RE: [lwip-users] Bug in pbuf.c regarding PBUF_POOL

[Pettinato, Jim]

I recall hashing this about previously; again I believe it is required
when the OS does not provide a semaphore mechanism to assure the pbuf
pool does not get corrupted. Whether a multi-threaded or single-threaded
implementation, if the ethif interrupt routine is allocating and moving
received packets using pbufs, there has to be a way to prevent that from
happening in the middle of a critical section of the stack's code. THIS
is why SYS_LIGHTWEIGHT_PROT exists and is needed.

Read the comments in sys.h for more background... And someone correct me
if I'm wrong, but I think this was Adam's original protection scheme and
not something 'some programmer' added.

I am using it and must also vote to retain this code.

- Jim


-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf
Of Peter Graf
Sent: Sunday, November 12, 2006 5:25 AM
To: Mailing list for lwIP users
Subject: Re: [lwip-users] Bug in pbuf.c regarding PBUF_POOL


Leon Woestenberg wrote:

>> Thanks for the detailed post - good to see folks getting to grips 
>> with the stack.  The above seemed to summarise quite nicely and I 
>> agree completely with that.
>>
> I completely agree with you; It's good to see there is interest in the

> lwIP stack from developers that are concerned abouts its correctness.
> 
> The SYS_LIGHTWEIGHT_PROT protection was introduced by one of the 
> developers using the stack to protect *ONLY* between interrupt context

> and single-thread user-space context if I am not mistaken.

I think you are mistaken.

> I am all for removing it, because the locking solution does not scale 
> across different platforms.

I have to use SYS_LIGHTWEIGHT_PROT in a _multithreaded_ environment with
interrupt-triggered device driver. Removing it would render lwIP
unusable for me. I guess it lies in the nature of a simple locking
mechanism to be platform specific, but that makes it "lightweight".

I vote against a removal.

All the best
Peter



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