Non-blocking socket question

  • Thread starter Thread starter Joe Kinsella
  • Start date Start date
J

Joe Kinsella

The following code behaves differently from what I would expect:

socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream,
System.Net.Sockets.ProtocolType.Tcp);
socket.Blocking = false;
socket.Connect(ipe);
isConnected = socket.Poll(30*1000000, SelectMode.SelectWrite);

I would have expected that once I set the socket to non-blocking, the
connect would return immediately and the poll would wait up to 30 seconds
for the connect to succeed.

Instead, what I see is that after 10 or so seconds, the Connect() throws a
SocketException ("A non-blocking socket operation could not be completed
immediately").

Am I misunderstanding the documentation? Help would be appreciated.

Joe
 
Hi,

1. "A non-blocking socket operation could not be completed immediately" is
the WSAEWOULDBLOCK error. It is normal for WSAEWOULDBLOCK to be reported as
the result from calling connect on a non-blocking socket, since some time
must elapse for the connection to be established. For detailed information,
please refer to MSDN on "connect" at:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winsock/win
sock/connect_2.asp

2. In .NET, you can use asynchronous socket calls alternatively. Please
refer to MSDN documentation on Socket.BeginConnect and Socket.EndConnect
methods. I believe the following articles and samples are very helpful:

Using an Asynchronous Client Socket
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/htm
l/cpconusingnon-blockingclientsocket.asp?frame=true

Using an Asynchronous Server Socket
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/htm
l/cpconusingnon-blockingserversocket.asp?frame=true

Please feel free to let me know if you have any problems or concens.

Have a nice day!

Regards,
HuangTM
This posting is provided "AS IS" with no warranties, and confers no rights.
 
This is very helpful. If you don't mind, I do however, have a couple more
questions. I chose not the use the asynchronous calls since it requires a
callback, which adds unneeded complexity to what is otherwise a very simple
problem. If I was writing directly to winsock, I would implement it roughly
as I outlined in my post. I have two concerns with doing this in .Net: 1)
the Connect() call does not return immediately but inexplicably seems to
take several seconds, and 2) I'm concerned about the overhead of relying on
a SocketException being thrown then caught for each socket connection I
make.

If you have advice, it would be appreciated.

Joe
 
2) I'm concerned about the overhead of relying on
a SocketException being thrown then caught for each socket connection I
make.
Click to expand...

How many connections do you intend to establish each second?
 
Hi Joe,

Thanks for your response.

1) the Connect() call does not return immediately but inexplicably seems to
take several seconds

I did some test, it will prompt the exception immediately after issuing the
Connect() call on my side. In addition, I stil recommend you use the
asynchronous socket calls.

I look forward to your feedback.

Have a nice day!

Regards,
HuangTM
This posting is provided "AS IS" with no warranties, and confers no rights.
 
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