(* Library module defined by the International Standard
   Information technology - programming languages
   BS ISO/IEC 10514-1:1996E Part 1: Modula-2, Base Language.

   Copyright ISO/IEC (International Organization for Standardization
   and International Electrotechnical Commission) 1996-2021.

   It may be freely copied for the purpose of implementation (see page
   707 of the Information technology - Programming languages Part 1:
   Modula-2, Base Language.  BS ISO/IEC 10514-1:1996).  *)

DEFINITION MODULE COROUTINES;

(* Facilities for coroutines and the handling of interrupts *)

IMPORT SYSTEM ;


CONST
  UnassignedPriority = 0 ;

TYPE
  COROUTINE ; (* Values of this type are created dynamically by NEWCOROUTINE
                 and identify the coroutine in subsequent operations *)
  INTERRUPTSOURCE = CARDINAL ;
  PROTECTION = [UnassignedPriority..7] ;


PROCEDURE NEWCOROUTINE (procBody: PROC;
                        workspace: SYSTEM.ADDRESS;
                        size: CARDINAL;
                        VAR cr: COROUTINE;
                        [initProtection: PROTECTION = UnassignedPriority]);
  (* Creates a new coroutine whose body is given by procBody, and
     returns the identity of the coroutine in cr. workspace is a
     pointer to the work space allocated to the coroutine; size
     specifies the size of this workspace in terms of SYSTEM.LOC.

     The optarg, initProtection, may contain a single parameter which
     specifies the initial protection level of the coroutine.
  *)

PROCEDURE TRANSFER (VAR from: COROUTINE; to: COROUTINE);
  (* Returns the identity of the calling coroutine in from, and
     transfers control to the coroutine specified by to.
  *)

PROCEDURE IOTRANSFER (VAR from: COROUTINE; to: COROUTINE);
  (* Returns the identity of the calling coroutine in from and
     transfers control to the coroutine specified by to.  On
     occurrence of an interrupt, associated with the caller, control
     is transferred back to the caller, and the identity of the
     interrupted coroutine is returned in from.  The calling coroutine
     must be associated with a source of interrupts.
  *)

PROCEDURE ATTACH (source: INTERRUPTSOURCE);
  (* Associates the specified source of interrupts with the calling
     coroutine. *)

PROCEDURE DETACH (source: INTERRUPTSOURCE);
  (* Dissociates the specified source of interrupts from the calling
     coroutine. *)

PROCEDURE IsATTACHED (source: INTERRUPTSOURCE): BOOLEAN;
  (* Returns TRUE if and only if the specified source of interrupts is
     currently associated with a coroutine; otherwise returns FALSE.
  *)

PROCEDURE HANDLER (source: INTERRUPTSOURCE): COROUTINE;
  (* Returns the coroutine, if any, that is associated with the source
     of interrupts. The result is undefined if IsATTACHED(source) =
     FALSE.
  *)

PROCEDURE CURRENT (): COROUTINE;
  (* Returns the identity of the calling coroutine. *)

PROCEDURE LISTEN (p: PROTECTION);
  (* Momentarily changes the protection of the calling coroutine to
     p. *)

PROCEDURE PROT (): PROTECTION;
  (* Returns the protection of the calling coroutine. *)


(*
   TurnInterrupts - switches processor interrupts to the protection
                    level, to.  It returns the old value.
*)

PROCEDURE TurnInterrupts (to: PROTECTION) : PROTECTION ;


(*
   ListenLoop - should be called instead of users writing:

                LOOP
                   LISTEN
                END

                It performs the same function but yields
                control back to the underlying operating system.
                It also checks for deadlock.
                Note that this function does return when an interrupt occurs.
                (File descriptor becomes ready or time event expires).
*)

PROCEDURE ListenLoop ;


END COROUTINES.