Threading for 7.5

As you know, we had libpq and ecpg threading available in 7.4 via a
configure flag.

However, threading required users to report their platform's configure
flags (something better done by configure) and run a thread test program
(src/tools/thread/thread_test).

For 7.5, I want to use:

http://www.gnu.org/software/ac-archive/htmldoc/acx_pthread.html

that Jan found that is a plug-in for configure to determine thread
flags. As long as it has the existing platform flags we know about,
this will be a better way to determine threading flags.

The thread-test program is works, but it tests only one version of each
operating system. Ideally is should be run on the build/install
machine, rather than have a per-port value. I talked via chat with
Peter on this, and running this from configure again only tests the
current library, and doesn't handle cross-compiling or cases where a
different version of the dynamic library is used for binary
distributions.

The basic problem is that thread_test tests _how_ functions get their
results (thread-safe or not), and not the actual input/output of the
function.

I want to do away with per-platform testing for thread_test. If the
platform supports threading, it should pass that test. I have updated
its output to be cleaner:

Make sure you have added any needed 'THREAD_CPPFLAGS' and 'THREAD_LIBS'
defines to your template/$port file before compiling this program.

errno is thread-safe

Your system uses strerror() which is thread-safe.
Your system has getpwuid_r(), so it doesn't use getpwuid().
Your system has getaddrinfo(), so it doesn't use gethostbyname()
or gethostbyname_r().

YOUR PLATFORM IS THREADSAFE

It reports the system as thread safe or not thread-safe. I think we can
just tell folks to run that test if they are going to use threads or if
they are having problems with threads. We can mark platform versions
that are _not_ thread safe, rather than enable platforms only after they
have passed the test. If it doesn't pass, the platform is broken for
threads. The idea is that any platform that supports threads _should_
pass the test. Assuming that many will fail is not efficient for us,
and perhaps not reliable either.

Peter asked about binary-only distributions, and how they would run the
thread test program. Perhaps when threading is enabled in configure, we
should actually install the thread test program as pg_thread_test in
/bin along with the other PostgreSQL binaries. Folks who want to use
threads should run that program first to test things.

With these changes, all platforms should be able to enable threads, and
we will not have to collect per-platform thread reports for 7.5, except
collect platform versions that are not thead-safe and put those tests in
the template files.

Comments?

--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
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