VMS Help POSIX Threads, PTHREAD routines, pthread_setspecific, Return Values  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    If an error condition occurs, this routine returns an integer
    indicating the type of error. Possible return values are as
    follows:

    Return      Description

    0           Successful completion.
    [EINVAL]    The specified key is invalid.
    [ENOMEM]    Insufficient memory to associate the value with the
                key.