The GNU Modula-2 front end to GCC

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.
  *)

END Processes.