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From: Andrew Chernow <[email protected]>
To: Tom Lane <[email protected]>
Cc: Merlin Moncure <[email protected]>
Cc: Andrew Dunstan <[email protected]>
Cc: Alvaro Herrera <[email protected]>
Cc: Patches (PostgreSQL) <[email protected]>
Subject: Re: libpq object hooks
Date: Thu, 15 May 2008 17:18:59 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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Tom Lane wrote:
> Andrew Chernow <[email protected]> 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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