MFC support for Sockets.

SCS.007@mch.scn.de
Tuesday, December 24, 1996

Environment : VC++ 1.52, Windows 3.11 - Might be applicable to ALL versions   
              of MFC and Windows.

Hi All,

I want to start a discussion on the MFC support for sockets. I have gone thru 
the src code and this is the info I've found.

* Every MFC application has to call AfxSocketInit() b'for it can create       
  socket objects( CAsyncSocket etc). This calls WSAStartUp and also creates a 
  new object of type AFX_SOCKSTATE, the definition of which is given below.

struct AFX_SOCKSTATE		// AUXVARS.H
{
    void (FAR* lpfnSockCleanup)();
    HWND hSocketWindow;
    CMapWordToPtr mapSocketHandle;
    CMapWordToPtr mapDeadSockets;
    CPtrList listSocketNotifications;
}; // It's self explanatory to people who have worked with sockets. My 
comment.

* After this, any call to CAsyncSocket::Create() shows the following sequence 
of func calls.
	Create()
	{
		Socket()
                {
		CAsyncSocket::AttachHandle
			{
			// LookUp Handle in list.
			// If first time, create new window.
			// add socket to map in _afxSocketState
			}
		CAsyncSocket::AsyncSelect()
		    {
			WSAAsyncSelect(...)// Here a window handle has to be  
                        specified which will recv mesgs such as FD_READ,      
                        FD_WRITE...
		    }
		}
	}

What I don't understand is, why is a new Window being created every time an 
application calls AfxSocketInit(). Okay, I agree that everything works fine, 
but why create a new window for every application that wants to use sockets, 
when the same support could have been provided with just one window. I'd 
really appreciate it if someone cleared this up for me. There must be some 
reason why the MFC team did this.

Best Regards,
Chandru.

---

Donald C. Asonye -- donald@menudo.uh.edu
Friday, December 27, 1996

[Mini-digest: 2 responses]

> 
> Environment : VC++ 1.52, Windows 3.11 - Might be applicable to ALL versions   
>               of MFC and Windows.
> 
> Hi All,
> 
> I want to start a discussion on the MFC support for sockets. I have gone thru 
> the src code and this is the info I've found.
> 
> * Every MFC application has to call AfxSocketInit() b'for it can create       
>   socket objects( CAsyncSocket etc). This calls WSAStartUp and also creates a 
>   new object of type AFX_SOCKSTATE, the definition of which is given below.
[source snipped]

> 
> What I don't understand is, why is a new Window being created every time an 
> application calls AfxSocketInit(). Okay, I agree that everything works fine, 
> but why create a new window for every application that wants to use sockets, 
> when the same support could have been provided with just one window. I'd 
> really appreciate it if someone cleared this up for me. There must be some 
> reason why the MFC team did this.

Complexity.  Why make things complicated when it does not have
to be?  It is simpler to have a window per application.
Winsock functions such as WSAAsyncSelect() needs a window to
send messages to.  It is faster and easily managed if the
window that receives the messages is unique for every
application.  If not, then mfc would have to do a lot of other
things.  

One more thing is: who knows how many applications will use a
socket?  There is no way to determine this.  The message
handler would be very complicated and long if it had to handle
messages for every application.  Would you like to have one
single window procedure that handles all messages for all
windows applications, no matter what type of application or 
message it is?

> 
> Best Regards,
> Chandru.
> 

By the way, I think it might be a good idea if you play with
the winsock api first before jumping to mfc socket classes.
That is if you have not done so already.  

Take care,
-- 
Donald
**************************************************
*  Pull me under.                                *
*  Pull me under, I am not afraid -Dream Theater *
**************************************************
Email    :mailto:donald@uh.edu 
Samples  :ftp://ftp.hpc.uh.edu/pub/donald
WWW      :http://www.uh.edu/~dasonye
-----From: WnDBSoft@aol.com

In a message dated 96-12-24 14:46:40 EST, you write:

> What I don't understand is, why is a new Window being created every time an

>  application calls AfxSocketInit(). Okay, I agree that everything works
fine, 
> 
>  but why create a new window for every application that wants to use
sockets, 
> 
>  when the same support could have been provided with just one window. I'd 
>  really appreciate it if someone cleared this up for me. There must be some

>  reason why the MFC team did this.
>  

The hWndSocketNotification is a secret, hidden window the sockets create so
that they can pseudo-receive and pusedo-send Windows messages to and from
themselves and the rest of your application.

This helps keep your program from freezing.

Sincerely,
Brian Hart
WnDBSoft Software International
http://members.aol.com/wndbsoft/

---

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