The Stop a Participant routine terminates the execution of the
    specified participant in this application.
    Format
      PPL$STOP  participant-index
1 – Arguments
 participant-index
    OpenVMS usage longword_unsigned
    type          longword (unsigned)
    access        read only
    mechanism     by reference
    PPL$-defined index of the participant to be terminated. The
    participant-index argument is the address of an unsigned longword
    containing the index.
    Participant-index is obtained by a call to PPL$SPAWN or PPL$GET_
    INDEX.