(*$R-*)IMPLEMENTATION MODULE Processes [1];(*  Module:       Processes  From:         "Programming in Modula-2", 3rd, corrected edition, by N. Wirth  Version:      $Header: /cvsup/minix/src/lib/libm2/Processes.mod,v 1.1.1.1 2005/04/21 14:56:21 beng Exp $*)  FROM	SYSTEM IMPORT	ADDRESS, TSIZE, NEWPROCESS, TRANSFER;  FROM	Storage IMPORT	Allocate;  FROM	Traps IMPORT	Message;  TYPE	SIGNAL = POINTER TO ProcessDescriptor;	ProcessDescriptor =		RECORD	next: SIGNAL;	(* ring *)			queue: SIGNAL;	(* queue of waiting processes *)			cor: ADDRESS;			ready: BOOLEAN;		END;  VAR	cp: SIGNAL;			(* current process *)  PROCEDURE StartProcess(P: PROC; n: CARDINAL);    VAR	s0: SIGNAL;	wsp: ADDRESS;  BEGIN	s0 := cp;	Allocate(wsp, n);	Allocate(cp, TSIZE(ProcessDescriptor));	WITH cp^ DO		next := s0^.next;		s0^.next := cp;		ready := TRUE;		queue := NIL	END;	NEWPROCESS(P, wsp, n, cp^.cor);	TRANSFER(s0^.cor, cp^.cor);  END StartProcess;  PROCEDURE SEND(VAR s: SIGNAL);    VAR	s0: SIGNAL;  BEGIN	IF s # NIL THEN		s0 := cp;		cp := s;		WITH cp^ DO			s := queue;			ready := TRUE;			queue := NIL		END;		TRANSFER(s0^.cor, cp^.cor);	END  END SEND;  PROCEDURE WAIT(VAR s: SIGNAL);    VAR	s0, s1: SIGNAL;  BEGIN	(* insert cp in queue s *)	IF s = NIL THEN		s := cp	ELSE		s0 := s;		s1 := s0^.queue;		WHILE s1 # NIL DO			s0 := s1;			s1 := s0^.queue		END;		s0^.queue := cp	END;	s0 := cp;	REPEAT		cp := cp^.next	UNTIL cp^.ready;	IF cp = s0 THEN		(* deadlock *)		Message("deadlock");		HALT	END;	s0^.ready := FALSE;	TRANSFER(s0^.cor, cp^.cor)  END WAIT;  PROCEDURE Awaited(s: SIGNAL): BOOLEAN;  BEGIN	RETURN s # NIL  END Awaited;  PROCEDURE Init(VAR s: SIGNAL);  BEGIN	s := NIL  END Init;BEGIN	Allocate(cp, TSIZE(ProcessDescriptor));	WITH cp^ DO		next := cp;		ready := TRUE;		queue := NIL	ENDEND Processes.