Re: Socket switch delay

From: Alexander Nickolov (agnickolov_at_mvps.org)
Date: 08/24/04

  • Next message: Alexander Nickolov: "Re: Socket switch delay" 
    Date: Tue, 24 Aug 2004 13:17:31 -0700

    Your sever side send is never partial - it's overlapped. All your
    buffers are queued and will be later sent. You must preserve
    them until notified (BTW, I didn't see any code of yours to
    deal with the notification - you pass NULL event handle and
    NULL APC...). Or at least that's the behavior with a non-blocking
    socket, not sure about a blocking socket. (And I'm not even
    sure it matters if the socket is blocking or not.) 

    -- 
=====================================
Alexander Nickolov
Microsoft MVP [VC], MCSD
email: agnickolov@mvps.org
MVP VC FAQ: http://www.mvps.org/vcfaq
=====================================
"mil" <mil@discussions.microsoft.com> wrote in message 
news:B70055F9-BDAD-4D2E-990C-EB5AB3AD93B9@microsoft.com...
>
> "Alexander Nickolov" wrote:
>
>>(and I noticed you don't do overlapped receive at the server!)
>
>
> The receive operation in the server is overlapped, first I receive a 
> header
> which describes what is coming (with one recv competion io) and then I 
> setup
> buffers and wait for all the data I should be receiving, through the
> completion IO. If not all the data comes back, I calculate the right 
> offsets
> and wait again for the completion io.
>
> I didn't send you that part of the code because it is too long.
>
>
>>would you set the send buffer size to zero on a non-overlapped
>>socket escapes me...).
>
> So I get better performance(?) Since I am sending all the data at once 
> using
> WSA buffers why do I need to copy them again? Of course I changed that in 
> the
> server (so the user can disable the 0 buffering, maybe I should make it
> optional in the client too).
>
>
>>One glaring error is your client does not check it sent all data in one go
>
>
> Hmm, you are right. I thought when I send data it always sends them all or
> it returns an error. I also thought that only the receive can send partial
> buffers where the send always sends the whole thing or nothing.
>
> I think I got this whole thing wrong.
>
>
>
>>though I have no idea if this is your problem. So when you use a >single 
>>socket, what exactly happens with this code and on which >side?
>
> If the previous assumption of mine, is wrong, then that must be the 
> problem.
> Because when the client sends data while the server also sends data, the
> connection fails and the server socket stays locked for a minute or two.
>
>
>>Finally, I've never mixed overlapped with non-overlapped I/O
>>on the same socket. Could that be your problem?
>
> I didn't mix the two models, only the client is not using Overlapped IO. 
> The
> server is using it for all communication and file writing.
>
>
> The problem must be the fact that I don't "expect" the send command to 
> send
> partial buffers. And I am not taking into account that in both the client 
> and
> the server code. Where for the receive, I "obey" the rules.
>
> So only when I am using a single socket and both client and server are
> sending data, the send-operation does not send all the buffers in one go 
> and
> "asks me" to try again (and my code doesn't handle this condition).
>
> I am not saying that this cannot happen with the current code as well, but
> it seems that it mostly happens when both sides try to talk over the same
> socket.
>
> I will change the code accordingly to take this into account at both 
> sides.
>
> Thanks for pointing out all these "omissions" (to put it kindly) in my 
> code ;)
>
> Now back to the drawing board for me :(   I am going to add the checking 
> for
> the send operations in client and server then try again with a single 
> socket.
>
> mil
>
>
>
  • Next message: Alexander Nickolov: "Re: Socket switch delay"

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