Re: [lwip-users] Clarification of LWIP and multi threading

[address@hidden]

David Hammerton wrote:
> closing a socket, whilest thread 1 is still using it for send/recv, 
> which causes a problem - as yes, that would be a problem in any socket 
> environment.
I think some socket environments support this. The result would be that 
the send/recv call returns with an error message "socket closed".
> So the send there would be happening on the TCP thread (as a result of 
> the message), is that safe to happen while you are reading on your 
> read/write thread anyway?  It must be, as if your read/write thread 
> does a send() followed immedietly by a recv(), it's going to be the 
> same thing.
No, the send() finishes (data copied into tcp_raw buffers) before it 
returns. The means the netconn's state reaches idle (or 'none' in the 
code) so it's free to acept a recv().
> Ok. A little while ago I had an lwIP app that was written using the 
> BSD socket layer, and this is exactly what I did. I had to modify the 
> select() call to be able to pass in another object (representing a 
> semaphore, really) that could be used to interrupt the select() call. 
> I couldn't see any way of creating a socketpair() like object to 
> interrupt the select() call. There is no built in way to do this with 
> the BSD socket layer in lwIP, correct?
Yeah, that's a point currently missing with the basic select() 
implementation we have. Usually, you would just create a loopback socket 
and trigger it, although that's rather unperformant, too.
> But for the netconn layer, I guess I can do my own thing. Is this 
> (below)the correct way to do it?
Seems so, yes. Although there may be more arguments to your 
netconn_calback() than RECV_PLUS.

Simon