Re: [lwip-users] lwIP malloc fail

[Navcon - Pedro Paulo Santos]

I undestand. So I can (and must) call a tcp_write inside recv callback, but 
it can't have a larger size than the internal buffers or else it will return 
an ERR_MEM. If I got what you said, the technique is to send what you can in 
recv callback to improve latency, and send the rest in the sent callback 
function to improve performance (better than calling it in poll callback, 
right?).

In my wrong code, I tried to send more data than buffers can handle inside 
recv callback function. I made a loop of several tcp_write() inside it and 
wrote nothing at the sent and poll callbacks, the result was that I got 
ERR_MEM error and a large part of the data wasn't send.

Thank you!

Pedro Paulo.


From: "Simon Goldschmidt" <address@hidden>
To: "Navcon - Pedro Paulo Santos" <address@hidden>; "Mailing 
list for lwIP users" <address@hidden>
Sent: Wednesday, April 14, 2010 2:38 AM
Subject: Re: [lwip-users] lwIP malloc fail


"Navcon - Pedro Paulo Santos" wrote:
> The main mistake I did was that I tried to send all the data in the recv
> callback function. As I realized, lwIP received the ACK, but didn't freed
> the memory because it does so in other handler (unknown for me) different
> from recv.

Which memory isn't freed? The pbufs queued for sending/retransmission should 
be freed *before* your receive callback is called, so this shouldn't be a 
problem. However, you can only send as much data as fits into the buffers 
when you are in the recv callback. If you have more data than that, the 
*sent* callback gets called if an ACK is received and you can send more data 
from there.

The HTTP server in CVS contrib has no problems doing it this way.

> The latency can be improve for really small tranfers by sending
> in the recv function, but I would not suggest this.

That's not true, there should be no problems sending from the recv callback 
(i.e. calling tcp_write from that callback).

Simon
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__________ Informação do ESET NOD32 Antivirus, versão da vacina 4628 (20091122) 
__________

A mensagem foi verificada pelo  ESET NOD32 Antivirus.

http://www.eset.com