gRPC Client 启动流程

落日映苍穹つ 2022-10-22 02:59 201阅读 0赞

# gRPC Client 启动流程 #

gRPC 启动初始化的流程，使用 Netty 作为底层的实现

## 初始化 Channel ##

Channel 的初始化通过 `ChannelBuilder` 构建  
这里通过 `forTarget` 设置了要解析的服务名称，会通过 `NameResolver` 解析，转换为具体的地址

ManagedChannel channel = ManagedChannelBuilder.forTarget("grpc-server")
                                                  .usePlaintext()
                                                  .build();

*  构建 ManagedChannel 实例

`io.grpc.internal.AbstractManagedChannelImplBuilder#build`

调用 build 时，会根据 builder 中的属性，创建 `ManagedChannelImpl` 的实例

public ManagedChannel build() { 
        return new ManagedChannelOrphanWrapper(new ManagedChannelImpl(
                this,
                // 构建 Transport 工厂
                buildTransportFactory(),
                new ExponentialBackoffPolicy.Provider(),
                // 线程池
                SharedResourcePool.forResource(GrpcUtil.SHARED_CHANNEL_EXECUTOR),
                // 计时器
                GrpcUtil.STOPWATCH_SUPPLIER,
                // 统计和追踪拦截器
                getEffectiveInterceptors(),
                // 时间提供器
                TimeProvider.SYSTEM_TIME_PROVIDER));
    }

## 初始化 Channel 属性 ##

*  io.grpc.internal.ManagedChannelImpl\#ManagedChannelImpl

为 `ManagedChannel` 设置属性，初始化服务发现，负载均衡，拦截器等并创建真正的 Channel

ManagedChannelImpl(AbstractManagedChannelImplBuilder<?> builder,
            ClientTransportFactory clientTransportFactory,
            BackoffPolicy.Provider backoffPolicyProvider,
            ObjectPool<? extends Executor> balancerRpcExecutorPool,
            Supplier<Stopwatch> stopwatchSupplier,
            List<ClientInterceptor> interceptors,
            final TimeProvider timeProvider)

##### 设置服务名称 #####

this.target = checkNotNull(builder.target, "target");

##### 设置 TransportFactory #####

创建了支持鉴权的代理的 `TransportFactory`，用于支持向服务端发起请求进行鉴权

this.transportFactory = new CallCredentialsApplyingTransportFactory(clientTransportFactory, this.executor);

##### 构建服务发现工厂 #####

this.nameResolverFactory = builder.getNameResolverFactory();

*  io.grpc.internal.AbstractManagedChannelImplBuilder\#getNameResolverFactory

如果没有覆盖服务名称，则使用这个 `nameResolverFactory`，否则使用 `OverrideAuthorityNameResolverFactory`

NameResolver.Factory getNameResolverFactory() { 
            if (authorityOverride == null) { 
                return nameResolverFactory;
            } else { 
                return new OverrideAuthorityNameResolverFactory(nameResolverFactory, authorityOverride);
            }
        }

##### 构建服务发现实例 #####

this.nameResolver = getNameResolver(target, nameResolverFactory, nameResolverArgs);

*  io.grpc.internal.ManagedChannelImpl\#getNameResolver

static NameResolver getNameResolver(String target,
                                        NameResolver.Factory nameResolverFactory,
                                        NameResolver.Args nameResolverArgs) { 
      URI targetUri = null;
      StringBuilder uriSyntaxErrors = new StringBuilder();
      // 解析地址
      targetUri = new URI(target);
    
      // 创建 NameResolver
      if (targetUri != null) { 
        NameResolver resolver = nameResolverFactory.newNameResolver(targetUri, nameResolverArgs);
        if (resolver != null) { 
          return resolver;
        }
      }
    
      // 如果不是 URI 格式，则使用默认的 schema
      if (!URI_PATTERN.matcher(target).matches()) { 
        targetUri = new URI(nameResolverFactory.getDefaultScheme(), "", "/" + target, null);
    
        NameResolver resolver = nameResolverFactory.newNameResolver(targetUri, nameResolverArgs);
        if (resolver != null) { 
          return resolver;
        }
      }
      throw new IllegalArgumentException(String.format("cannot find a NameResolver for %s%s", target, uriSyntaxErrors.length() > 0 ? " (" + uriSyntaxErrors + ")" : ""));
    }

##### 设置是否开启重试 #####

根据是否主动开启了重试和禁止重试的开关决定是否要重试

this.retryEnabled = builder.retryEnabled && !builder.temporarilyDisableRetry;

##### 设置负载均衡 #####

根据负载均衡策略构建 `LoadBalancerFactory`，会从注册器中获取并初始化负载均衡实例

this.loadBalancerFactory = new AutoConfiguredLoadBalancerFactory(builder.defaultLbPolicy);

##### 配置信息 #####

// 配置解析器
    ScParser serviceConfigParser = new ScParser(
            retryEnabled,
            builder.maxRetryAttempts,
            builder.maxHedgedAttempts,
            loadBalancerFactory,
            channelLogger);
    
    // 服务配置拦截器
    serviceConfigInterceptor = new ServiceConfigInterceptor(retryEnabled);
    
    // 如果 builder 有配置，则解析配置
    if (builder.defaultServiceConfig != null) { 
      // 解析配置
      ConfigOrError parsedDefaultServiceConfig = serviceConfigParser.parseServiceConfig(builder.defaultServiceConfig);
      this.defaultServiceConfig = (ManagedChannelServiceConfig) parsedDefaultServiceConfig.getConfig();
      this.lastServiceConfig = this.defaultServiceConfig;
    } else { 
      this.defaultServiceConfig = null;
    }
    
    this.lookUpServiceConfig = builder.lookUpServiceConfig;
    
    // 如果没有开启则使用默认配置
    if (!lookUpServiceConfig) { 
      if (defaultServiceConfig != null) { 
        channelLogger.log(ChannelLogLevel.INFO, "Service config look-up disabled, using default service config");
      }
      handleServiceConfigUpdate();
    }

##### 创建 RealChannel #####

`RealChannel` 用于发起请求

Channel channel = new RealChannel(nameResolver.getServiceAuthority());

*  io.grpc.internal.ManagedChannelImpl.RealChannel\#newCall

public <ReqT, RespT> ClientCall<ReqT, RespT> newCall(MethodDescriptor<ReqT, RespT> method,
                                                         CallOptions callOptions) { 
      return new ClientCallImpl<>(method,
              // 执行的线程池
              getCallExecutor(callOptions),
              // 调用的参数
              callOptions,
              // Transport 提供器
              transportProvider,
              // 如果没有关闭，则获取用于调度的执行器
              terminated ? null : transportFactory.getScheduledExecutorService(),
              // 统计 Channel 调用信息
              channelCallTracer,
              // 是否重试
              retryEnabled)
              .setFullStreamDecompression(fullStreamDecompression)
              .setDecompressorRegistry(decompressorRegistry)
              .setCompressorRegistry(compressorRegistry);
    }

##### 拦截器 #####

// 添加方法拦截器
    channel = ClientInterceptors.intercept(channel, serviceConfigInterceptor);

除此之外，还初始化了一些其他的 Channel 的配置和属性，当构建 Channel 完成后，就可以使用 Channel 构建 Stub，用于发起请求