gRPC Server 端启动流程

旧城等待， 2022-10-22 04:27 430阅读 0赞

# gRPC Server 端启动流程 #

gRPC Server 启动流程，底层实现以 Netty 为例；

## 核心类 ##

*  `io.grpc.Server`

Server 的定义接口，实现类是 `io.grpc.internal.ServerImpl`，实现了服务、方法与方法处理器的绑定，端口监听，不同类型的 Server 实现的调用，Server 生命周期管理等

*  `io.grpc.BindableService`

由编译器生成的服务抽象类的基础接口，并将实现类绑定到服务器，提供将服务的实现的实例绑定到 Server 的方式

*  `io.grpc.ServerInterceptor`

Server 端的拦截器，在方法调用之前会被调用

*  `io.grpc.HandlerRegistry`

方法处理器注册器，所有的方法注册器会注册在这里，通过服务名和方法名查找

*  `io.grpc.ServerServiceDefinition`

服务定义，包含服务描述信息，方法信息集合

*  `io.grpc.ServerMethodDefinition`

方法定义，包含方法描述信息，方法处理器

## 启动流程 ##

### 启动大致流程 ###

1.  创建 `ServerBuilder`
2.  指定端口
3.  为 `ServerBuilder` 添加方法
    
    1.  构建服务定义
        
        1.  通过生成的代码构建方法定义，将方法与处理器绑定
        2.  将方法处理器添加到方法定义中
        3.  将服务定义添加到服务注册器中
4.  添加拦截器等其他的配置
5.  构建 `Server` 实例
    
    1.  构建 `ServerTransport` 实例
        
        1.  遍历所有监听的地址，创建相应的 `NettyServer`
6.  启动 `Server`
    
    1.  遍历所有的 `NettyServer`，调用 `start` 方法启动
        
        1.  创建相应的 `ServerBootstrap`，绑定监听的地址，可以接受连接
        2.  创建 `NettyServerTransport`，调用 `start` 方法启动 `Transport`
        3.  为 `NettyServerTransport` 创建 `NettyServerHandler`，用于处理请求
7.  保持 `Server` 启动状态，启动完成

### Server 定义 ###

Server server = ServerBuilder.forPort(1234) 
                                 .addService(new HelloServiceImpl()) 
                                 .intercept(new CustomServerInterceptor())
                                 .build();
    server.start();
    server.awaitTermination();

#### 绑定端口 ####

指定了要监听的端口，会根据不同的 `Server` 实现绑定端口

*  io.grpc.ServerBuilder\#forPort

public static ServerBuilder<?> forPort(int port) { 
        return ServerProvider.provider().builderForPort(port);
    }

*  io.grpc.netty.NettyServerProvider\#builderForPort

protected NettyServerBuilder builderForPort(int port) { 
      return NettyServerBuilder.forPort(port);
    }

*  io.grpc.netty.NettyServerBuilder\#NettyServerBuilder(int)

最终会使用指定的端口，创建 `InetSocketAddress` 并将其加入到监听的地址集合中

private NettyServerBuilder(int port) { 
        // 将本地 IP 和端口的地址添加到监听的地址集合中
        this.listenAddresses.add(new InetSocketAddress(port));
    }

#### 绑定服务 ####

将指定的服务实现类添加到方法注册器中

*  io.grpc.internal.AbstractServerImplBuilder\#addService(io.grpc.BindableService)

添加的服务是 `BindableService` 接口的实现类的实例

public final T addService(BindableService bindableService) { 
        return addService(checkNotNull(bindableService, "bindableService").bindService());
    }

*  io.github.helloworlde.HelloServiceGrpc.HelloServiceImplBase\#bindService

这个方法是生成的代码，里面创建了服务定义、并绑定了方法与处理器

public final io.grpc.ServerServiceDefinition bindService() { 
        return io.grpc.ServerServiceDefinition.builder(getServiceDescriptor())
                                              .addMethod(getHowAreYouMethod(), asyncUnaryCall(new MethodHandlers<io.github.helloworlde.HelloMessage, io.github.helloworlde.HelloResponse>(this, METHODID_HOW_ARE_YOU)))
                                              .build();
    }

其中 `addMethod` 会获取方法，为方法绑定处理器，即当前的实现类，并构建方法定义；其中 `getHowAreYouMethod`用于获取方法定义，最终返回包含方法类型、全名、编解码等方法描述信息的实例

*  io.github.helloworlde.HelloServiceGrpc.MethodHandlers\#MethodHandlers

通过方法实现类实例和方法的 ID 构建 `MethodHandlers`实例，这个方法也是生成的，在处理请求时会根据方法的 ID 选择不同的实现类调用相应的方法处理请求

MethodHandlers(HelloServiceImplBase serviceImpl, int methodId) { 
        this.serviceImpl = serviceImpl;
        this.methodId = methodId;
    }
    
    @java.lang.Override
    public void invoke(Req request, io.grpc.stub.StreamObserver<Resp> responseObserver) { 
        switch (methodId) { 
            case METHODID_HOW_ARE_YOU:
                serviceImpl.howAreYou((io.github.helloworlde.HelloMessage) request,
                        (io.grpc.stub.StreamObserver<io.github.helloworlde.HelloResponse>) responseObserver);
                break;
            default:
                throw new AssertionError();
        }
    }

*  io.grpc.stub.ServerCalls\#asyncUnaryCall

会根据构建的 `MethodHandlers` 创建相应类型请求的处理器，并将其加入到服务定义中

public static <ReqT, RespT> ServerCallHandler<ReqT, RespT> asyncUnaryCall(UnaryMethod<ReqT, RespT> method) { 
        return new UnaryServerCallHandler<>(method);
    }

创建的 `UnaryServerCallHandler` 会在服务端 `onHalfClose` 时调用构建的 `UnaryMethod`的`invoke`方法，处理请求

*  io.grpc.ServerServiceDefinition.Builder\#build

遍历服务中的所有的方法，构建服务定义

public ServerServiceDefinition build() {
        ServiceDescriptor serviceDescriptor = this.serviceDescriptor;
        // 如果服务定义为 null，则遍历方法，用服务名和方法集合构建新的服务定义
        if (serviceDescriptor == null) {
            List<MethodDescriptor<?, ?>> methodDescriptors = new ArrayList<>(methods.size());
            for (ServerMethodDefinition<?, ?> serverMethod : methods.values()) {
                methodDescriptors.add(serverMethod.getMethodDescriptor());
            }
            serviceDescriptor = new ServiceDescriptor(serviceName, methodDescriptors);
        }
    
        Map<String, ServerMethodDefinition<?, ?>> tmpMethods = new HashMap<>(methods);
        // 遍历方法定义，校验是否所有的方法都在方法定义中
        for (MethodDescriptor<?, ?> descriptorMethod : serviceDescriptor.getMethods()) {
            ServerMethodDefinition<?, ?> removed = tmpMethods.remove(descriptorMethod.getFullMethodName());
        }
    
        // 根据服务定义和方法定义集合构建服务定义
        return new ServerServiceDefinition(serviceDescriptor, methods);
    }

*  io.grpc.internal.AbstractServerImplBuilder\#addService(io.grpc.ServerServiceDefinition)

将服务定义添加到服务注册器中

public final T addService(ServerServiceDefinition service) { 
        // 将服务添加到处理器中
        registryBuilder.addService(checkNotNull(service, "service"));
        return thisT();
    }

*  io.grpc.internal.InternalHandlerRegistry.Builder\#addService

最终将服务定义添加到注册器的 Map 中，key 是服务的全名，value 是服务定义；  
这样就可以在处理请求时根据请求中的服务和方法名称，在注册器中查找对应的方法的处理器，实现调用

Builder addService(ServerServiceDefinition service) { 
        services.put(service.getServiceDescriptor().getName(), service);
        return this;
    }

#### 绑定拦截器 ####

*  io.grpc.internal.AbstractServerImplBuilder\#intercept

通过 `intercept` 方法，将拦截器添加到拦截器集合中

public final T intercept(ServerInterceptor interceptor) { 
        interceptors.add(checkNotNull(interceptor, "interceptor"));
        return thisT();
    }

#### 构建 Server 实例 ####

*  io.grpc.internal.AbstractServerImplBuilder\#build

在构建器中创建 `Server` 的实例

public final Server build() { 
        return new ServerImpl(this, buildTransportServers(getTracerFactories()), Context.ROOT);
    }

*  io.grpc.netty.NettyServerBuilder\#buildTransportServers

构建 `Server` 的 `Transport`，会为每个监听的地址都构建一个 `NettyServer`

protected List<NettyServer> buildTransportServers(List<? extends ServerStreamTracer.Factory> streamTracerFactories) { 
        assertEventLoopsAndChannelType();
    
        ProtocolNegotiator negotiator = protocolNegotiator;
        if (negotiator == null) { 
            negotiator = sslContext != null ? ProtocolNegotiators.serverTls(sslContext, this.getExecutorPool()) : ProtocolNegotiators.serverPlaintext();
        }
    
        List<NettyServer> transportServers = new ArrayList<>(listenAddresses.size());
        // 为每一个监听的地址构建一个 NettyServer
        for (SocketAddress listenAddress : listenAddresses) { 
            NettyServer transportServer = new NettyServer(listenAddress,
                    channelFactory,
                    channelOptions,
                    childChannelOptions,
                    bossEventLoopGroupPool,
                    workerEventLoopGroupPool,
                    forceHeapBuffer,
                    negotiator,
                    streamTracerFactories,
                    getTransportTracerFactory(),
                    maxConcurrentCallsPerConnection,
                    autoFlowControl,
                    flowControlWindow,
                    maxMessageSize,
                    maxHeaderListSize,
                    keepAliveTimeInNanos,
                    keepAliveTimeoutInNanos,
                    maxConnectionIdleInNanos,
                    maxConnectionAgeInNanos,
                    maxConnectionAgeGraceInNanos,
                    permitKeepAliveWithoutCalls,
                    permitKeepAliveTimeInNanos,
                    getChannelz());
            transportServers.add(transportServer);
        }
        return Collections.unmodifiableList(transportServers);
    }

*  io.grpc.internal.ServerImpl\#ServerImpl

创建 `ServerImpl` 实例

ServerImpl(AbstractServerImplBuilder<?> builder,
               List<? extends InternalServer> transportServers,
               Context rootContext) { 
        this.executorPool = Preconditions.checkNotNull(builder.executorPool, "executorPool");
        this.registry = Preconditions.checkNotNull(builder.registryBuilder.build(), "registryBuilder");
        this.fallbackRegistry = Preconditions.checkNotNull(builder.fallbackRegistry, "fallbackRegistry");
        Preconditions.checkNotNull(transportServers, "transportServers");
        Preconditions.checkArgument(!transportServers.isEmpty(), "no servers provided");
        this.transportServers = new ArrayList<>(transportServers);
        this.logId = InternalLogId.allocate("Server", String.valueOf(getListenSocketsIgnoringLifecycle()));
        // Fork from the passed in context so that it does not propagate cancellation, it only
        // inherits values.
        this.rootContext = Preconditions.checkNotNull(rootContext, "rootContext").fork();
        this.decompressorRegistry = builder.decompressorRegistry;
        this.compressorRegistry = builder.compressorRegistry;
        this.transportFilters = Collections.unmodifiableList(new ArrayList<>(builder.transportFilters));
        this.interceptors = builder.interceptors.toArray(new ServerInterceptor[builder.interceptors.size()]);
        this.handshakeTimeoutMillis = builder.handshakeTimeoutMillis;
        this.binlog = builder.binlog;
        this.channelz = builder.channelz;
        this.serverCallTracer = builder.callTracerFactory.create();
        this.ticker = checkNotNull(builder.ticker, "ticker");
        channelz.addServer(this);
    }

### 启动 Server ###

#### 启动 Server ####

*  io.grpc.internal.ServerImpl\#start

启动 `Server`，会创建服务监听器，遍历所有的监听的地址，并启动相应的 `Transport`，修改启动状态为 true

public ServerImpl start() throws IOException { 
        synchronized (lock) { 
            checkState(!started, "Already started");
            checkState(!shutdown, "Shutting down");
            // Start and wait for any ports to actually be bound.
            // 创建服务监听器实例
            ServerListenerImpl listener = new ServerListenerImpl();
            // 遍历 Server 并启动
            for (InternalServer ts : transportServers) { 
                ts.start(listener);
                activeTransportServers++;
            }
            executor = Preconditions.checkNotNull(executorPool.getObject(), "executor");
            started = true;
            return this;
        }
    }

*  io.grpc.netty.NettyServer\#start

启动 Netty Server，会先创建 `ServerBootstrap`，然后在初始化 `Channel` 时会创建 `NettyServerTransport` 并调用其 start 方法启动，并将需要监听的地址绑定在 `ServerBootstrap` 上

@Override
    public void start(ServerListener serverListener) throws IOException { 
      listener = checkNotNull(serverListener, "serverListener");
    
      // 用于启动 Netty ServerChannel
      ServerBootstrap b = new ServerBootstrap();
      b.group(bossGroup, workerGroup);
    
      b.childHandler(new ChannelInitializer<Channel>() { 
        @Override
        public void initChannel(Channel ch) { 
    
          ChannelPromise channelDone = ch.newPromise();
    
          // 构建基于 Netty 的 ServerTransport
          NettyServerTransport transport = new NettyServerTransport(ch,
                  channelDone,
                  protocolNegotiator,
                  streamTracerFactories,
                  transportTracerFactory.create(),
                  maxStreamsPerConnection,
                  autoFlowControl,
                  flowControlWindow,
                  maxMessageSize,
                  maxHeaderListSize,
                  keepAliveTimeInNanos,
                  keepAliveTimeoutInNanos,
                  maxConnectionIdleInNanos,
                  maxConnectionAgeInNanos,
                  maxConnectionAgeGraceInNanos,
                  permitKeepAliveWithoutCalls,
                  permitKeepAliveTimeInNanos);
          ServerTransportListener transportListener;
          synchronized (NettyServer.this) { 
            // 调用监听器回调，Transport 创建事件
            transportListener = listener.transportCreated(transport);
          }
    
          // 启动监听器
          transport.start(transportListener);
        }
      });
      // 绑定地址，接受连接
      ChannelFuture future = b.bind(address);
    
      channel = future.channel();
      channel.eventLoop().execute(new Runnable() { 
        @Override
        public void run() { 
          listenSocketStats = new ListenSocket(channel);
          channelz.addListenSocket(listenSocketStats);
        }
      });
    }

*  io.grpc.internal.ServerImpl.ServerListenerImpl\#transportCreated

`ServerTransport` 创建事件回调

@Override
    public ServerTransportListener transportCreated(ServerTransport transport) { 
        synchronized (lock) { 
            transports.add(transport);
        }
        // Transport 监听器
        ServerTransportListenerImpl stli = new ServerTransportListenerImpl(transport);
        // 初始化监听器，添加握手超时的取消任务
        stli.init();
        return stli;
    }

*  io.grpc.netty.NettyServerTransport\#start

启动 `NettyServerTransport`，会创建相应的 `NettyServerHandler` 用于处理请求；同时添加监听器

public void start(ServerTransportListener listener) { 
        Preconditions.checkState(this.listener == null, "Handler already registered");
        this.listener = listener;
    
        // Create the Netty handler for the pipeline.
        // 为 pipeline 创建 Netty Handler
        grpcHandler = createHandler(listener, channelUnused);
    
        // Notify when the channel closes.
        // 当 Channel 关闭的时候发送通知
        final class TerminationNotifier implements ChannelFutureListener { 
            boolean done;
    
            @Override
            public void operationComplete(ChannelFuture future) throws Exception { 
                if (!done) { 
                    done = true;
                    notifyTerminated(grpcHandler.connectionError());
                }
            }
        }
    
        // 创建 Handler
        ChannelHandler negotiationHandler = protocolNegotiator.newHandler(grpcHandler);
        ChannelHandler bufferingHandler = new WriteBufferingAndExceptionHandler(negotiationHandler);
    
        // 添加监听器
        ChannelFutureListener terminationNotifier = new TerminationNotifier();
        channelUnused.addListener(terminationNotifier);
        channel.closeFuture().addListener(terminationNotifier);
    
        channel.pipeline().addLast(bufferingHandler);
    }

#### 保持 Server 运行 ####

*  io.grpc.internal.ServerImpl\#awaitTermination()

通过轮询关闭的状态，如果没有关闭，则使锁等待，保持 Server 线程的运行

public void awaitTermination() throws InterruptedException { 
        synchronized (lock) { 
            while (!terminated) { 
                lock.wait();
            }
        }
    }