Lock-free queue

Question

Answer 1

(Leaving this here for now, but see edit.)

Do you know a implementation of lock free queue in C?

I wrote lockless queue recently (http://www.ideone.com/l2QRp). I can't actually guarantee it works correctly, but I can't find any bugs and I've used it in a couple of single threaded programs without any problems, so there's nothing too obvious wrong with it.

Trivial usage example:

queue_t queue;
int val = 42;
queue_init(&queue,sizeof val);
queue_put(&queue,&val);
val = 0; 
queue_pop(&queue,&val);
printf("%i\n",val); // 42
queue_destroy(&queue);

Edit:

As @Alexey Kukanov pointed out, queue_pop can fail if tmp is popped,freed,allocated again, and put again between checking for null and swapping:

    if(!tmp->next) return errno = ENODATA;
    /* can fail here */
    } while(!sync_swap(q->head,tmp,tmp->next));

I'm not yet sure how to fix this, but I'll (hopefully) update this once I figure it out. For now, disregard this.