Re: [lwip-users] crash on a lot of outgoing packets

[Christiaan Simons]

Note: I'm posting this to the lwip-ussers list again,
there were some mail problems earlier...

Kyle Treleaven wrote:

> I have a few questions though.  First, it seems to me that the new
> echo server will only keep a connection open that is constantly
> active.  Is that correct?

Yes, otherwise clients could eat up the server resources
if connections stay open infinitely.

> Second, as far as the transmit goes I've
> noticed two major changes:  1) it blocks on pbuf_free to make
> absolutely sure it gets freed,

Yes, this is to ensure it really gets freed. The return value must be 0.

> and 2) there's a pbuf_ref call on the
> new state chain, es->p.  First, what would cause a pbuf not to free?

The ref count not being 1.

> And I guess my real question is, what is the pbuf_ref doing?

If there are multiple references (pointers) to the pbuf,
and you call pbuf_free, the ref counter is decremented.
A pbuf_free on the last reference may actually perform the
deallocation.

This is explained a bit further in the comments in lwip/src/core/pbuf.c

Actually I "abuse" the pbuf_ref increment to chop pbufs at
the head of the chain.

Regards,

Christiaan Simons

Hardware / Software Engineer
Axon Digital Design

+31 (0)13 511 66 66
+31 (0)13 511 41 51

http://www.axon.tv


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