一個輕量級分佈式 RPC 框架 — NettyRpc

原創 wx5955e325d6bfb 2018-09-11 04:13

原文出處： 阿凡盧

1、背景

最近在搜索Netty和Zookeeper方面的文章時，看到了這篇文章《輕量級分佈式 RPC 框架》，作者用Zookeeper、Netty和Spring寫了一個輕量級的分佈式RPC框架。花了一些時間看了下他的代碼，寫的乾淨簡單，寫的RPC框架可以算是一個簡易版的dubbo。這個RPC框架雖小，但是麻雀雖小，五臟俱全，有興趣的可以學習一下。

本人在這個簡易版的RPC上添加了如下特性：

  • 服務異步調用的支持，回調函數callback的支持

  • 客戶端使用長連接（在多次調用共享連接）

  • 服務端異步多線程處理RPC請求

項目地址：https://github.com/luxiaoxun/NettyRpc

2、簡介

RPC，即 Remote Procedure Call（遠程過程調用），調用遠程計算機上的服務，就像調用本地服務一樣。RPC可以很好的解耦系統，如WebService就是一種基於Http協議的RPC。

這個RPC整體框架如下：

這個RPC框架使用的一些技術所解決的問題：

服務發佈與訂閱：服務端使用Zookeeper註冊服務地址，客戶端從Zookeeper獲取可用的服務地址。

通信：使用Netty作爲通信框架。

Spring：使用Spring配置服務，加載Bean，掃描註解。

動態代理：客戶端使用代理模式透明化服務調用。

消息編解碼：使用Protostuff序列化和反序列化消息。

3、服務端發佈服務

使用註解標註要發佈的服務

服務註解

1
2
3
4
5
6
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Component
public @interface RpcService {
    Class<?> value();
}

一個服務接口：

1
2
3
4
5
6
public interface HelloService {
 
    String hello(String name);
 
    String hello(Person person);
}

一個服務實現：使用註解標註

1
2
3
4
5
6
7
8
9
10
11
12
13
@RpcService(HelloService.class)
public class HelloServiceImpl implements HelloService {
 
    @Override
    public String hello(String name) {
        return "Hello! " + name;
    }
 
    @Override
    public String hello(Person person) {
        return "Hello! " + person.getFirstName() + " " + person.getLastName();
    }
}

服務在啓動的時候掃描得到所有的服務接口及其實現：

1
2
3
4
5
6
7
8
9
10
@Override
    public void setApplicationContext(ApplicationContext ctx) throws BeansException {
        Map<String, Object> serviceBeanMap = ctx.getBeansWithAnnotation(RpcService.class);
        if (MapUtils.isNotEmpty(serviceBeanMap)) {
            for (Object serviceBean : serviceBeanMap.values()) {
                String interfaceName = serviceBean.getClass().getAnnotation(RpcService.class).value().getName();
                handlerMap.put(interfaceName, serviceBean);
            }
        }
    }

在Zookeeper集羣上註冊服務地址：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
public class ServiceRegistry {
 
    private static final Logger LOGGER = LoggerFactory.getLogger(ServiceRegistry.class);
 
    private CountDownLatch latch = new CountDownLatch(1);
 
    private String registryAddress;
 
    public ServiceRegistry(String registryAddress) {
        this.registryAddress = registryAddress;
    }
 
    public void register(String data) {
        if (data != null) {
            ZooKeeper zk = connectServer();
            if (zk != null) {
                AddRootNode(zk); // Add root node if not exist
                createNode(zk, data);
            }
        }
    }
 
    private ZooKeeper connectServer() {
        ZooKeeper zk = null;
        try {
            zk = new ZooKeeper(registryAddress, Constant.ZK_SESSION_TIMEOUT, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    if (event.getState() == Event.KeeperState.SyncConnected) {
                        latch.countDown();
                    }
                }
            });
            latch.await();
        } catch (IOException e) {
            LOGGER.error("", e);
        }
        catch (InterruptedException ex){
            LOGGER.error("", ex);
        }
        return zk;
    }
 
    private void AddRootNode(ZooKeeper zk){
        try {
            Stat s = zk.exists(Constant.ZK_REGISTRY_PATH, false);
            if (s == null) {
                zk.create(Constant.ZK_REGISTRY_PATH, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            }
        } catch (KeeperException e) {
            LOGGER.error(e.toString());
        } catch (InterruptedException e) {
            LOGGER.error(e.toString());
        }
    }
 
    private void createNode(ZooKeeper zk, String data) {
        try {
            byte[] bytes = data.getBytes();
            String path = zk.create(Constant.ZK_DATA_PATH, bytes, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
            LOGGER.debug("create zookeeper node ({} => {})", path, data);
        } catch (KeeperException e) {
            LOGGER.error("", e);
        }
        catch (InterruptedException ex){
            LOGGER.error("", ex);
        }
    }
}
 
ServiceRegistry

這裏在原文的基礎上加了AddRootNode()判斷服務父節點是否存在，如果不存在則添加一個PERSISTENT的服務父節點，這樣雖然啓動服務時多了點判斷，但是不需要手動命令添加服務父節點了。

關於Zookeeper的使用原理，可以看這裏《ZooKeeper基本原理》。

4、客戶端調用服務

使用代理模式調用服務：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
public class RpcProxy {
 
    private String serverAddress;
    private ServiceDiscovery serviceDiscovery;
 
    public RpcProxy(String serverAddress) {
        this.serverAddress = serverAddress;
    }
 
    public RpcProxy(ServiceDiscovery serviceDiscovery) {
        this.serviceDiscovery = serviceDiscovery;
    }
 
    @SuppressWarnings("unchecked")
    public <T> T create(Class<?> interfaceClass) {
        return (T) Proxy.newProxyInstance(
                interfaceClass.getClassLoader(),
                new Class<?>[]{interfaceClass},
                new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        RpcRequest request = new RpcRequest();
                        request.setRequestId(UUID.randomUUID().toString());
                        request.setClassName(method.getDeclaringClass().getName());
                        request.setMethodName(method.getName());
                        request.setParameterTypes(method.getParameterTypes());
                        request.setParameters(args);
 
                        if (serviceDiscovery != null) {
                            serverAddress = serviceDiscovery.discover();
                        }
                        if(serverAddress != null){
                            String[] array = serverAddress.split(":");
                            String host = array[0];
                            int port = Integer.parseInt(array[1]);
 
                            RpcClient client = new RpcClient(host, port);
                            RpcResponse response = client.send(request);
 
                            if (response.isError()) {
                                throw new RuntimeException("Response error.",new Throwable(response.getError()));
                            } else {
                                return response.getResult();
                            }
                        }
                        else{
                            throw new RuntimeException("No server address found!");
                        }
                    }
                }
        );
    }
}

這裏每次使用代理遠程調用服務，從Zookeeper上獲取可用的服務地址，通過RpcClient send一個Request，等待該Request的Response返回。這裏原文有個比較嚴重的bug，在原文給出的簡單的Test中是很難測出來的，原文使用了obj的wait和notifyAll來等待Response返回，會出現“假死等待”的情況：一個Request發送出去後，在obj.wait()調用之前可能Response就返回了，這時候在channelRead0裏已經拿到了Response並且obj.notifyAll()已經在obj.wait()之前調用了，這時候send後再obj.wait()就出現了假死等待，客戶端就一直等待在這裏。使用CountDownLatch可以解決這個問題。

注意：這裏每次調用的send時候纔去和服務端建立連接，使用的是短連接，這種短連接在高併發時會有連接數問題，也會影響性能。

從Zookeeper上獲取服務地址：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
public class ServiceDiscovery {
 
    private static final Logger LOGGER = LoggerFactory.getLogger(ServiceDiscovery.class);
 
    private CountDownLatch latch = new CountDownLatch(1);
 
    private volatile List<String> dataList = new ArrayList<>();
 
    private String registryAddress;
 
    public ServiceDiscovery(String registryAddress) {
        this.registryAddress = registryAddress;
        ZooKeeper zk = connectServer();
        if (zk != null) {
            watchNode(zk);
        }
    }
 
    public String discover() {
        String data = null;
        int size = dataList.size();
        if (size > 0) {
            if (size == 1) {
                data = dataList.get(0);
                LOGGER.debug("using only data: {}", data);
            } else {
                data = dataList.get(ThreadLocalRandom.current().nextInt(size));
                LOGGER.debug("using random data: {}", data);
            }
        }
        return data;
    }
 
    private ZooKeeper connectServer() {
        ZooKeeper zk = null;
        try {
            zk = new ZooKeeper(registryAddress, Constant.ZK_SESSION_TIMEOUT, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    if (event.getState() == Event.KeeperState.SyncConnected) {
                        latch.countDown();
                    }
                }
            });
            latch.await();
        } catch (IOException | InterruptedException e) {
            LOGGER.error("", e);
        }
        return zk;
    }
 
    private void watchNode(final ZooKeeper zk) {
        try {
            List<String> nodeList = zk.getChildren(Constant.ZK_REGISTRY_PATH, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    if (event.getType() == Event.EventType.NodeChildrenChanged) {
                        watchNode(zk);
                    }
                }
            });
            List<String> dataList = new ArrayList<>();
            for (String node : nodeList) {
                byte[] bytes = zk.getData(Constant.ZK_REGISTRY_PATH + "/" + node, false, null);
                dataList.add(new String(bytes));
            }
            LOGGER.debug("node data: {}", dataList);
            this.dataList = dataList;
        } catch (KeeperException | InterruptedException e) {
            LOGGER.error("", e);
        }
    }
}
 
ServiceDiscovery

每次服務地址節點發生變化，都需要再次watchNode，獲取新的服務地址列表。

5、消息編碼

請求消息：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
public class RpcRequest {
 
    private String requestId;
    private String className;
    private String methodName;
    private Class<?>[] parameterTypes;
    private Object[] parameters;
 
    public String getRequestId() {
        return requestId;
    }
 
    public void setRequestId(String requestId) {
        this.requestId = requestId;
    }
 
    public String getClassName() {
        return className;
    }
 
    public void setClassName(String className) {
        this.className = className;
    }
 
    public String getMethodName() {
        return methodName;
    }
 
    public void setMethodName(String methodName) {
        this.methodName = methodName;
    }
 
    public Class<?>[] getParameterTypes() {
        return parameterTypes;
    }
 
    public void setParameterTypes(Class<?>[] parameterTypes) {
        this.parameterTypes = parameterTypes;
    }
 
    public Object[] getParameters() {
        return parameters;
    }
 
    public void setParameters(Object[] parameters) {
        this.parameters = parameters;
    }
}
 
RpcRequest

響應消息：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
public class RpcResponse {
 
    private String requestId;
    private String error;
    private Object result;
 
    public boolean isError() {
        return error != null;
    }
 
    public String getRequestId() {
        return requestId;
    }
 
    public void setRequestId(String requestId) {
        this.requestId = requestId;
    }
 
    public String getError() {
        return error;
    }
 
    public void setError(String error) {
        this.error = error;
    }
 
    public Object getResult() {
        return result;
    }
 
    public void setResult(Object result) {
        this.result = result;
    }
}
 
RpcResponse

消息序列化和反序列化工具：（基於 Protostuff 實現）

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
public class SerializationUtil {
 
    private static Map<Class<?>, Schema<?>> cachedSchema = new ConcurrentHashMap<>();
 
    private static Objenesis objenesis = new ObjenesisStd(true);
 
    private SerializationUtil() {
    }
 
    @SuppressWarnings("unchecked")
    private static <T> Schema<T> getSchema(Class<T> cls) {
        Schema<T> schema = (Schema<T>) cachedSchema.get(cls);
        if (schema == null) {
            schema = RuntimeSchema.createFrom(cls);
            if (schema != null) {
                cachedSchema.put(cls, schema);
            }
        }
        return schema;
    }
 
    /**
     * 序列化（對象 -> 字節數組）
     */
    @SuppressWarnings("unchecked")
    public static <T> byte[] serialize(T obj) {
        Class<T> cls = (Class<T>) obj.getClass();
        LinkedBuffer buffer = LinkedBuffer.allocate(LinkedBuffer.DEFAULT_BUFFER_SIZE);
        try {
            Schema<T> schema = getSchema(cls);
            return ProtostuffIOUtil.toByteArray(obj, schema, buffer);
        } catch (Exception e) {
            throw new IllegalStateException(e.getMessage(), e);
        } finally {
            buffer.clear();
        }
    }
 
    /**
     * 反序列化（字節數組 -> 對象）
     */
    public static <T> T deserialize(byte[] data, Class<T> cls) {
        try {
            T message = (T) objenesis.newInstance(cls);
            Schema<T> schema = getSchema(cls);
            ProtostuffIOUtil.mergeFrom(data, message, schema);
            return message;
        } catch (Exception e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
    }
}
 
SerializationUtil

由於處理的是TCP消息，本人加了TCP的粘包處理Handler

1
channel.pipeline().addLast(new LengthFieldBasedFrameDecoder(65536,0,4,0,0))

消息編解碼時開始4個字節表示消息的長度，也就是消息編碼的時候，先寫消息的長度，再寫消息。

6、性能改進

1）服務端請求異步處理

Netty本身就是一個高性能的網絡框架，從網絡IO方面來說並沒有太大的問題。

從這個RPC框架本身來說，在原文的基礎上把Server端處理請求的過程改成了多線程異步：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
public void channelRead0(final ChannelHandlerContext ctx,final RpcRequest request) throws Exception {
        RpcServer.submit(new Runnable() {
            @Override
            public void run() {
                LOGGER.debug("Receive request " + request.getRequestId());
                RpcResponse response = new RpcResponse();
                response.setRequestId(request.getRequestId());
                try {
                    Object result = handle(request);
                    response.setResult(result);
                } catch (Throwable t) {
                    response.setError(t.toString());
                    LOGGER.error("RPC Server handle request error",t);
                }
                ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE).addListener(new ChannelFutureListener() {
                    @Override
                    public void operationComplete(ChannelFuture channelFuture) throws Exception {
                        LOGGER.debug("Send response for request " + request.getRequestId());
                    }
                });
            }
        });
    }

Netty 4中的Handler處理在IO線程中，如果Handler處理中有耗時的操作（如數據庫相關），會讓IO線程等待，影響性能。

2）服務端長連接的管理

客戶端保持和服務進行長連接，不需要每次調用服務的時候進行連接，長連接的管理（通過Zookeeper獲取有效的地址）。

通過監聽Zookeeper服務節點值的變化，動態更新客戶端和服務端保持的長連接。這個事情現在放在客戶端在做，客戶端保持了和所有可用服務的長連接，給客戶端和服務端都造成了壓力，需要解耦這個實現。

3）客戶端請求異步處理

客戶端請求異步處理的支持，不需要同步等待：發送一個異步請求，返回Feature，通過Feature的callback機制獲取結果。

1
2
3
IAsyncObjectProxy client = rpcClient.createAsync(HelloService.class);
RPCFuture helloFuture = client.call("hello", Integer.toString(i));
String result = (String) helloFuture.get(3000, TimeUnit.MILLISECONDS);

個人覺得該RPC的待改進項：

編碼序列化的多協議支持。 

項目持續更新中。

項目地址：https://github.com/luxiaoxun/NettyRpc

參考：

  • 輕量級分佈式 RPC 框架：http://my.oschina.net/huangyong/blog/361751

  • 你應該知道的RPC原理：http://www.cnblogs.com/LBSer/p/4853234.html


發表評論
所有評論
還沒有人評論，想成為第一個評論的人麼? 請在上方評論欄輸入並且點擊發布.
相關文章

實現一個基於Netty、Zookeeper的分佈式RPC框架（架構）

zcj12396 2019-01-26 17:39:18