Re: [lwip-users] question on data consistence in the etharp.c module

[Leon Woestenberg]

John,

the core of lwIP is not designed to be thread-safe. The caller must
make sure that only single thread is in the lwIP core functions at once.

The sysarch and/or socket wrapper provides safety against concurrency
issues, and it should handle this.

I am not involved with the implementation of the socket and sysarch
wrappers,
and am rather clueless myself there.

Can someone who works with the wrapper comment on John's remark?

Regards,

Leon.

----- Original Message ----- 
From: "John Taylor" <address@hidden>
To: <address@hidden>
Sent: Tuesday, January 27, 2004 7:48 AM
Subject: [lwip-users] question on data consistence in the etharp.c module


> I have questions about threading and making calls to the etharp.c
> module.  I have been researching of the code (0.7.0) to port LWIP to a
> new platform.  I am using the unix/tapif code as my example for my
> sys_arch code, starting LWIP, and for implementing my own netif
> interface. Below is run sequence for the simhost.c unix application.
>
> THREAD-CONTEXT: Raw Linux/Unix application thread
> 1) Launch unix application - runs main() in simhost.c.
> 2) In main(): initialize the infrastructure for LWIP (stats, sys, mem,
> etc).
> 3) In main(): create and run Thread-Main.
> 4) In main(): pause forever
>
> THREAD-CONTEXT: Thread-Main
> 5) Run entry-funciton, main_thread(), for Thread-Main
> 6) In main_thread(): Finish initializing LWIP (netif, tpcip, ppp, etc).
> Note: the call to tcpip_init() spawns another thread, Thread-LWIP, which
> is where the LWIP stack 'lives'.
> 7) In main_thread(): Add a network interface - call netif_add()
> 8) In netif_add(): Initialize network interface - call tapif_init()
> 9) In tapif_init(): Initialize low-level device - call low_level_init()
> 10) In low_level_init(): Initialize/Setup the TAPDEV interface.
> 11) In low_level_init(): Create an run Thread-Tapif
> 12) return from low_level_init()
> 13) In tapif_init(): Initialize the etharp module - call etharp_init()
> 14) In tapif_init(): Register a timer for period ARP_TMR_INTERVAL - the
> callback is arp_timer.
> 13) return from tapif_init()
> 14) return from netif_add()
> 15) In main_thread(): initialize network application (httpd, shell,
> tcpecho, etc.)
> 16) In main_thread(): wait forever on a semaphore.  This has the effect
> of processing the ARP_TMR_INTERVAL.  When the time period has expired,
> arp_timer() is called, which then calls etharp_tmr(), then it
> re-registers the timer for ARP_TMR_INTERVAL.
>
> THREAD-CONTEXT: Thread-Tapif
> 17) In tapif_thread: Block on select() until there is packet available.
> Then call tapif_input()
> 18) In tapif_input(): Get and processing incoming packet to determine
> type.  Dependeing on type, call either etharp_ip_input() or
> etharp_arp_input().
> 19) loop back to the blocking select().
>
> According to the above sequence:
> -- etharp_init() and etharp_tmr() are called from Thread-Main.
> -- etharp_ip_input() and etharp_arp_input() are called from Thread-Tapif
> -- etharp_output() is called from Thread-LWIP.
>
>
> Questions:
> 1) Is the above sequence correct or I am miss reading the code?
> 2) Upon examining the etharp.c module, I do not see any mutual exclusion
> locking occurring.  Is this correct?
> 3) If there is multi-thread access to the arp table, is this or bug or I
> am overlooking something?
> 4) LWIP supports multiple network interfaces. But does it support
> multiple Ethernet network interfaces?
>
> TIA
> -john
>
>
> John T. Taylor
> Shift-Right Technologies, LLC.
> 433 Comanche Trl
> Lawrenceville, GA 30044
> Tel: 678-344-3115
> Fax: 770-736-9276
> email: address@hidden
> url: www.shift-right.com
>
>
>
>
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