Re: [lwip-users] The sockets interface, select()

[Matias Mandell]

On 9/20/11 4:24 PM, Kieran Mansley wrote:
> On Mon, 2011-09-19 at 10:31 +0300, Matias Mandell wrote:
>
> > In the end of event_callback() when it has gone thru all tasks waiting
> > for a select() it unprotects&protects and starts over from the
> > beginning. At this point the sock->select_waiting was sometimes zero and
> > the loop crashed.
> >
> >
> > In lwip_select() there are protections when adding/removing from list
> > and increasing/decreasing sock->select_waiting counters but they are not
> > in sync. How good idea is it to pass a local variable to another task,
> > there might be context switching in between? I might have a stack
> > overflow or something going on...
> Without looking at the code I'm not quite sure what the problem is.  Do
> you have a patch to fix it as that would show clearly what you're
> describing.
In short, the lwip_select()-function's local variable
    struct lwip_select_cb select_cb;
is also used within the event_callback()-function.

I do not get a crash if I:
- exit the event_callback()-loop upon "sock->select_waiting==0", see 
attached excerpt.
or
- create static memory for the select_cb:s.


There is not a stack overflow, but I'm not sure how the stack is 
saved/loaded upon context switching. I am also experiencing problems 
opening new sockets after closing old ones, I have not looked at it but 
there seems to be another email discussion about it.


Sincerely, Matias

--
mat!as

sockets.c
Description: Text document