Priorityqueue is buggy

[matthieugras]

My use case is that I use the pq as a reorder buffer for a fixed number of elements.
Each element in the pq has a timestamp (uint64) and some data.
New elements are pushed to the pq, if the pq has a certain size the top element is popped.
I also supplied a function to free the associated data.

while (!cpque_pq_val_empty(ctx->buf) &&
            cpque_pq_val_size(ctx->buf) > env.rob_size) {
  pq_val *curr = cpque_pq_val_top(&ctx->buf);
  consume_single_elem(ctx, curr->event_data);
  cpque_pq_val_pop(&ctx->buf);
}

This code seems to cause a problem. The order of the curr elements seems to be fine (smallest items first). But the order in which elements are freed by the pop call is inverted with respect to the priority (oldest elements are freed first).

[Tyge Løvset]

Thanks for reporting. Priority queue has been the least tested, and this was a silly bug that I think I have introduced a while back. Fixed in last commit.

[Tyge Løvset]

#include <stdio.h>

#define i_val int64_t
#define i_tag i
#define i_cmp -c_default_compare  // min-heap (increasing values)
#define i_del(x) printf("del %d\n", *(x))
#define i_from(x) (x)             // required because i_del is defined
#include <stc/cpque.h>

int main() {
    c_auto (cpque_i, heap)
    {
        c_apply(cpque_i, push, &heap, {231, 32, 873, 4, 343});

        puts("Extract the elements.");
        c_forrange (cpque_i_size(heap)) {
            printf("%zd ", *cpque_i_top(&heap));
            cpque_i_pop(&heap);
        }
    }
}

Gives correct output:

4 del 4
32 del 32
231 del 231
343 del 343
873 del 873