(*$R-*)IMPLEMENTATION MODULE CSP;(*  Module:	Communicating Sequential Processes  From:		"A Modula-2 Implementation of CSP",		M. Collado, R. Morales, J.J. Moreno,		SIGPlan Notices, Volume 22, Number 6, June 1987.		Some modifications by Ceriel J.H. Jacobs  Version:	$Header: /cvsup/minix/src/lib/ack/libm2/CSP.mod,v 1.1 2005/10/10 15:27:46 beng Exp $   See this article for an explanation of the use of this module.*)  FROM random	IMPORT	Uniform;  FROM SYSTEM	IMPORT	BYTE, ADDRESS, NEWPROCESS, TRANSFER;  FROM Storage	IMPORT	Allocate, Deallocate;  FROM Traps	IMPORT	Message;  CONST	WorkSpaceSize = 2000;  TYPE	ByteAddress =	POINTER TO BYTE;	Channel =	POINTER TO ChannelDescriptor;	ProcessType =	POINTER TO ProcessDescriptor;	ProcessDescriptor = RECORD				next: ProcessType;				father: ProcessType;				cor: ADDRESS;				wsp: ADDRESS;				guardindex: INTEGER;				guardno: CARDINAL;				guardcount: CARDINAL;				opened: Channel;				sons: CARDINAL;				msgadr: ADDRESS;				msglen: CARDINAL;			    END;	Queue =	RECORD		    head, tail: ProcessType;		END;	ChannelDescriptor = RECORD				senders: Queue;				owner: ProcessType;				guardindex: INTEGER;				next: Channel;			    END;  VAR	cp: ProcessType;	free, ready: Queue;(* ------------ Private modules and procedures ------------- *)  MODULE ProcessQueue;    IMPORT	ProcessType, Queue;    EXPORT	Push, Pop, InitQueue, IsEmpty;    PROCEDURE InitQueue(VAR q: Queue);    BEGIN	WITH q DO		head := NIL;		tail := NIL	END    END InitQueue;    PROCEDURE Push(p: ProcessType; VAR q: Queue);    BEGIN	p^.next := NIL;	WITH q DO		IF head = NIL THEN			tail := p		ELSE			head^.next := p		END;		head := p	END    END Push;    PROCEDURE Pop(VAR q: Queue; VAR p: ProcessType);    BEGIN	WITH q DO		p := tail;		IF p # NIL THEN			tail := tail^.next;			IF head = p THEN				head := NIL			END		END	END    END Pop;    PROCEDURE IsEmpty(q: Queue): BOOLEAN;    BEGIN	RETURN q.head = NIL    END IsEmpty;  END ProcessQueue;  PROCEDURE DoTransfer;    VAR	aux: ProcessType;  BEGIN	aux := cp;	Pop(ready, cp);	IF cp = NIL THEN		HALT	ELSE		TRANSFER(aux^.cor, cp^.cor)	END  END DoTransfer;  PROCEDURE OpenChannel(ch: Channel; n: INTEGER);  BEGIN	WITH ch^ DO		IF guardindex = 0 THEN			guardindex := n;			next := cp^.opened;			cp^.opened := ch		END	END  END OpenChannel;  PROCEDURE CloseChannels(p: ProcessType);  BEGIN	WITH p^ DO		WHILE opened # NIL DO			opened^.guardindex := 0;			opened := opened^.next		END	END  END CloseChannels;  PROCEDURE ThereAreOpenChannels(): BOOLEAN;  BEGIN	RETURN cp^.opened # NIL;  END ThereAreOpenChannels;  PROCEDURE Sending(ch: Channel): BOOLEAN;  BEGIN	RETURN NOT IsEmpty(ch^.senders)  END Sending;(* -------------- Public Procedures ----------------- *)  PROCEDURE COBEGIN;  (* Beginning of a COBEGIN .. COEND structure *)  BEGIN  END COBEGIN;  PROCEDURE COEND;  (* End of a COBEGIN .. COEND structure *)    (* VAR	aux: ProcessType; *)  BEGIN	IF cp^.sons > 0 THEN		DoTransfer	END  END COEND;  PROCEDURE StartProcess(P: PROC);  (* Start an anonimous process that executes the procedure P *)    VAR newprocess: ProcessType;  BEGIN	Pop(free, newprocess);	IF newprocess = NIL THEN		Allocate(newprocess,SIZE(ProcessDescriptor));		Allocate(newprocess^.wsp, WorkSpaceSize)	END;	WITH newprocess^ DO		father := cp;		sons := 0;		msglen := 0;		NEWPROCESS(P, wsp, WorkSpaceSize, cor)	END;	cp^.sons := cp^.sons + 1;	Push(newprocess, ready)  END StartProcess;  PROCEDURE StopProcess;  (* Terminate a Process (itself) *)    VAR aux: ProcessType;  BEGIN	aux := cp^.father;	aux^.sons := aux^.sons - 1;	IF aux^.sons = 0 THEN		Push(aux, ready)	END;	aux := cp;	Push(aux, free);	Pop(ready, cp);	IF cp = NIL THEN		HALT	ELSE		TRANSFER(aux^.cor, cp^.cor)	END  END StopProcess;  PROCEDURE InitChannel(VAR ch: Channel);  (* Initialize the channel ch *)  BEGIN	Allocate(ch, SIZE(ChannelDescriptor));	WITH ch^ DO		InitQueue(senders);		owner := NIL;		next := NIL;		guardindex := 0	END  END InitChannel;  PROCEDURE GetChannel(ch: Channel);  (* Assign the channel ch to the process that gets it *)  BEGIN	WITH ch^ DO		IF owner # NIL THEN			Message("Channel already has an owner");			HALT		END;		owner := cp	END  END GetChannel;  PROCEDURE Send(data: ARRAY OF BYTE; VAR ch: Channel);  (* Send a message with the data to the cvhannel ch *)    VAR	m: ByteAddress;	(* aux: ProcessType; *)	i: CARDINAL;  BEGIN	WITH ch^ DO		Push(cp, senders);		Allocate(cp^.msgadr, SIZE(data));		m := cp^.msgadr;		cp^.msglen := HIGH(data);		FOR i := 0 TO HIGH(data) DO			m^ := data[i];			m := ADDRESS(m) + 1		END;		IF guardindex # 0 THEN			owner^.guardindex := guardindex;			CloseChannels(owner);			Push(owner, ready)		END	END;	DoTransfer  END Send;  PROCEDURE Receive(VAR ch: Channel; VAR dest: ARRAY OF BYTE);  (* Receive a message from the channel ch into the dest variable *)    VAR	aux: ProcessType;	m: ByteAddress;	i: CARDINAL;  BEGIN	WITH ch^ DO		IF cp # owner THEN			Message("Only owner of channel can receive from it");			HALT		END;		IF Sending(ch) THEN			Pop(senders, aux);			m := aux^.msgadr;			FOR i := 0 TO aux^.msglen DO				dest[i] := m^;				m := ADDRESS(m) + 1			END;			Push(aux, ready);			Push(cp, ready);			CloseChannels(cp)		ELSE			OpenChannel(ch, -1);			DoTransfer;			Pop(senders, aux);			m := aux^.msgadr;			FOR i := 0 TO aux^.msglen DO				dest[i] := m^;				m := ADDRESS(m) + 1			END;			Push(cp, ready);			Push(aux, ready)		END;		Deallocate(aux^.msgadr, aux^.msglen+1);		DoTransfer	END  END Receive;  PROCEDURE SELECT(n: CARDINAL);  (* Beginning of a SELECT structure with n guards *)  BEGIN	cp^.guardindex := Uniform(1,n);	cp^.guardno := n;	cp^.guardcount := n  END SELECT;  PROCEDURE NEXTGUARD(): CARDINAL;  (* Returns an index to the next guard to be evaluated in a SELECT *)  BEGIN	RETURN cp^.guardindex  END NEXTGUARD;  PROCEDURE GUARD(cond: BOOLEAN; ch: Channel;		  VAR dest: ARRAY OF BYTE): BOOLEAN;  (* Evaluates a guard, including reception management *)    (* VAR	aux: ProcessType; *)  BEGIN	IF NOT cond THEN		RETURN FALSE	ELSIF ch = NIL THEN		CloseChannels(cp);		cp^.guardindex := 0;		RETURN TRUE	ELSIF Sending(ch) THEN		Receive(ch, dest);		cp^.guardindex := 0;		RETURN TRUE	ELSE		OpenChannel(ch, cp^.guardindex);		RETURN FALSE	END  END GUARD;  PROCEDURE ENDSELECT(): BOOLEAN;  (* End of a SELECT structure *)  BEGIN	WITH cp^ DO		IF guardindex <= 0 THEN			RETURN TRUE		END;		guardcount := guardcount - 1;		IF guardcount # 0 THEN			guardindex := (guardindex MOD INTEGER(guardno)) + 1		ELSIF ThereAreOpenChannels() THEN			DoTransfer		ELSE			guardindex := 0		END	END;	RETURN FALSE  END ENDSELECT;BEGIN	InitQueue(free);	InitQueue(ready);	Allocate(cp,SIZE(ProcessDescriptor));	WITH cp^ DO		sons := 0;		father := NIL	ENDEND CSP.