gm2-libs-iso/COROUTINES (The GNU Modula-2 Compiler)

#### 4.4.1 gm2-libs-iso/COROUTINES ¶

    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.