Re: PostgreSQL libraries - PThread Support, but not use...

Tom Lane writes:
> Lee Kindness <lkindness(at)csl(dot)co(dot)uk> writes:
> > On a slightly related note to the other threads thread [sic] going
> > on... Over the Christmas/New Year break i've been looking into making
> > the PostgreSQL client libraries (in particular libpq and ecpg)
> > thread-safe - that is they can safely be used by a program which
> > itself is using mutliple threads. I'm largely there with ecpg (globals
> > are protected, a sqlca for each thread), but of course it relies on
> > libpq which needs work to share a connection between thrreads.
>
> AFAIK, libpq is thread-safe already, it's just not thread-aware.
> What you'd presumably want is a wrapper layer that adds a mutex to
> prevent multiple threads from manipulating a PGconn at the same time.
> Couldn't this be done without touching libpq at all?

Certainly, it could. I've not fully investigated the current failings
of libpq WRT to threading yet. But it's certainly a bit more than I
stated above. I don't know where the statement that libpq is thread
safe originated from (I see it's on the website). but at a quick
glance I believe that krb4, krb5, PQoidStatus(),
PQsetClientEncoding(), winsock_strerror() need more though
investigation and non-thread-safe fuctions are also being used (at a
glance gethostbyname() and strtok()).

> > 1. It's looking likely that the libraries will need to link to
> > libpthread, and as a result anything linking to the libraries will
> > need to link to libpthread too. Will this be accepted in a patch?
> If the patch requires pthread and not any other form of thread support,
> probably not. See nearby threading thread ;-)
> In general I'd be unhappy with doing anything to libpq that forces
> non-threaded clients to start depending on libpthread (or other thread
> libraries). Thus the idea of a wrapper seems more appealing to me.

Okay, but what about ecpg? Thread-local sqlca instances would be a
real benefit, guess Michael and Christof are the guys to talk to?

I suppose the real problem is the needed baggage with this - the
autoconf macros will be a nightmare!

Thanks, Lee.