Re: RE : [lwip-users] local connection failed on loopif, race?

[Tai-hwa Liang]

On Mon, 26 Mar 2007, Fr嶮廨ic BERNON wrote:
> The workaround you have find is "something like" the one I proposed in 
> https://savannah.nongnu.org/bugs/?19157 ("lwip_close problems"). It would be good to add 
> a netconn_close in your code. Follow information for bug #19157 : lwip_close problems, I will 
> propose a patch, like (not yet tested like this) :
>
> err_t
> netconn_close(struct netconn *conn)
> {
>  struct api_msg msg;
>
>  if (conn == NULL) {
>    return ERR_VAL;
>  }
>
>  conn->state = NETCONN_CLOSE;
> again:
>  msg.type = API_MSG_CLOSE;
>  msg.msg.conn = conn;
>  api_msg_post(&msg);
>  if (conn->err == ERR_MEM && conn->sem != SYS_SEM_NULL) {
>    sys_sem_wait(conn->sem);
>    goto again;
>  }
>  if (conn->type==NETCONN_TCP) {
>    if (((sock->conn->pcb.tcp->unacked!=NULL) || (sock->conn->pcb.tcp->unsent!=NULL)) 
> && (sock->conn->err==ERR_OK)) {
>      sys_msleep(1);//I don't like that, but...
>      goto again:
>  }
>  conn->state = NETCONN_NONE;
>  return conn->err;
> }

Hi Fr嶮廨ic,

  With your patch, my testing code never hangs(complete millions of
client/server transactions).  It is interesting to note that with a
"sys_msleep(1)" inside the patch, the performance is much better than the
patch without one.  I guess that's probably because the sys_msleep() gives
another thread a chance to run, which is crucial in my testing case.

  On the other hand, for certain low memory constraint, say, MEM_SIZE=1024,
my test usually crashed into a NULL conn->pcb, which requires another
(conn->pcb.tcp != NULL) workaround:

      if ((conn->pcb.tcp != NULL) && ((conn->pcb.tcp->unacked != NULL) ||
        (conn->pcb.tcp->unsent != NULL)) && (conn->err == ERR_OK)) {
        sys_msleep(1);
        goto again;
      }

  However, this workaround does not solve the hanging problem I've mentioned
about in my first post.  It turns out that raising MEM_SIZE to 2048 is the
only 'solution' at this moment.

> -----Message d'origine-----
> De : address@hidden [mailto:address@hidden De la part de Tai-hwa Liang
> Envoy� : lundi 26 mars 2007 08:28
> � : Mailing list for lwIP users
> Objet : Re: [lwip-users] local connection failed on loopif, race?
>
>
> On Mon, 19 Mar 2007, Tai-hwa Liang wrote:
> > Hi,
> >
> >  Is there anyone having success on using loopif in a multi-threaded
> > application?  The attached is a modified unix/proj/unixsim/simhost.c.
> > Basically it is a self-contained server/client which binds/connects to
> > 127.0.0.2 through loopif.
> >
> >  The problem is that this program failed to run indefinitely and hung
> > after a few client <-> server transactions(lwIP CVS version, with
> > LWIP_HAVE_LOOPIF = 1, running on FreeBSD-CURRENT):
> >
> > freebsd> ./simhost -d
> > Host at 127.0.0.2 mask 255.0.0.0 gateway 127.0.0.1
> > System initialized.
> > TCP/IP initialized.
> > netif_set_ipaddr: netif address being changed
> > netif: IP address of interface API message 0x8065a28
> > cli connecting...
[...]
> > tcp_output: snd_wnd 8096, cwnd 2048, wnd 2048, seg == NULL, ack 6539
> > State: FIN_WAIT_1
> > srv listening return, proceed to accept
> > [...hanging...]
>
>   I managed to workaround this hanging by adding a 1 second delay between
> netconn_write() and netconn_delete():
>
>         /* pseudo code */
>         for (;;) {
>                 srv = netconn_new(NETCONN_TCP)
>                 netconn_connect(srv, srv_addr, srv_port);
>                 netconn_write(srv, buf, len, NETCONN_NOCOPY);
>                 sleep(1);       /* this is vital! */
>                 netconn_delete(srv);
>         }
>
>   In addition to that, the default setting of MEMP_NUM_SYS_TIMEOUT in unixsim still isn't 
> able to cope with the load required in my loopif testing case.  Raising the default value 
> from 3 to 8 plus the aforementioned 1 second delay seems to "resolve" the 
> hanging observed in my case.
>
>   Now the question turns to be: why armed sys_timeout() inside lwIP seems to 
> "lost" when the system is heavily stressed?

--
Thanks,

Tai-hwa Liang