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

[Lou Cypher]

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