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

#### 4.4.30 gm2-libs-iso/Processes ¶

    DEFINITION MODULE Processes;

      (* This module allows concurrent algorithms to be expressed using
         processes. A process is a unit of a program that has the
         potential to run in parallel with other processes.
      *)

    IMPORT SYSTEM;

    TYPE
      ProcessId;                      (* Used to identify processes *)
      Parameter     = SYSTEM.ADDRESS; (* Used to pass data between processes *)
      Body          = PROC;           (* Used as the type of a process body *)
      Urgency       = INTEGER;        (* Used by the internal scheduler *)
      Sources       = CARDINAL;       (* Used to identify event sources *)
      ProcessesExceptions =           (* Exceptions raised by this module *)
        (passiveProgram, processError);

    (* The following procedures create processes and switch control between
       them. *)

    PROCEDURE Create (procBody: Body; extraSpace: CARDINAL; procUrg: Urgency;
                      procParams: Parameter; VAR procId: ProcessId);
      (* Creates a new process with procBody as its body, and with urgency
         and parameters given by procUrg and procParams.  At least as
         much workspace (in units of SYSTEM.LOC) as is specified by
         extraSpace is allocated to the process.
         An identity for the new process is returned in procId.
         The process is created in the passive state; it will not run
         until activated.
      *)

    PROCEDURE Start (procBody: Body; extraSpace: CARDINAL; procUrg: Urgency;
                     procParams: Parameter; VAR procId: ProcessId);
      (* Creates a new process, with parameters as for Create.
         The process is created in the ready state; it is eligible to
         run immediately.
      *)

    PROCEDURE StopMe ();
      (* Terminates the calling process.
         The process must not be associated with a source of events.
      *)

    PROCEDURE SuspendMe ();
      (* Causes the calling process to enter the passive state.  The
         procedure only returns when the calling process is again
         activated by another process.
      *)

    PROCEDURE Activate (procId: ProcessId);
      (* Causes the process identified by procId to enter the ready
         state, and thus to become eligible to run again.
      *)

    PROCEDURE SuspendMeAndActivate (procId: ProcessId);
      (* Executes an atomic sequence of SuspendMe() and
         Activate(procId). *)

    PROCEDURE Switch (procId: ProcessId; VAR info: Parameter);
      (* Causes the calling process to enter the passive state; the
         process identified by procId becomes the currently executing
         process.  info is used to pass parameter information from the
         calling to the activated process.  On return, info will
         contain information from the process that chooses to switch
         back to this one (or will be NIL if Activate or
         SuspendMeAndActivate are used instead of Switch).
      *)

    PROCEDURE Wait ();
      (* Causes the calling process to enter the waiting state.
         The procedure will return when the calling process is
         activated by another process, or when one of its associated
         eventSources has generated an event.
      *)

    (* The following procedures allow the association of processes
       with sources of external events.
    *)

    PROCEDURE Attach (eventSource: Sources);
      (* Associates the specified eventSource with the calling
         process. *)

    PROCEDURE Detach (eventSource: Sources);
      (* Dissociates the specified eventSource from the program. *)

    PROCEDURE IsAttached (eventSource: Sources): BOOLEAN;
      (* Returns TRUE if and only if the specified eventSource is
         currently associated with one of the processes of the
         program.
      *)

    PROCEDURE Handler (eventSource: Sources): ProcessId;
      (* Returns the identity of the process, if any, that is
         associated with the specified eventSource.
      *)

    (* The following procedures allow processes to obtain their
       identity, parameters, and urgency.
    *)

    PROCEDURE Me (): ProcessId;
      (* Returns the identity of the calling process (as assigned
         when the process was first created).
      *)

    PROCEDURE MyParam (): Parameter;
      (* Returns the value specified as procParams when the calling
         process was created. *)

    PROCEDURE UrgencyOf (procId: ProcessId): Urgency;
      (* Returns the urgency established when the process identified
         by procId was first created.
      *)

    (* The following procedure provides facilities for exception
       handlers. *)

    PROCEDURE ProcessesException (): ProcessesExceptions;
      (* If the current coroutine is in the exceptional execution state
         because of the raising of a language exception, returns the
         corresponding enumeration value, and otherwise raises an
         exception.
      *)

    PROCEDURE IsProcessesException (): BOOLEAN;
      (* Returns TRUE if the current coroutine is in the exceptional
         execution state because of the raising of an exception in
         a routine from this module; otherwise returns FALSE.
      *)

    (*
       Reschedule - rotates the ready queue and transfers to the process
                    with the highest run priority.
    *)

    PROCEDURE Reschedule ;

    (*
       displayProcesses -
    *)

    PROCEDURE displayProcesses (message: ARRAY OF CHAR) ;

    END Processes.