Re: [lwip-users] Slow release time of closed TCP PCBs

[address@hidden]

What you are seeing is that the PCBs are remaining in a wait-state for 
some time. This is to prevent packets from the old (closed) connection 
being possibly accept on a new connection. The port stays known to the 
stack and it can send RST packets when new packets for that port are 
received. However, while these PCBs are not yet freed, they are *not* in 
an active state any more, thus tcp_slowtmr is correct.

I guess you'll have to set MEMP_NUM_TCP_PCB higher so that the timeout 
does not keep all PCBs open...

Simon


Lou Cypher wrote:
> I'm using lwIP 1.3.0, with an http-server like application (using as base the
> raw mode httpd in contrib).
>
> When I have many connections to server, i.e. repetitively reloading a page, I
> quickly run into memory errors; enabling debug, and inspecting MEM TCP_PCB in
> stats, I find that all the TCP PCBs are in use, while all the connections have
> been closed properly -- inspecting them with WireShark.
> It needs some seconds (up to around ten), before the PCBs start being freed, and
> I have again sufficient PCBs for new connections -- I'm #defin-ing
> MEMP_NUM_TCP_PCB to 32
>
> If I enable TCP_DEBUG I see the message "tcp_slowtmr: no active pcbs", even when
>  stats_display() shows 100% of TCP PCBs used.
>
> What affects the time/mode to totally release the PCBs for a new task?
>
> Lou
>
>
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