#include <stdio.h>
#include <stdlib.h>

int main() {
    int x = 23;
    int success = __sync_bool_compare_and_swap(&x, 23, 34);
    printf("Success? %d; value = %d\n", success, x);
    success = __sync_bool_compare_and_swap(&x, 33, 22);
    printf("Success? %d; value = %d\n", success, x);

    int oldval = __sync_fetch_and_add(&x, 1000);
    printf("Changed from %d to %d atomically\n", oldval, x);
    int newval = __sync_add_and_fetch(&x, 1000);
    printf("Changed to %d (was %d at time of change) atomically\n", x, newval);
    __sync_synchronize(); // no visible effect; a memory barrier
}


typedef struct node {
    double payload;
    struct node *next;
} node_t;

typedef struct {
    node_t *head, *tail;
} queue_t;

void atomic_add(queue_t *q, double value) {
    // make node
    node_t *new_node = malloc(sizeof(node_t));
    new_node->payload = value;
    new_node->next = NULL;
    
    for(;;) { // retry until success
#ifdef TAIL_BEFORE_LINK
        node_t *p = q->tail;
        // first update the tail pointer
        if (__sync_bool_compare_and_swap(&(q->tail), p, new_node)) {
            // on success, update next pointer of old tail
            p->next = new_node;
            break;
        }
#else // LINK_BEFORE_TAIL
        // first update the connectivity
        if (__sync_bool_compare_and_swap(&(q->tail->next), NULL, new_node)) {
            // on success, update tail
            q->tail = new_node;
            break;
        }
#endif
    }
}