libthrift0.9.0解析（二）之TSimpleServer

TSimpleServer简单实现Tserver，代码如下。

/**
 * Simple singlethreaded server for testing.
 *
 */
public class TSimpleServer extends TServer {

  private static final Logger LOGGER = LoggerFactory.getLogger(TSimpleServer.class.getName());

  private boolean stopped_ = false;

  public TSimpleServer(AbstractServerArgs args) {
    super(args);
  }

  public void serve() {
    stopped_ = false;
    try {
      serverTransport_.listen(); // 开启监听
    } catch (TTransportException ttx) {
      LOGGER.error("Error occurred during listening.", ttx);
      return;
    }

    // Run the preServe event
    if (eventHandler_ != null) {
      eventHandler_.preServe(); // 前处理切入
    }

    setServing(true);

    while (!stopped_) {
      TTransport client = null;
      TProcessor processor = null;
      TTransport inputTransport = null;
      TTransport outputTransport = null;
      TProtocol inputProtocol = null;
      TProtocol outputProtocol = null;
      ServerContext connectionContext = null;
      try {
        client = serverTransport_.accept(); // 获得一个client transport
        if (client != null) { // 以下代码根据获取的client transport层层封装
          processor = processorFactory_.getProcessor(client); // 根据client获取processor
          inputTransport = inputTransportFactory_.getTransport(client); // 根据client获取input transport
          outputTransport = outputTransportFactory_.getTransport(client); // 根据client获取output transport
          inputProtocol = inputProtocolFactory_.getProtocol(inputTransport); // 根据input transport获取input protocol
          outputProtocol = outputProtocolFactory_.getProtocol(outputTransport); // 根据output transport获取output protocol
          if (eventHandler_ != null) {// 处理前切入eventHandler根据input/output protocol生成connectionContext
            connectionContext = eventHandler_.createContext(inputProtocol, outputProtocol);
          }
          while (true) {// 一直循环处理同一个用户的请求，processor.process永远返回true，只有抛出异常时（即用户端主动关闭连接）才会继续接收下一个用户的请求。
            if (eventHandler_ != null) {// 切入eventHandler处理前面生成的connectionContext
              eventHandler_.processContext(connectionContext, inputTransport, outputTransport);
            }
            if(!processor.process(inputProtocol, outputProtocol)) {// 调用processor对input/output protocol进行处理
              break;
            }
          }
        }
      } catch (TTransportException ttx) {
        // Client died, just move on
      } catch (TException tx) {
        if (!stopped_) {
          LOGGER.error("Thrift error occurred during processing of message.", tx);
        }
      } catch (Exception x) {
        if (!stopped_) {
          LOGGER.error("Error occurred during processing of message.", x);
        }
      }

      if (eventHandler_ != null) {
        eventHandler_.deleteContext(connectionContext, inputProtocol, outputProtocol);
      }

      if (inputTransport != null) {
        inputTransport.close();
      }

      if (outputTransport != null) {
        outputTransport.close();
      }

    }
    setServing(false);
  }

  public void stop() {
    stopped_ = true;
    serverTransport_.interrupt();
  }
}

首先，开启监听，然后在处理之前面向切面切入前处理流程 eventHandler_.preServe();最后进入接收处理流程。

处理时关键看第54行processor.process()函数。

TProcessor为一单接口，仅含process方法。其子类thrift不再提供，而是根据用户自定义的thrift IDL文件自动生成。然而thrift提供了一个抽象类TBaseProcessor<I>封装了一些常用的实现，该类实现了TProcessor接口，框架自动生成的Processor都继承了该基类。

TBaseProcessor<I>代码如下：

public abstract class TBaseProcessor<I> implements TProcessor {
  private final I iface; // 真正的处理函数实现
  private final Map<String,ProcessFunction<I, ? extends TBase>> processMap;

  protected TBaseProcessor(I iface, Map<String, ProcessFunction<I, ? extends TBase>> processFunctionMap) {
    this.iface = iface;
    this.processMap = processFunctionMap;
  }

  public Map<String,ProcessFunction<I, ? extends TBase>> getProcessMapView() {
    return Collections.unmodifiableMap(processMap);
  }

  @Override
  public boolean process(TProtocol in, TProtocol out) throws TException {
    TMessage msg = in.readMessageBegin(); // 获取请求信息，主要包含函数名信息。
    ProcessFunction fn = processMap.get(msg.name); // 根据函数名信息获取相应的处理函数。
    if (fn == null) { // 若没有相关的处理函数，写入异常并返回。
      TProtocolUtil.skip(in, TType.STRUCT);
      in.readMessageEnd();
      TApplicationException x = new TApplicationException(TApplicationException.UNKNOWN_METHOD, "Invalid method name: '"+msg.name+"'");
      out.writeMessageBegin(new TMessage(msg.name, TMessageType.EXCEPTION, msg.seqid));
      x.write(out);
      out.writeMessageEnd();
      out.getTransport().flush();
      return true;
    }
    fn.process(msg.seqid, in, out, iface); // 处理请求
    return true;
  }
}

ProcessFunction为一抽象类，其子类也是根据IDL自动生成。与IDL中的函数一一对应，为代理处理器。

TBase为IDL中定义的types的基类。T封装了处理函数的参数信息，其子类也是框架根据IDL自动生成。

public abstract class ProcessFunction<I, T extends TBase> {
  private final String methodName;

  private static final Logger LOGGER = LoggerFactory.getLogger(ProcessFunction.class.getName());

  public ProcessFunction(String methodName) {
    this.methodName = methodName;
  }

  public final void process(int seqid, TProtocol iprot, TProtocol oprot, I iface) throws TException {
    T args = getEmptyArgsInstance(); // 获取一个空的参数封装
    try {
      args.read(iprot); // 从input protol中读取所有参数到args中
    } catch (TProtocolException e) {
      iprot.readMessageEnd();
      TApplicationException x = new TApplicationException(TApplicationException.PROTOCOL_ERROR, e.getMessage());
      oprot.writeMessageBegin(new TMessage(getMethodName(), TMessageType.EXCEPTION, seqid));
      x.write(oprot);
      oprot.writeMessageEnd();
      oprot.getTransport().flush();
      return;
    }
    iprot.readMessageEnd(); // 读取参数完毕
    TBase result = null;

    try {
      result = getResult(iface, args); // 获取处理结果
    } catch(Throwable th) {
      LOGGER.error("Internal error processing " + getMethodName(), th);
      TApplicationException x = new TApplicationException(TApplicationException.INTERNAL_ERROR, 
        "Internal error processing " + getMethodName());
      oprot.writeMessageBegin(new TMessage(getMethodName(), TMessageType.EXCEPTION, seqid));
      x.write(oprot);
      oprot.writeMessageEnd();
      oprot.getTransport().flush();
      return;
    }

    if(!isOneway()) {// true表示单向操作不许要返回信息，即函数为void类型。false表示需要返回值，则启用output protol写入结果。
      oprot.writeMessageBegin(new TMessage(getMethodName(), TMessageType.REPLY, seqid));
      result.write(oprot);
      oprot.writeMessageEnd();
      oprot.getTransport().flush();
    }
  }

  protected abstract boolean isOneway();

  public abstract TBase getResult(I iface, T args) throws TException;

  public abstract T getEmptyArgsInstance();

  public String getMethodName() {
    return methodName;
  }
}

 到此为止，基本了解了libthrift的大致框架。在处理函数中主要是与protocol打交道，protocol又是根据input/output transport生成，而input/output transport又是根据client transport生成。总形成三层结构，底层是client transport由server transport的accept函数获得，中层是input/output transport ，顶层是input/output protocol。然而三层之间并不是完全透明不可见的，典型如oprot.getTransport().flush() 对上层暴露了底层，也无伤大雅。

下节介绍protocol以及transport。