SCHEDULE.DEF

DEFINITION MODULE Schedule;
(******************************************************************************)
(* This is the scheduler module.  This shows Modula-2's operating system      *)
(* characteristics.  Modula-2 was originally created as a systems programming *)
(* language.  The CPU clock vector interrupt is overwritten and the schedular *)
(* code is put in its place.                                                  *)
(* By Fritz Feuerbacher                                                       *)
(******************************************************************************)

EXPORT QUALIFIED Semaphore, MakeReady, Scheduler, Terminate, InitSem, P, V;

TYPE Semaphore;

PROCEDURE MakeReady(proc : PROC; wkspSize : CARDINAL);
   (* prepares a process for execution *)

PROCEDURE Scheduler;
   (* begins execution of processes that have been prepared by previous
      calls of MakeReady *)

PROCEDURE Terminate;
  (* terminates the current process *)

PROCEDURE InitSem(VAR sem : Semaphore; value : CARDINAL);
  (* initializes a semaphore by setting its count to "value"
     and making its queue empty *)

PROCEDURE P( VAR sem : Semaphore );
   (* decrements semaphore count; if count is less than zero then the
      current process is suspended and put on the semaphore queue *)

PROCEDURE V( VAR sem : Semaphore );
  (* increments semaphore count; if count is less than or equal to zero,
     it then enables a process on the semaphore queue                 *)

END Schedule.