The POSIX Threads Library is VSI's multithreading run-time
    library package. It offers access to library routines via several
    interfaces. The Threads Library offers two primary interfaces:

    o  The PTHREAD multithreading interface is VSI's implementation
       of the IEEE POSIX 1003.1-1996 standard. Use this interface to
       build portable, multithreaded applications.

    o  The proprietary TIS interface offers routines that provide
       "thread-independent services." These routines allow a program
       to perform (or a library to offer) thread-safe processing that
       requires synchronization, but without requiring the use of
       threads.

    A thread is a single, sequential flow of control within a
    program. Use threads to improve a program's performance-that
    is, its throughput, computational speed, responsiveness, or some
    combination. Multiple threads are useful in a multiprocessor
    system, where a program's threads can run concurrently on
    separate processors. On single-processor systems, multiple
    threads can also improve a program's performance by permitting
    the overlap of input, output, or other slow operations with
    computational operations. For more information see the Guide
    to the POSIX Threads Library documentation.