Re: [lwip-users] Resource starvation

[address@hidden]

Yoav Nissim wrote:
> I've opened a ticket for this issue on savannah, and have a few
> problematic points left.
Great!
> 1. Could you give some feedback as to how we should process each of the
> PCB queues? (e.g retiring a PCB but leaving it to be cleaned up later
> vs. calling the upper layer with an error such as ERR_ABRT). We're not
> sure what the correct behaviour should be for each of the PCB types/states.
I would have thought the code for this is already present in 
netif_set_ipaddr()? I just would have moved this code to a more generic 
function so that it aborts all PCBs which are using the netif's IP 
address as their local address (only if the address is changed, 
listening PCBs can silently be corrected, I guess). Aborting these PCBs 
leads to ERR_ABRT for the upper levels. PCBs using the ANY address can 
live on.
> 2. I believe this modification has exposed another problem: We get an
> ASSERT when our PPP link is disconnected while packets are being
> actively transferred.
The old PPP code was really broken regarding multithreading. The 
modifications that were necessary include that *none* of the PPP 
functions may be called from any other thread than the tcpip_thread (or 
the main loop for NO_SYS==1). The single exception here is pppInProc(), 
which can be called from another thread if PPP_INPROC_MULTITHREADED==1 
(the reason for this is that it would otherwise be quite unperformant 
since we would call into tcpip_thread for every byte vs. every packet).

I'm sorry the change here hasn't been clear, but this is just how lwIP 
works, and the way it was before, it wasn't really thread-safe.

Simon