[lwip-users] how to free udp pcb

[Rahul Gundecha]

Hi all,

I am writing a dns client and is using UDP sockets for the same.

I observed that UDP PCBs are not getting freed up, even after closing the sockets.
In my code,  the sockets are closed by calling lwip_close().

Call sequence here is:
lwip_close -> netconn_delete -> netconn_free

The comments on netconn_free() function says this -
 * Delete a netconn and all its resources.
 * The pcb is NOT freed (since we might not be in the right thread context do this).

If this is the case, then which is the right place to free up the udp pcb?
I tried to explicitly free up udp pcb associated with the socket by adding following code in netconn_delete(); still the problem persists.

if(conn->pcb.udp != NULL) {
udp_remove(conn->pcb.udp);
}

Thanks,
Rahul

[Rahul Gundecha]

Please note that I am using lwip version 1.4.0

Thanks,
Rahul

[Kieran Mansley]

On 6 Jan 2012, at 14:12, Rahul Gundecha wrote:

> In my code, the sockets are closed by calling lwip_close().

lwip_close() should be sufficient if you're using the sockets API. Can you give more details of what shows that the PCBs are not being freed?

Kieran
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[Rahul Gundecha]

I am using stats_display() function (from ./src/include/lwip/stats.h) to display the stats about pcb usage. And I observe that the used udp pcb count go on increasing till the available limit and then I get errors whenever I try to create new udp pcb.

               MEM UDP_PCB
[218.174045] : avail: 8
[218.176040] : used: 8
[218.178007] : max: 8
[218.180016] : err: 2

Here I am puzzled with the comment in the code.

"Call sequence here is:
lwip_close -> netconn_delete -> netconn_free

The comments on netconn_free() function says this -
 * Delete a netconn and all its resources.
 * The pcb is NOT freed (since we might not be in the right thread context do this)."

Thanks,
Rahul

[Rahul Gundecha]

I found the root cause, it was one socket which was not getting freed up.

Thanks,
Rahul

[Simon Goldschmidt]

Rahul Gundecha <rahul.g...@gmail.com> wrote:
> Here I am puzzled with the comment in the code.
>
> "Call sequence here is:
> lwip_close -> netconn_delete -> netconn_free
>
> The comments on netconn_free() function says this -
> * Delete a netconn and all its resources.
> * The pcb is NOT freed (since we might not be in the right thread context
> do this)."

The pcb is freed in 'do_delconn()', not in 'netconn_free()': at that point, it should already be freed.

Simon
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