VMS Help CC, Language topics, Builtin Functions, Insert Entry into Queue at Head Interlocked  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The _INSQHI function inserts an entry into the front of a queue in
  an indivisible manner.  This operation is interlocked against
  similar operations by other processors or devices in the system.

  Syntax:

       typedef enum {_insqi_inserted_many, _insqi_not_inserted,
                     _insqi_inserted_only} _INSQI_STATUS;

       _INSQI_STATUS _INSQHI(void *__new_entry, void *__head);