WSAAsyncSelect消息机制

WSAAsyncSelect基于Windows消息机制异步I/O模型,为特定网络事件指定系统通知信息.

Applies to: desktop apps only

The WSAAsyncSelect functionrequests Windows message-based notification of network events for asocket.

Syntax

C++

int WSAAsyncSelect(
  _In_  SOCKET s,
  _In_  HWND hWnd,
  _In_  unsigned int wMsg,
  _In_  long lEvent
);

Parameters

s [in]

A descriptor that identifies the socket for which eventnotification is required.
hWnd [in]

A handle that identifies the window that will receive a messagewhen a network event occurs.
wMsg [in]

A message to be received when a network event occurs.
lEvent [in]

A bitmask that specifies a combination of network events in whichthe application is interested.

Return value

If the WSAAsyncSelect functionsucceeds,
the return value is zero, provided that the application'sdeclaration of interest in the network event set was successful.Otherwise, the value SOCKET_ERROR is returned, and a specific errornumber can be retrieved by calling

Remarks

The lEvent parameter isconstructed by using the bitwise OR operator with any value listedin the following table.

Value	Meaning
FD_READ	Set to receive notification of readiness for reading.
FD_WRITE	Wants to receive notification of readiness for writing.
FD_OOB	Wants to receive notification of the arrival of OOB data.
FD_ACCEPT	Wants to receive notification of incoming connections.
FD_CONNECT	Wants to receive notification of completed connection or multipointjoin operation.
FD_CLOSE	Wants to receive notification of socket closure.
FD_QOS	Wants to receive notification of socket Quality of Service (QoS)changes.
FD_GROUP_QOS	Wants to receive notification of socket group Quality of Service(QoS) changes (reserved for future use with socket groups).Reserved.
FD_ROUTING_INTERFACE_CHANGE	Wants to receive notification of routing interface changes for thespecified destination(s).
FD_ADDRESS_LIST_CHANGE	Wants to receive notification of local address list changes for thesocket protocol family.

(2)参数3-wMsg:为套接口事件设定1Event通知消息通常形式（WM_USER + n）

如 #defineWM_USER_SERVER WM_USER+1

(3)参数2-bWnd指定系统通知消息wMsg的窗口句柄.函数若调用成功,

WSAAsyncSelect返回0;否则返回SOCKET_ERROR,这时可用WSAGetLastError来获取错误码.

事实上,成功发送一次消息,通知机制会暂停工作直到有重新激活消息通知机制到来.才可重新激活事件.

水平触发:FD_READ,FD_OOB和FD_ACCEPT 即重新激活,需要引发消息发送的条件.

边缘触发:FD_QOS,FD_GROUP_QOS等.

同一接口多次调用WSAAsyncSelect函数,只有最后一次生效.

因此:

WSAAsyncSelect(s, m_hWnd, WM_USER_SERVER,FD_READ)，加上

WSAAsyncSelect(s, m_hWnd, WM_USER_SERVER,FD_CLOSE) 并不等于

WSAAsyncSelect(s, m_hWnd, WM_USER_SERVER,FD_READ | FD_CLOSE)

取消套接口上的I/O事件消息通知:、

WSAAsyncSelect(s, hWnd, 0, 0)

在MFC编程环境中，使用该消息处理函数

BEGIN_MESSAGE_MAP(CXXXDlg, CDialog)

//{{AFX_MSG_MAP(CXXXDlg)

........

//}}AFX_MSG_MAP

ON_MESSAGE(WM_USER_SERVER, OnServerMsg)

........

END_MESSAGE_MAP()

处理消息函数声明为:

afx_msg void OnSERVERMsg(WPARAM wparam,LPARAM lParam);

它定义为:

void CXXXDlg::OnServerMsg(WPARAM wParam,LPARAM lParam)

{

SOCKET sock = (SOCKET) wParam;

if(WSAGETSELECTERROR(lParam)){

ErrorProcess();

return;

}

switch(WSAGETSELECTEVENT(lParam)){

case FD_READ:

ReadDate(sock); // 读数据并进行相应处理

break;

case FD_CLOSE:

Finsish(sock); //套接口关闭工作

break;

default;

break;

}

}

其中函数会接受到两个参数wParam 和 lParam。

其中 wParam参数指明网络事件套接口，多个套接口指定同一个用户消息，那么就需要根据wParam判断到底是哪个套接口待处理。

lParam参数包含两信息:底字指定发生网络事件，高字包含可能出现错误带代码。

另外 OnServerMsg函数中出现两个宏定义

#defineWSAGETSELECTERROR(lParam) HIWORD(lParam)

#defineWSAGETSELECTEVENT(lparam) LOWORD(lParam)

一般来讲,当用户收到第一个FD_WRITE用户消息时就可以向套接口写数据，直到碰到WSAEWOULBALOCK错误时才

等待下一次FD_WRITE通知消息。

总结：WSAAsynSelect在MFC中使用流程

（1）、使用#define语句定义套接口网络事件设置用户消息值，一般为WM_USER+N形式。

（2）、调用WSAAsynsSelect函数，为套接口设定"网络事件-用户消息-消息接收窗体"的对应关系。

（3）、在消息接收窗体的代码的消息映射模块中，加入ON_MESSAGE宏，设定用户消息的处理函数。

（4）、编写用户处理函数，该函数应该首先使用WSAGETSELECTERROR宏判断是否有错误发生：

然后根据wParam值了解是哪一个套接口上发生了网络事件从而引起用户消息被发送：最后使用

WSAGETSELECTEVENT宏来了解所发生的网络事件，从而进行相应处理。