[3.4-dev] Obscure bug with queues

[PowerWyrm]

I didn't check all the calls to "struct queue" in the code, but the ones in generate.c and obj-util.c assume that the queue can handle "size" pointers when created with a size of "size".

When looking at the code in z-queue.c, pushing "size" items in a queue of size "size" will not work:

void q_push(struct queue *q, uintptr_t item) {
    q->data[q->tail] = item;
    q->tail = (q->tail + 1) % q->size;
    if (q->tail == q->head) abort();
}

For the last item, abort() will be called (which is quite ugly in itself -- it won't save the character state before quitting for example).

Fix: either allow one more item in the queue, or add +1 to queue size when calling q_new().

[d_m]

Originally Posted by PowerWyrm

For the last item, abort() will be called (which is quite ugly in itself -- it won't save the character state before quitting for example).

Fix: either allow one more item in the queue, or add +1 to queue size when calling q_new().

Ooh, good catch!

Yeah, it probably should call something else instead. I will fix this and also try to do something a bit more friendly.

[d_m]

OK, this is fixed in angband/master and v4/v4-master.

I chose to use (size + 1) in q_new so that if the user wants a queue of size 40 it allocates 41 buckets.

Thanks again for catching this!