As a lurker on the list this post caught my eye somewhat. I think this
would be excellent functionality to have in postgres, i was considering
doing something like this in a non intruse manner, by manipulating
_init() and _fini functions of shared libraries. But what you have
described below is a much better interface. In particular i was looking
at a way of getting async notifications when a row had been inserted, and
pasing out to my other applications enough data, to be able to query back
in for the complete row.
The ability to have an init/exit for an external function would be a big
win, you could even have the init() create a thread for passing results
to, and performing what ever voodoo magic you wanted.
i'll go back to lurking and listening now.
On Tue, 12 Dec 2000, mlw wrote:
> I think the newC function idea is pretty good, however, what would be
> great is just one more step of protocol, perhaps an API verson 2 or 3:
>
> One thing than makes writing a non-trivial function a bit problematic,
> and perhaps even less efficient, is that the function does not know when
> it is first run and when it is finished, and there is no facility to
> manage contextual information. This limits external functons having to
> be fairly simple, or overly complex.
>
> I propose that when the newC structure is allocated that a function
> specific "Init" function be called, and when the structure is being
> freed, calling a "Exit" function. The new C structure should also have a
> void pointer that allows persistent information to be passed around.
>
> typedef struct
> {
> FmgrInfo *flinfo; /* ptr to lookup info used for this call
> */
> Node *context; /* pass info about context of call */
> Node *resultinfo; /* pass or return extra info about
> result */
> bool isnull; /* function must set true if result is
> NULL */
> short nargs; /* # arguments actually passed */
> Datum arg[FUNC_MAX_ARGS]; /* Arguments passed to function */
> bool argnull[FUNC_MAX_ARGS]; /* T if arg[i] is actually NULL
> */
>
> void * userparam; /* to be used by he function */
>
> } FunctionCallInfoData;
> typedef FunctionCallInfoData* FunctionCallInfo;
>
> The userparam can be used to store data, or a count, or whatever.
>
> Datum function(PG_FUNCTION_ARGS) ;
> bool function_Init(PG_FUNCTION_ARGS);
> void function_Exit(PG_FUNCTION_ARGS);
>
> This protocol would make writing some really cool features much easier.
> As a C++ guy, I could execute "new" at Init and "delete" at Exit. ;-)
>
>
> Mark.
>
PGP key: http://codex.net/pgp/pgp.asc
