The HP proprietary TIS interface provides routines that you use
    to build thread-safe libraries whose own routines do not create
    threads, but which can safely be called from a multithreaded
    environment. TIS routines are functionally identical to their
    corresponding routines in the PTHREAD interface. See the Guide to
    the POSIX Threads Library documentation for more information.

    In a program that creates threads, TIS routines provide full
    thread synchronization and memory coherence. But, when run in
    a program that does not use threads, the same TIS calls provide
    low-overhead "stub" implementations of PTHREAD features. That
    is, the objects created using the TIS interface are the same as
    PTHREAD objects. When threads are present, the guidelines for
    using PTHREAD routines apply also to the use of the corresponding
    TIS routine.