class CAsyncSocketExHelperWindow;
class CAsyncSocketExLayer;
class CCriticalSectionWrapper;

class CAsyncSocketEx : public CObject
{
 DECLARE_DYNAMIC(CAsyncSocketEx)
public:

 //Attaches a new layer to the socket.
 BOOL AddLayer(CAsyncSocketExLayer *pLayer);

 //Trigers an event on the socket
 // Any combination of FD_READ, FD_WRITE, FD_CLOSE, FD_ACCEPT, FD_CONNECT and FD_FORCEREAD is valid for lEvent.
 BOO

. Network Implementation Analysis

    FileZilla的网络部分的结构图如下:

其中CAsyncSocketEx是对MFC的CAsyncSocket的改进，据说比CAysncSocket性能上要高一点。在CAsyncSocketEx中添加了对CAsyncSocketLayer的支持，各个SocketLayer 链接成一个双向的链表（见CAsyncSocketExLayer::m_pNextLayer和CAsyncSocketExLayer::m_pPrevLayer），在CAsyncSocketEx中记录了这个链表的头尾指针。
    对FileZilla来说网络就是其核心，而FillaZilla的网络部分主要就是C