[lwip-users] Re: Knowing when TCP data has been sent

[Sägesser Walter]

>> 
>> Basically it works, i.e. the semaphore is eventually posted, but 
>> unbearably slow (delay of ca. 200ms for each frame). Without this 
>> callback, using NETCONN_COPY for netconn_write, the throughput is at 
>> least 120 times better. Thus I conclude that I have misused the 
>> callback function for something it is not designed for. On the other 
>> hand I do not find a better way to get a "done" trigger. Is there a 
>> better way or do I have to copy the outgoing data (which would violate 
>> the concept of a non-copy interface)?

>Is it slow because you're sending one packet, and then waiting for the 
>callback?  
>With TCP this could wait for a very long time (as you've
>seen) as it needs the other side to ACK it before it can free the buffer and 
>call the callback.  You could get around this by sending lots of buffers 
>without 
>waiting for the callback, and then freeing each one when its callback is 
>called.

>Kieran

Ok, thanks. This is an issue to be considered. 
In the meantime I have encountered another strange thing which might belong to
the same topic. The piece of SW I'm talking about works as a client in an 
embedded device.
If I delete a netconn after each 'netconn_write', I get out twice as many 
packets as if 
I let the netconn alive. This is independent of a callback and is also contrary 
to what I
would have expected. I thought building up a connection is more time consuming 
than just
writing to an existing one.
So, what happens behind the scenes? Based on your explanation above, I could 
imagine that
a) I'm just killing a connection prematurely, before all the handshaking is done
(this lets the question open, how a callback - if registered - is called at 
all) and thus
b) it's only by accident that I get the corret data at the server on my PC, and 
thus
c) I am not allowed to delete a netconn after a successful 'netconn_write' and 
further
d) a callback is mandatory because it's the only way to know when a netconn can 
be deleted.

Actually I'm afraid of believing my own assumptions because it would all be 
dreadfully bad.
What are the facts?

Walter