Re: [PATCHES] libpq type system 0.9a - Mailing list pgsql-hackers

Andrew Chernow wrote:
> 
> Any thoughts on the hooking suggested by Tom?  It sounds like it should 
> be generic enough so more than just libpqtypes can make use of it.  I 
> think something of this nature should have input before I do anything.
> 
> Possible Hook points: (at least ones needed by libpqtypes)
> conn_create
> conn_reset
> conn_destroy
> result_create
> result_destroy
> 
> I guess libpqtypes would have to maintain a map of conns and results?  
> Right now it can associate type info because we added members to conn 
> and result.  When conn_create(conn) is called, libpqtypes would need to 
> map this by pointer address (as it is all it has as an identifier).  
> Still feels like maybe there should be a void* in a conn and result used 
> for per-connection/result based info (libpqtypes or not).
> 

Well, I can get it working with a very small patch.  We actually don't need very 
much in libpq.  Although, making it somehow generic enough to be useful to other 
extensions is a bit tricky.  Please, suggestions would be helpful.

Below is a raw shell of an idea that will work for libpqtypes.  Start by 
removing our entire patch and then add the below:

// libpqtypes only needs the below.  could add op_reset,
// op_linkerror, etc...
enum
{  HOOK_OP_CREATE,  HOOK_OP_DESTROY
};

struct pg_conn
{  // everything currently in a pg_conn  // ...
  // libpqtypes needs HOOK_OP_DESTROY, a ptr to hookData  // is always used in case the hooklib needs to allocate  //
orreallocate the hookData.  void *hookData;  int (*connHook)(PGconn *conn, int op, void **hookData);
 
}

struct pg_result
{  // everything currently in a pg_result  .....
  // libpqtypes needs create & destroy  // conn is NULL for destroy  void *hookData;  int (*resultHook)(PGconn *conn,
PGresult*result,    int op, void **hookData);
 
}

freePGconn(PGconn *conn)
{  // ...  if(conn->connHook)    conn->connHook(conn, HOOK_OP_DESTROY, &conn->hookdata);  // ...
}

PQmakeEmptyPGresult(PGconn *conn, ExecStatusType status)
{  // ... (result allocated here)  if(result->resultHook)    result->resultHook(conn, result,      HOOK_OP_CREATE,
&result->hookData); // ...
 
}

PQclear(PGresult *result)
{  // ...  if(result->resultHook)    result->resultHook(NULL, result,      HOOK_OP_DESTROY, &result->hookdata);  //
...
}

// library wide
int PQregisterHooks(connHook, resultHook);

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