On Fri, May 16, 2008 at 10:59 AM, Tom Lane <[EMAIL PROTECTED]> wrote: > "Merlin Moncure" <[EMAIL PROTECTED]> writes: >>> typedef void *(*PGobjectEventProc)(PGobjectEventId evtId, ...); >>> int PQregisterObjectEventProc(PGconn*, PGobjectEventProc); >>> void *PQeventData(PGconn *, PGobjectEventProc); >>> void *PQresultEventData(PGresult *, PGobjectEventProc); > >> This provides what we need...a key to lookup the hook data without >> using a string. Also, it reduces the number of exports (it's a little >> easier for us, while not essential, to not have to register each >> callback individually). Also, this AFAICT does not have any ABI >> issues (no struct), and adds less exports which is nice. We don't >> have to 'look up' the data inside the callbacks..it's properly passed >> through as an argument. While vararg callbacks may be considered >> unsafe in some scenarios, I think it's a good fit here. > > I don't think varargs callbacks are a good idea at all. Please adjust > this to something that doesn't do that. Also, haven't you forgotten > the passthrough void *?
We didn't...one of the functions (the init) doesn't need it so we didn't expose it to the fixed arguments...we would just va_arg it off in the other cases. Regardless, your comments below make that moot: > If you really want only one callback function, perhaps what would work > is > > typedef void (*PGeventProc) (PGeventId eventId, const void *eventInfo, > void *passthrough); > > int PQregisterEventProc(PGconn *conn, PGeventProc proc, void *passthrough); > > where eventInfo will point to one of several exported struct types > depending on the value of eventId. With this approach, you can add > more fields to the end of any one such struct type without creating > ABI issues. I have little confidence in being able to make similar > changes in a varargs environment. this is fine. > Also, even if varargs are safe they'd be notationally unpleasant > in the extreme. varargs are just a PITA to work with --- you'd have > to do all the decoding in the first-level hook routine, even for > items you weren't going to use. With something like the above > all you need is a switch() and some pointer casts. Switch, plus struct (basically a union) will do the trick nicely. Can it be a formal union, or is it better as a void*? The main issue was how what we called the 'hook data' was passed back and forth. We'll get a patch up. merlin -- Sent via pgsql-patches mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-patches