TransportClientFactory

TransportClientFactory是创建传输客户端（TransportClient）的工厂类， TransportClient用于向Netty服务端发送RPC请求，

1.1、由TransportContext创建

  /**
   * Initializes a ClientFactory which runs the given TransportClientBootstraps prior to returning
   * a new Client. Bootstraps will be executed synchronously, and must run successfully in order
   * to create a Client.
   */
  public TransportClientFactory createClientFactory(List bootstraps) {
    return new TransportClientFactory(this, bootstraps);
  }

  public TransportClientFactory createClientFactory() {
    return createClientFactory(Lists.newArrayList());
  }

1.2、组成

• context：即参数传递的TransportContext的引用；
  • conf：即TransportConf，这里通过调用TransportContext的getConf获取；
  • numConnectionsPerPeer：即从TransportConf获取的key为”spark.+模块名+.io.numConnectionsPerPeer”的属性值。此属性值用于指定对等节点间的连接数。这里的模块名实际为TransportConf的module字段，Spark的很多组件都利用RPC框架构建，它们之间按照模块名区分，例如RPC模块的key为“spark.rpc.io.numConnectionsPerPeer”；
  • ioMode：IO模式，即从TransportConf获取key为”spark.+模块名+.io.mode”的属性值。默认值为NIO，Spark还支持EPOLL；
• clientBootstraps：即参数传递的TransportClientBootstrap列表；
• connectionPool：即针对每个Socket地址的连接池ClientPool的缓存；connectionPool的数据结构较为复杂，下图为connectionPool的数据结构。
  • SocketAddress
  • ClientPool
    • clients TransportClient[]
    • locks Object[]
• rand：对Socket地址对应的连接池ClientPool中缓存的TransportClient进行随机选择，对每个连接做负载均衡；
• socketChannelClass：客户端Channel被创建时使用的类，通过ioMode来匹配，默认为NioSocketChannel，Spark还支持EpollEventLoopGroup；
• workerGroup：根据Netty的规范，客户端只有worker组，所以此处创建workerGroup。workerGroup的实际类型是NioEventLoopGroup；
• pooledAllocator ：汇集ByteBuf但对本地线程缓存禁用的分配器。
  • NettyUtils 上面三个都是通过NettyUntils创建

    public TransportClientFactory(
            TransportContext context,
            List clientBootstraps) {
        this.context = Preconditions.checkNotNull(context);
        this.conf = context.getConf();
        this.clientBootstraps = Lists.newArrayList(Preconditions.checkNotNull(clientBootstraps));
        this.connectionPool = new ConcurrentHashMap();
        this.numConnectionsPerPeer = conf.numConnectionsPerPeer();
        this.rand = new Random();

        IOMode ioMode = IOMode.valueOf(conf.ioMode());
        this.socketChannelClass = NettyUtils.getClientChannelClass(ioMode);
        this.workerGroup = NettyUtils.createEventLoop(
                ioMode,
                conf.clientThreads(),
                conf.getModuleName() + "-client");
        this.pooledAllocator = NettyUtils.createPooledByteBufAllocator(
                conf.preferDirectBufs(), false /* allowCache */, conf.clientThreads());
    }