Re: external function proposal for 7.2

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.
> 



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