Function mi_abandoned_visited_revisit

3rd/mimalloc-2.0.9/src/segment.c:1111–1152

Move the visited list to the abandoned list.

// Move the visited list to the abandoned list.
static bool mi_abandoned_visited_revisit(void)
{
  // quick check if the visited list is empty
  if (mi_atomic_load_ptr_relaxed(mi_segment_t, &abandoned_visited) == NULL) return false;

  // grab the whole visited list
  mi_segment_t* first = mi_atomic_exchange_ptr_acq_rel(mi_segment_t, &abandoned_visited, NULL);
  if (first == NULL) return false;

  // first try to swap directly if the abandoned list happens to be NULL
  mi_tagged_segment_t afirst;
  mi_tagged_segment_t ts = mi_atomic_load_relaxed(&abandoned);
  if (mi_tagged_segment_ptr(ts)==NULL) {
    size_t count = mi_atomic_load_relaxed(&abandoned_visited_count);
    afirst = mi_tagged_segment(first, ts);
    if (mi_atomic_cas_strong_acq_rel(&abandoned, &ts, afirst)) {
      mi_atomic_add_relaxed(&abandoned_count, count);
      mi_atomic_sub_relaxed(&abandoned_visited_count, count);
      return true;
    }
  }

  // find the last element of the visited list: O(n)
  mi_segment_t* last = first;
  mi_segment_t* next;
  while ((next = mi_atomic_load_ptr_relaxed(mi_segment_t, &last->abandoned_next)) != NULL) {
    last = next;
  }

  // and atomically prepend to the abandoned list
  // (no need to increase the readers as we don't access the abandoned segments)
  mi_tagged_segment_t anext = mi_atomic_load_relaxed(&abandoned);
  size_t count;
  do {
    count = mi_atomic_load_relaxed(&abandoned_visited_count);
    mi_atomic_store_ptr_release(mi_segment_t, &last->abandoned_next, mi_tagged_segment_ptr(anext));
    afirst = mi_tagged_segment(first, anext);
  } while (!mi_atomic_cas_weak_release(&abandoned, &anext, afirst));
  mi_atomic_add_relaxed(&abandoned_count, count);
  mi_atomic_sub_relaxed(&abandoned_visited_count, count);
  return true;
}

// Push on the abandoned list.
static void mi_abandoned_push(mi_segment_t* segment) {