Hi, On 2020-08-07 12:29:03 -0400, Robert Haas wrote: > On Thu, Aug 6, 2020 at 11:46 PM Bharath Rupireddy > <bharath.rupireddyforpostg...@gmail.com> wrote: > > I sent the patch previously[1], but attaching here again, modifies > > cancel_before_shmem_exit() function comment to reflect the safe usage > > of before_shmem_exit_list callback mechanism and also removes the > > point "For simplicity, only the latest entry can be removed*********" > > as this gives a meaning that there is still scope for improvement in > > cancel_before_shmem_exit() search mechanism. > > > > Thoughts? > > I think that the first part of the comment change you suggest is a > good idea and would avoid developer confusion, but I think that the > statement about unordered removal of comments being risky doesn't add > much. It's too vague to help anybody and I don't think I believe it, > either. So I suggest something more like: > > - * callback. For simplicity, only the latest entry can be > - * removed. (We could work harder but there is no need for > - * current uses.) > + * callback. We only look at the latest entry for removal, as we > + * expect the caller to use before_shmem_exit callback mechanism > + * in the LIFO order.
In which situations is the removal actually useful *and* safe, with these constraints? You'd have to have a very narrow set of functions that are called while the exit hook is present, i.e. basically this would only be usable for PG_ENSURE_ERROR_CLEANUP and nothing else. And even there it seems like it's pretty easy to get into a situation where it's not safe. Greetings, Andres Freund
