Using WSAsyncsockets

Jonas Almfeldt -- jonal@kuai.se
Tuesday, January 28, 1997

Environment: Win95, VC++ 4.2b

I have a question about connecting a WSAsync socket.
I keep getting the winsock error "WSA Would block" all the time when I try
to connect my socket to an IRC server. How ever this works just fine when I
use the old socket type instead of the WSAsync socket class.

My question is: how do I make a successful socket connection with a WSAsync
socket ?

I am using MSVC++ 4.2 Enterprise Edition under Windows 95.

/ Jonas Almfeldt

---

SCS.010@mch.scn.de
Thursday, January 30, 1997

[Mini-digest: 2 responses]


Hi,

The whole thing has to do with blocking and nonblocking use of sockets. In 
blocking use of sockets any function call will return only after the whole 
operation is completed. In nonblocking use of sockets the call will return 
immediately irrespective of successfull completion of call or not. The 
successfull completion of call is notified by a window message (in 
CAsyncSocket, you have to override a notification function). e.g. let us see 
the use of connect function. The connect function might take some time before 
the connection is actually established with the remote PC (maybe a few 
seconds). In blocking use of sockets this connect call will only return after 
the connection is actually established. In nonblocking use of sockets the 
connect call returns immediately irrespective of whether the connection is 
actually made or not. If the connection is established TRUE is returned, 
otherwise FALSE is returned. In case the connection will take some time to 
establish, FALSE is returned and GetLastError() will give the error code 
"WSAEWOULDBLOCK" and as soon as the connection is established the OnConnect 
function will be called. The same is true will all other socket functions 
like read, write etc..

So in your case you have to override the notification function OnConnect and 
it will be called as soon as the connection is complete.

You can enable blocking or nonblocking mode by calling the function 
AsyncSelect. If you use CAsyncSocket the default mode is nonblocking.

You can see the usefullness of nonblocking use of sockets if you do some 
socket programming for Windows 3.1, which is not a preemptive multitasking 
system and a blocking socket call can block the whole PC for some time. Also 
nonblocking use of sockets is a wonderfull way to provide support for 
multiple simultaneous connections without using threads (again the only way 
in Windows 3.1).

Hope it helps,

Tarun Mehta.


-----From: Mario Contestabile

>My question is: how do I make a successful socket connection with a WSAsync
>socket ?

You may wish to check 
http://www.microsoft.com/msdn/sdk/platforms/doc/sdk/win32/sock/src/wsapiref_4.htm

where it states:

"On a blocking socket, the return value indicates success or failure of the 
connection attempt. 

With a nonblocking socket, the connection attempt cannot be completed 
immediately. In this case, 
connect will return SOCKET_ERROR, and WSAGetLastError will return 
WSAEWOULDBLOCK. In this
 case, there are three different steps you can take: 

1. Use the select function to determine the completion of the connection 
request by checking to see if 
the socket is writeable. 

2. If the application is using WSAAsyncSelect to indicate interest in 
connection events, then the application 
will receive an FD_CONNECT notification indicating that the connect operation 
is complete. 

3. If the application is using WSAEventSelect to indicate interest in 
connection events, then the associated 
event object will be signaled indicating that the connect operation is 
complete. 

Until the connection attempt completes on a nonblocking socket, all subsequent 
calls to connect on the same
socket will fail with the error code WSAEALREADY." 


mcontest@universal.com

---

| Вернуться в корень Архива |