Unexpected value-at for NULL'd pointer with pthreads

Jonathan Wakely jwakely.gcc@gmail.com
Mon Aug 24 15:17:00 GMT 2015


On 24 August 2015 at 15:29, Kyle Harper wrote:
>
> void starting_routine(List *list) {
>   // Starting point a thread will use.
>   Buffer *local_buf_ptr;
>   printf("%d : Thread starting up.  local_buf_ptr is currently %d, ",
> pthread_self(), local_buf_ptr);
>   local_buf_ptr = list->pool[0];
>   printf("and is now %d\n", local_buf_ptr);
>   break_crap(list, &local_buf_ptr);

Here you pass the address of a local variable.

>   pthread_exit(0);
> }
>
>
> void break_crap(List *list, Buffer **buf) {
>   // Emulate the buffer removal.
>   pthread_mutex_lock(&list->lock);
>   printf("%d : checking to see if *buf is null\n", pthread_self());
>   if (*buf == NULL) {

Here you check if that local variable is null.

>     printf("%d : *buf is null so I'm leaving.\n", pthread_self());
>     pthread_mutex_unlock(&list->lock);
>     return;
>   }
>   printf("%d : *buf is not null and has ID=%d and lock_id=%d,
> free()ing and NULL-ing\n", pthread_self(), (*buf)->id,
> (*buf)->lock_id);
>   free(*buf);
>   *buf = NULL;

You are nulling the local variable, not the array element it points to.



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