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

[Darius Babrauskas]

Maybe in LWIP 1.4v  tcp and udp sockets working ok in  tcpip_thread context.

> > 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.

But how raw api? It must working in  tcpip_thread context?
In LWIP 1.2v  my aplication main task   using  udp_sendto  function, which 
internaly use etharp_output,  which use  etharp_query which using not 
protected ARP table.
So problem leave same.  2 task using  one not protected APR table.

Darius

----- Original Message ----- 
From: "Simon Goldschmidt" <address@hidden>
To: "Mailing list for lwIP users" <address@hidden>
Sent: Friday, March 23, 2012 11:03 AM
Subject: Re: [lwip-users] UDP socket thread safe problem - arp proccess 
error if ARP_QUEUEING 1


> "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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