On Fri, 29 Dec 2023 at 21:07, Richard Guo <guofengli...@gmail.com> wrote: > It seems to me that the former scenario also makes sense in some cases. > For instance, let's say there are two pointers in two structs, s1->p and > s2->p, both referencing the same bitmapset. If we modify the bitmapset > via s1->p (even if no reallocation could occur), s2 would see different > content via its pointer 'p'.
That statement simply isn't true. If there's no reallocation then both pointers point to the same memory and, therefore have the same content, not different content. In the absence of a reallocation, then the only time s1->p and s2->p could differ is if s1->p became an empty set as a result of the modification. > Sometimes this is just wrong and could > cause problems. If we can force a reallocation for every modification > of the bitmapset, it'd be much easier to find such bugs. Whether it's intended or unintended, at least it's consistent, therefore isn't going to behave differently if the number of bitmapwords in the set changes. All REALLOCATE_BITMAPSETS does for bms_int_members(), bms_join() and bms_del_members() is change one consistent behaviour (we never reallocate) into some other consistent behaviour (we always reallocate). If we make REALLOCATE_BITMAPSETS work how I propose in my patch then the reallocation is just limited to cases where the set *could* be repalloced by a modification. That change gives us consistent behaviour as the set is *always* reallocated when it *could* be reallocated. Making it consistent to me, seems good as a debug option. Swapping one consistent behaviour for another (as you propose) seems pointless and more likely to force us to change code that works perfectly fine today. In any case, the comments in bms_int_members(), bms_join() and bms_del_members() are now only true when REALLOCATE_BITMAPSETS is not defined. Are you proposing we leave those comments outdated? or do you propose that we mention that the left inputs are not recycled when building with REALLOCATE_BITMAPSETS? In my view, neither of these is acceptable as often the primary reason to use something like bms_int_members() over bms_intersect() is exactly because the left input is recycled. I don't want people to have to start contorting code because bms_int_members()'s left input recycling cannot be relied on. David
