Re: [lwip-users] Bug in netconn_alloc?

[Simon Goldschmidt]

"Walter Saegesser" <address@hidden> wrote:
> conn = (struct netconn *)memp_malloc(MEMP_NETCONN);
> ... 
>   sys_mbox_set_invalid(&conn->acceptmbox);
> 
> As far as I see, 'acceptmbox' has not been assigned and thus can hold
> any value - if you are unlucky enough even a valid handle. 

The macro sys_mbox_set_invalid() is (like the name says) supposed to set a 
pointer to an mbox to a known state so that we can later check if that pointer 
is valid (mbox created) or invalid (mbox not created).

E.g. if you defined sys_mbox_t to "void*", then you would

#define sys_mbox_set_invalid(mbox) (*mbox = NULL)

since in that define, mbox would have the type "void**".

It has been changed like that because the previous implementation had the 
limitation that sys_mbox_t and sys_sem_t always had to be pointers: we had no 
way to "invalidate" them when using aggregated OS elements (since assigning a 
value - like NULL - does not work then).

So now you might define sys_mbox_t to "struct your_os_mbox", which has a member 
"bool valid". You could then

#define sys_mbox_set_invalid(mbox) ((mbox)->valid = false)


Simon
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