Message-ID: <482E2007.6050502@esilo.com>
Date: Fri, 16 May 2008 20:00:07 -0400
From: Andrew Chernow <ac@esilo.com>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: Merlin Moncure <mmoncure@gmail.com>, Andrew Dunstan <andrew@dunslane.net>,
	Alvaro Herrera <alvherre@commandprompt.com>,
	"Patches (PostgreSQL)" <pgsql-patches@postgresql.org>
Subject: Re: libpq object hooks
References: <b42b73150804301323i18b00019i62e765708abb65aa@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> <482CD76E.6000202@esilo.com>
	<b42b73150805160628y3c175608hc383187951206448@mail.gmail.com>
	<17177.1210949948@sss.pgh.pa.us> <482DD3AC.9020207@esilo.com>
	<b42b73150805161249wb67b065le957ef1c0cdaefec@mail.gmail.com>
	<20531.1210969396@sss.pgh.pa.us>
In-Reply-To: <20531.1210969396@sss.pgh.pa.us>
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Tom Lane wrote:
> Where
> exactly does the hook hand off the storage pointer to libpq?  What
> are you going to do if the hook fails to create the storage
> (ie, out of memory during PGresult creation)?

The current submitted patch has 3 of its function callbacks returning a 
void*, initHookData after the creation of a conn, resultCreate, and 
resultCopy.  We have recently changed this design so all hooks, now 
called events, go through a single callback ... PGEventProc.  The old 
function callbacks are just eventIds now.

/////////////////////////////////
// The libpq side (looping registered event procs)
PGEventResultCreate info;
info.stateData = NULL; /* our event data ptr */
info.conn = conn;
info.result = result;

if(!result->evtState[i].proc(PGEVT_RESULTCREATE,
   (void *)&info, result->evtState[i].passThrough)
{
   PQclear(result); // destroy result? ... not sure
   return error;    // previously, we ignored it
}

// assign event data created by event proc.
result->evtState[i].data = info.stateData;


///////////////////////////////////////
// example of what the event proc does
int my_evtproc(PGEventId evtId, void *evtInfo, void *passThrough)
{
   switch(eventId)
   {
     case PGEVT_RESULTCREATE:
     {
       void *data = makeresultdata(....)
       if(!data)
         return FALSE;
       ((PGEventResultCreate *)evtInfo)->stateData = data;
       break;
     }
   }

   return TRUE;
}


-- 
Andrew Chernow
eSilo, LLC
every bit counts
http://www.esilo.com/

-- 
Andrew Chernow
eSilo, LLC
every bit counts
http://www.esilo.com/