[sr-dev] Does shm_free() make the pointer NULL?

[Daniel-Constantin Mierla]

Hello,

On 2/28/12 8:14 PM, Iñaki Baz Castillo wrote:
> Hi, I'm realizing that a doble freeing occurs in regex module when it
> fails to start due to module params errors. But I'm sure it didn't
> occur in Kamailio 1.5. My question is the following:
>
>
>    static int *number;
>    number = shm_malloc(sizeof(int));
>    shm_free(number);
>
> Should now number be NULL? I confirm that it's NOT, so I get a double
> freeing since the function free_shared_memory() is executed twice and
> I check "if (number)" before doing "shm_free(number)".
>
> So is it a change in 3.X? should I write:
>
>    shm_free(number);
>    number = NULL;
>
> ?
the pointer is not set to NULL, it never was, no matter the version and 
name, since ser was started. Not even with system malloc, free does not 
set it to null. One reason is that the pointer is given as parameter by 
value, so the variable holding it cannot be changed. Well, in K, 
shm_free() is a macro (define) and can be coded to set it to null, but 
it is a risk if the parameter is an expression (e.g., computing the 
pointer from: a start of a structure + offset).

To be able and safe to set it to null in a function, the parameter must 
be a pointer to the pointer, like:

   static int *number;
   number = shm_malloc(sizeof(int));
   my_shm_free(&number);


Cheers,
Daniel


> -- 
> Daniel-Constantin Mierla -- http://www.asipto.com
> http://linkedin.com/in/miconda -- http://twitter.com/miconda