



    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        // Spring启动完毕过后会收到一个事件通知
        if (Objects.isNull(event.getApplicationContext().getParent())){
            ApplicationContext context = event.getApplicationContext();
            // 开启服务
            startServer(context);
            // 注入Service
            injectService(context);
        }
    }

    private void injectService(ApplicationContext context) {
        String[] names = context.getBeanDefinitionNames();
        for(String name : names){
            Class<?> clazz = context.getType(name);
            if (Objects.isNull(clazz)){
                continue;
            }

            Field[] declaredFields = clazz.getDeclaredFields();
            for(Field field : declaredFields){
                // 找出标记了InjectService注解的属性
                InjectService injectService = field.getAnnotation(InjectService.class);
                if (injectService == null){
                    continue;
                }

                Class<?> fieldClass = field.getType();
                Object object = context.getBean(name);
                field.setAccessible(true);
                try {
                    field.set(object,clientProxyFactory.getProxy(fieldClass));
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
    // 添加本地服务缓存
                ServerDiscoveryCache.SERVICE_CLASS_NAMES.add(fieldClass.getName());
            }
        }
        // 注册子节点监听
        if (clientProxyFactory.getServerDiscovery() instanceof ZookeeperServerDiscovery){
            ZookeeperServerDiscovery serverDiscovery = (ZookeeperServerDiscovery) clientProxyFactory.getServerDiscovery();
            ZkClient zkClient = serverDiscovery.getZkClient();
            ServerDiscoveryCache.SERVICE_CLASS_NAMES.forEach(name ->{
                String servicePath = RpcConstant.ZK_SERVICE_PATH + RpcConstant.PATH_DELIMITER + name + "/service";
                zkClient.subscribeChildChanges(servicePath, new ZkChildListenerImpl());
            });
            logger.info("subscribe service zk node successfully");
        }

    }

    private void startServer(ApplicationContext context) {
        ...

    }
}

ZkChildListenerImpl

/**
 * 子节点事件监听处理类
 */
public class ZkChildListenerImpl implements IZkChildListener {

    private static Logger logger = LoggerFactory.getLogger(ZkChildListenerImpl.class);

    /**
     * 监听子节点的删除和新增事件
     * @param parentPath /rpc/serviceName/service
     * @param childList
     * @throws Exception
     */
    @Override
    public void handleChildChange(String parentPath, List<String> childList) throws Exception {
        logger.debug("Child change parentPath:[{}] -- childList:[{}]", parentPath, childList);
        // 只要子节点有改动就清空缓存
        String[] arr = parentPath.split("/");
        ServerDiscoveryCache.removeAll(arr[2]);
    }
}

3.3nettyClient支持TCP长连接

这部分的改动最多，先增加新的sendRequest接口。

添加接口实现类NettyNetClient

/**
 * @author 2YSP
 * @date 2020/7/25 20:12
 */
public class NettyNetClient implements NetClient {

    private static Logger logger = LoggerFactory.getLogger(NettyNetClient.class);

    private static ExecutorService threadPool = new ThreadPoolExecutor(4, 10, 200,
            TimeUnit.SECONDS, new LinkedBlockingQueue<>(1000), new ThreadFactoryBuilder()
            .setNameFormat("rpcClient-%d")
            .build());

    private EventLoopGroup loopGroup = new NioEventLoopGroup(4);

    /**
     * 已连接的服务缓存
     * key: 服务地址，格式：ip:port
     */
    public static Map<String, SendHandlerV2> connectedServerNodes = new ConcurrentHashMap<>();

    @Override
    public byte[] sendRequest(byte[] data, Service service) throws InterruptedException {
  ....
        return respData;
    }

    @Override
    public RpcResponse sendRequest(RpcRequest rpcRequest, Service service, MessageProtocol messageProtocol) {

        String address = service.getAddress();
        synchronized (address) {
            if (connectedServerNodes.containsKey(address)) {
                SendHandlerV2 handler = connectedServerNodes.get(address);
                logger.info("使用现有的连接");
                return handler.sendRequest(rpcRequest);
            }

            String[] addrInfo = address.split(":");
            final String serverAddress = addrInfo[0];
            final String serverPort = addrInfo[1];
            final SendHandlerV2 handler = new SendHandlerV2(messageProtocol, address);
            threadPool.submit(() -> {
                        // 配置客户端
                        Bootstrap b = new Bootstrap();
                        b.group(loopGroup).channel(NioSocketChannel.class)
                                .option(ChannelOption.TCP_NODELAY, true)
                                .handler(new ChannelInitializer<SocketChannel>() {
                                    @Override
                                    protected void initChannel(SocketChannel socketChannel) throws Exception {
                                        ChannelPipeline pipeline = socketChannel.pipeline();
                                        pipeline
                                                .addLast(handler);
                                    }
                                });
                        // 启用客户端连接
                        ChannelFuture channelFuture = b.connect(serverAddress, Integer.parseInt(serverPort));
                        channelFuture.addListener(new ChannelFutureListener() {
                            @Override
                            public void operationComplete(ChannelFuture channelFuture) throws Exception {
                                connectedServerNodes.put(address, handler);
                            }
                        });
                    }
            );
            logger.info("使用新的连接。。。");
            return handler.sendRequest(rpcRequest);
        }
    }
}

每次请求都会调用sendRequest()方法，用线程池异步和服务端创建TCP长连接，连接成功后将SendHandlerV2缓存到ConcurrentHashMap中方便复用，后续请求的请求地址（ip+port）如果在connectedServerNodes中存在则使用connectedServerNodes中的handler处理不再重新建立连接。

SendHandlerV2

/**
 * @author 2YSP
 * @date 2020/8/19 20:06
 */
public class SendHandlerV2 extends ChannelInboundHandlerAdapter {

    private static Logger logger = LoggerFactory.getLogger(SendHandlerV2.class);

    /**
     * 等待通道建立最大时间
     */
    static final int CHANNEL_WAIT_TIME = 4;
    /**
     * 等待响应最大时间
     */
    static final int RESPONSE_WAIT_TIME = 8;

    private volatile Channel channel;

    private String remoteAddress;

    private static Map<String, RpcFuture<RpcResponse>> requestMap = new ConcurrentHashMap<>();

    private MessageProtocol messageProtocol;

    private CountDownLatch latch = new CountDownLatch(1);

    public SendHandlerV2(MessageProtocol messageProtocol,String remoteAddress) {
        this.messageProtocol = messageProtocol;
        this.remoteAddress = remoteAddress;
    }

    @Override
    public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
        this.channel = ctx.channel();
        latch.countDown();
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        logger.debug("Connect to server successfully:{}", ctx);
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        logger.debug("Client reads message:{}", msg);
        ByteBuf byteBuf = (ByteBuf) msg;
        byte[] resp = new byte[byteBuf.readableBytes()];
        byteBuf.readBytes(resp);
        // 手动回收
        ReferenceCountUtil.release(byteBuf);
        RpcResponse response = messageProtocol.unmarshallingResponse(resp);
        RpcFuture<RpcResponse> future = requestMap.get(response.getRequestId());
        future.setResponse(response);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        logger.error("Exception occurred:{}", cause.getMessage());
        ctx.close();
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ctx.flush();
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        super.channelInactive(ctx);
        logger.error("channel inactive with remoteAddress:[{}]",remoteAddress);
        NettyNetClient.connectedServerNodes.remove(remoteAddress);

    }

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
        super.userEventTriggered(ctx, evt);
    }

    public RpcResponse sendRequest(RpcRequest request) {
        RpcResponse response;
        RpcFuture<RpcResponse> future = new RpcFuture<>();
        requestMap.put(request.getRequestId(), future);
        try {
            byte[] data = messageProtocol.marshallingRequest(request);
            ByteBuf reqBuf = Unpooled.buffer(data.length);
            reqBuf.writeBytes(data);
            if (latch.await(CHANNEL_WAIT_TIME,TimeUnit.SECONDS)){
                channel.writeAndFlush(reqBuf);
                // 等待响应
                response = future.get(RESPONSE_WAIT_TIME, TimeUnit.SECONDS);
            }else {
                throw new RpcException("establish channel time out");
            }
        } catch (Exception e) {
            throw new RpcException(e.getMessage());
        } finally {
            requestMap.remove(request.getRequestId());
        }
        return response;
    }
}

RpcFuture

package cn.sp.rpc.client.net;

import java.util.concurrent.*;

/**
 * @author 2YSP
 * @date 2020/8/19 22:31
 */
public class RpcFuture<T> implements Future<T> {

    private T response;
    /**
     * 因为请求和响应是一一对应的，所以这里是1
     */
    private CountDownLatch countDownLatch = new CountDownLatch(1);
    /**
     * Future的请求时间，用于计算Future是否超时
     */
    private long beginTime = System.currentTimeMillis();

    @Override
    public boolean cancel(boolean mayInterruptIfRunning) {
        return false;
    }

    @Override
    public boolean isCancelled() {
        return false;
    }

    @Override
    public boolean isDone() {
        if (response != null) {
            return true;
        }
        return false;
    }

    /**
     * 获取响应，直到有结果才返回
     * @return
     * @throws InterruptedException
     * @throws ExecutionException
     */
    @Override
    public T get() throws InterruptedException, ExecutionException {
        countDownLatch.await();
        return response;
    }

    @Override
    public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
        if (countDownLatch.await(timeout,unit)){
            return response;
        }
        return null;
    }

    public void setResponse(T response) {
        this.response = response;
        countDownLatch.countDown();
    }

    public long getBeginTime() {
        return beginTime;
    }
}

此处逻辑，第一次执行 SendHandlerV2#sendRequest() 时channel需要等待通道建立好之后才能发送请求，所以用CountDownLatch来控制，等待通道建立。

自定义Future+requestMap缓存来实现netty的请求和阻塞等待响应，RpcRequest对象在创建时会生成一个请求的唯一标识requestId，发送请求前先将RpcFuture缓存到requestMap中，key为requestId，读取到服务端的响应信息后(channelRead方法)，将响应结果放入对应的RpcFuture中。

SendHandlerV2#channelInactive() 方法中，如果连接的服务端异常断开连接了，则及时清理缓存中对应的serverNode。

四、压力测试

测试环境：

• (英特尔)Intel(R) Core(TM) i5-6300HQ CPU @ 2.30GHz 4核
• windows10家庭版（64位）
• 16G内存

1.本地启动zookeeper

2.本地启动一个消费者，两个服务端，轮询算法

3.使用ab进行压力测试，4个线程发送10000个请求

ab -c 4 -n 10000 http://localhost:8080/test/user?id=1

测试结果： 从图片可以看出，10000个请求只用了11s，比之前的130+秒耗时减少了10倍以上。

代码地址：

• https://github.com/2YSP/rpc-spring-boot-starter
• https://github.com/2YSP/rpc-example

本文由哈喽比特于3年以前收录，如有侵权请联系我们。
文章来源：https://mp.weixin.qq.com/s/fc_1aaM2pfZLPnkoH_5h9g