On Mon, Aug 8, 2016 at 8:53 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Thomas Munro <thomas.mu...@enterprisedb.com> writes: >> Yeah, I was considering unbalanced pin/unpin requests to be a >> programming error. To be more defensive about that, how about I add a >> boolean 'pinned' to dsm_control_item, and elog(ERROR, ...) if it's not >> in the expected state when you try to pin or unpin? > > Well, what you have there is a one-bit-wide pin request counter. > I do not see why that's better than an actual counter, but if that's > what you want to do, fine. > > The larger picture here is that Robert is exhibiting a touching but > unfounded faith that extensions using this feature will contain zero bugs.
That's an overstatement of my position. I think it is quite likely that extensions using this feature will have bugs, because essentially all code has bugs, but whether they are likely have the specific bug of unpinning a segment that is already unpinned is not quite so clear. That's not to say I object to Thomas's v2 patch, which will catch that mistake if it happens. Defensive programming never killed anybody, as far as I know. However, I don't see the need for a full-blown request counter here; we've had this API for several releases now and to my knowledge nobody has complained about the fact that you aren't supposed to call dsm_pin_segment() multiple times for the same segment. Therefore, I think the evidence supports the contention that it's not broken and doesn't need to be fixed. If we do decide it needs to be fixed, I think that's material for a separate patch. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
