Pth is a very portable POSIX/ANSI-C based library for Unix platforms
which provides non-preemptive priority-based scheduling for multiple
threads of execution ("multithreading") inside server applications.
All threads run in the same address space of the server application,
but each thread has it's own individual program-counter, run-time
stack, signal mask and errno variable.
pthsem is an extend version, with support for semaphores added. It can
be installed parallel to a normal pth. The header file is called pthsem.h,
the configuration program pthsem-config and the autoconf macro
AC_CHECK_PTHSEM.