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

We have definatly had requests for improved thread-safeness for libpq
and ecpg in the past, so whatever you can do would be a help. We say
libpq is thread-safe, but specifically mention the non-threadsafe calls
in the libpq documentation, or at least we should. We have been making
marginal thread-safe improvements over the years.

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Lee Kindness wrote:
> 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.
>
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