Re: Detecting libpq connections improperly shared via fork()

On Thu, Oct 04, 2012 at 12:14:02AM +0200, Andres Freund wrote:
> On Thursday, October 04, 2012 12:08:18 AM Daniel Farina wrote:
> > It would be fantastic for libpq to somehow monitor use of a connection
> > from multiple PIDs that share a parent and deliver an error indicating
> > what is wrong. Unfortunately detecting that would require either a
> > file or some kind of shared memory map, AFAIK, and I don't know how
> > keen anyone is on accepting that patch. So, may I ask: how keen is
> > anyone on accepting such a patch, and under what conditions of
> > mechanism?
> Hm. An easier version of this could just be storing the pid of the process
> that did the PQconnectdb* in the PGconn struct. You can then check that
> PGconn->pid == getpid() at relatively few places and error out on a mismatch.
> That should be doable with only minor overhead.

On system's that support it, pthread_atfork() might help. Though being
like a signal handler you don't have access to the PGconn structure, so
you can't flag anything easily. Maybe just to cache getpid()?

In any case, adding a check to PQexec and friends would probably be
sufficient, since that's what every program is going to start with.

Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> He who writes carelessly confesses thereby at the very outset that he does
> not attach much importance to his own thoughts.
-- Arthur Schopenhauer