Question about Linux, threads, and Postgres

I've been running various versions of Postgres for several years now,
including one prototype web site for a customer. I currently run
6.3.2 at home, and will upgrade to 6.4.2, but I have some questions.

I am programming on Linux 2.0, libc6, in C.

I am writing a server application to sit between the database and
clients. I would like to thread it. This is strictly a home
education application, so I don't mind experimenting. I have written
some small threaded apps before, but nothing fancy. In particular, I
have never used any "third party" libraries; it has all been my code
and general libc stuff.

The Linux thread documentation mentions problems using X libraries
which have been compiled without threading support, either designed-in
or even using the compile time flag _REENTRANT. As long as only one
thread calls all non-threaded functions, errno itself is safe, because
all the threaded code uses a per-thread value, leaving the global
errno to the unthreaded code. I would not be surprised to find there
are other global variables also abused this way :-)

Q 1: Does anyone have experience with Postgres in a threaded program?

Q 2: Is it necessary and/or sufficient to have only one thread talk to
the Postgres library?

Q 3: Would it be good / bad to compile 6.4.2 with -D_REENTRANT, and
would this help with Q#2?

I searched the archives, but variations on "thread" found nothing but
references to threaded mailing list archives :-)

I also saw the news about 6.5 going from table locks to no locks.
This sounds pretty exciting! I think it will be fun to write some
test programs for that, leave my box thrashing on it for a while when
I go to work :-) But I have to find the usual spare time first :-(

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