event-id

    OpenVMS usage identifier
    type          longword (unsigned)
    access        read only
    mechanism     by reference
    Identifier of the event. The event-id argument is the address of
    an unsigned longword containing the identifier.

    Event-id is returned by PPL$CREATE_EVENT.

 astadr

    OpenVMS usage ast_procedure
    type          procedure value
    access        call without stack unwinding
    mechanism     by reference
    AST routine. The astadr argument is a procedure value of the
    user's AST routine. This routine is called on the user's behalf
    when the event state becomes occurred.

 astprm

    OpenVMS usage user_arg
    type          unspecified
    access        read only
    mechanism     by value
    AST value passed as the argument to the specified AST routine.
    The astprm argument is the address of a vector of unsigned
    longwords containing this optional value. If this argument is not
    specified, PPL$_EVENT_OCCURRED is the astprm for a user-created
    event. The astprm argument has special restrictions when used in
    conjunction with the PPL$ event routines.

    o  For user-defined events, the AST-argument must point to a
       vector of two unsigned longwords. The first longword is a
       "context" reserved for the user; it is not read or modified
       by PPL$. The second longword receives the value specified by
       the event-param argument in the call to PPL$TRIGGER_EVENT that
       results in the delivery of this AST.

    o  For PPL$-defined events (those not created by the user),
       the astprm argument must point to a vector of four unsigned
       longwords. The vector accommodates the following:

       -  The user's "context" longword

       -  The longword to receive the event's distinguishing
          condition value

       -  The parameters to the PPL$-defined event (the "trigger"
          parameter)

       Because each of the predefined events takes two arguments, the
       vector that astprm points to must be four longwords in length.