在TCPClient里面用到了Connector，这个是干嘛的

1 想也没用，找找代码

Connector::Connector(EventLoop* loop, const InetAddress& serverAddr)
  : loop_(loop),
    serverAddr_(serverAddr),
    connect_(false),
    state_(kDisconnected),
    retryDelayMs_(kInitRetryDelayMs)
{
  LOG_DEBUG << "ctor[" << this << "]";
}

关键参数是哪个？
还用想，EventLoop。
估计所有的操作都会放到loop里面

2 看看头文件吧

  void start();  // can be called in any thread
  void restart();  // must be called in loop thread
  void stop();  // can be called in any thread

感兴趣的方法有三个，分别如上。
下面分析分析

2.1 start

void Connector::start()
{
  connect_ = true;
  loop_->runInLoop(boost::bind(&Connector::startInLoop, this)); // FIXME: unsafe
}

看看，确实是在loop里面执行的。
代码不全，再贴一点

void Connector::startInLoop()
{
  loop_->assertInLoopThread();
  assert(state_ == kDisconnected);
  if (connect_)
  {
    connect();
  }
  else
  {
    LOG_DEBUG << "do not connect";
  }
}

void Connector::connect()
{
  int sockfd = sockets::createNonblockingOrDie(serverAddr_.family());
  int ret = sockets::connect(sockfd, serverAddr_.getSockAddr());
  int savedErrno = (ret == 0) ? 0 : errno;
  switch (savedErrno)
  {
    case 0:
    case EINPROGRESS:
    case EINTR:
    case EISCONN:
      connecting(sockfd);
      break;

    case EAGAIN:
    case EADDRINUSE:
    case EADDRNOTAVAIL:
    case ECONNREFUSED:
    case ENETUNREACH:
      retry(sockfd);
      break;

    case EACCES:
    case EPERM:
    case EAFNOSUPPORT:
    case EALREADY:
    case EBADF:
    case EFAULT:
    case ENOTSOCK:
      LOG_SYSERR << "connect error in Connector::startInLoop " << savedErrno;
      sockets::close(sockfd);
      break;

    default:
      LOG_SYSERR << "Unexpected error in Connector::startInLoop " << savedErrno;
      sockets::close(sockfd);
      // connectErrorCallback_();
      break;
  }
}

这么多行，我就不看了。
意思就是执行下connect()

2.2 restart

void Connector::restart()
{
  loop_->assertInLoopThread();
  setState(kDisconnected);
  retryDelayMs_ = kInitRetryDelayMs;
  connect_ = true;
  startInLoop();
}

关键代码有两行，
设置断开的状态setState(kDisconnected);
连接startInLoop();
跟start()差不多

2.3 stop

void Connector::stop()
{
  connect_ = false;
  loop_->queueInLoop(boost::bind(&Connector::stopInLoop, this)); // FIXME: unsafe
  // FIXME: cancel timer
}

void Connector::stopInLoop()
{
  loop_->assertInLoopThread();
  if (state_ == kConnecting)
  {
    setState(kDisconnected);
    int sockfd = removeAndResetChannel();
    retry(sockfd);
  }
}

代码少，直接上。

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