Re: [lwip-users] UDP socket thread safe problem - arp proccess error if ARP_QUEUEING 1

[Simon Goldschmidt]

"Darius Babrauskas" <address@hidden> wrote:
> Problem are, that etharp_request  very fast - and it executed before  udp 
> packet  queued.  So queued packet not send, when get arp response. It send
> later, maybe after arp timer, or when receiving other packet.

That bug doesn't exist in 1.4.0. It even doesn't really exist in 1.2.0: the 
actual bug is that the netif driver passes incoming packets into the ARP module 
from its input context instead of getting into tcpip_thread first (this was 
however a bug in the example ethernetif.c, so many people copied it).

> To resolve this problem, posible need use semaphores to protect arp table.

No, the complete stack (all modules including UDP, IP, ARP and others) need to 
be accessed from one thread at a time only. While this is fixed in 1.4.0 by 
letting the tcpip_thread check if input packets need to be passed to ARP (the 
netif driver just calls netif->input(p) for all packets), you can implement 
this in your 1.2.0 driver by calling tcpip_callback() to get the ARP input 
packets into tcpip_thread.

Upgrading to 1.4.0 (or 1.4.1 RC1) is of course the cleaner solution - 1.2.0 is 
really old and includes many other bugs that are fixed by now.


Simon

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