See the README.threads in the main perl 5.004_xx development
distribution (x >= 50) for details of how to build and use this.
If all else fails, read on.

If your version of patch can't create a file from scratch, then you'll
need to create an empty thread.h manually first.  Perl itself will need
to be built with -DUSE_THREADS yet. If you're using MIT pthreads or
another threads package that needs pthread_init() to be called, then
add -DNEED_PTHREAD_INIT. If you're using a threads library that only
follows one of the old POSIX drafts, then you'll probably need to add
-DOLD_PTHREADS_API. I haven't tested -DOLD_PTHREADS_API properly yet
and I think you may still have to tweak a couple of the mutex calls
to follow the old API.

This extension is copyright Malcolm Beattie 1995-1997 and is freely
distributable under your choice of the GNU Public License or the
Artistic License (see the main perl distribution).

Malcolm Beattie
mbeattie@sable.ox.ac.uk