From: Andrew Chernow <ac@esilo.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Merlin Moncure <mmoncure@gmail.com>
Cc: Andrew Dunstan <andrew@dunslane.net>
Cc: Alvaro Herrera <alvherre@commandprompt.com>
Cc: Patches (PostgreSQL) <pgsql-patches@postgresql.org>
Subject: Re: libpq object hooks
Date: Thu, 15 May 2008 17:18:59 -0400
Message-ID: <482CA8C3.2000507@esilo.com> (raw)
In-Reply-To: <9867.1210877054@sss.pgh.pa.us>
References: <b42b73150804301323i18b00019i62e765708abb65aa@mail.gmail.com>
<482A58D8.2030205@dunslane.net>
<20080514043313.GS6966@alvh.no-ip.org>
<482AD896.4000504@dunslane.net>
<19342.1210776271@sss.pgh.pa.us>
<b42b73150805150852m7b3c28fai2d7a4497c84118b2@mail.gmail.com>
<6044.1210867771@sss.pgh.pa.us>
<482C77E5.1060500@esilo.com>
<9458.1210875556@sss.pgh.pa.us>
<482C82BA.3090100@esilo.com>
<9867.1210877054@sss.pgh.pa.us>
Tom Lane wrote:
> Andrew Chernow <ac@esilo.com> writes:
>> Which callback do we use as the key? Currently, none are required (only
>> the name was required). We have to choose one callback that must be
>> provided.
>
> What? I thought what you wanted back was the void * pointer that had
> been registered with a particular callback function. So you use that
> callback function. If it's not actually registered, you get a NULL.
>
>> This is what is passed to PQaddObjectHooks, along with a conn:
>
> This is all wrong IMHO, not least because it creates ABI problems if you
> want to add another hook type later. Register each hook separately, eg
>
> typedef void (*PGCRHook) (PGconn *conn, void *passthrough);
>
> void PQregisterConnResetHook(PGconn *conn, PQCRHook func, void *passthrough);
>
> ... repeat for each possible hook ...
>
> regards, tom lane
>
>
One can make a case to break apart the obj hooks structure into
individual register functions, but I think you have a different idea in
your head than what is being proposed. For starters, there is no
passthru pointer to register with a callback (there could be but that is
different than hook data...your register looks more like a user_ptr).
The passthru pointer, what we call hookData, is allocated with a PGconn
(not provided by the user). This is the point of the initHookData callback.
typedef void *(*PGinitHookData)(const PGconn *conn);
PQregisterInitHookData((PGconn *)NULL, (PGinitHookData)func);
PQregisterConnResetHook((PGconn *)NULL, (PGCRHook)func);
//etc...
conn = PQconnectdb();
When connectdb returns, initHookData has already been called. So, a
call to PQhookData(conn, ????) will work. BUT, what is still missing
from the equation is how to uniquely reference hookData on a conn.
What I was previously suggesting was to use the address of initHookData,
since w/o this address there wouldn't be any hook data to get. Seemed
like a logical choice.
--
Andrew Chernow
eSilo, LLC
every bit counts
http://www.esilo.com/
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To: pgsql-patches@postgresql.org
Cc: ac@esilo.com, tgl@sss.pgh.pa.us, mmoncure@gmail.com, andrew@dunslane.net, alvherre@commandprompt.com
Subject: Re: libpq object hooks
In-Reply-To: <482CA8C3.2000507@esilo.com>
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