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

  The _REMQHI function removes the first entry from the queue in an
  indivisible manner.  This operation is interlocked against similar
  operations by other processors or devices in the system.

  Syntax:

       typedef enum {_remqi_removed_more, _remqi_not_removed,
                     _remqi_removed_empty, _remqi_empty}
                     _REMQI_STATUS;

       _REMQI_STATUS _REMQHI(void *__head), void *__removed_entry);