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

 key

    Location where the new thread-specific data key will be stored.

 destructor

    Procedure called to destroy a thread-specific data value
    associated with the created key when the thread terminates.
    Note that the argument to the destructor for the user-specified
    routine is the non-NULL value associated with a key.