circular.def

DEFINITION MODULE CircularBuffers;

	(****************************************************************)
	(*								*)
	(*	Circular Buffer for passing character data		*)
	(*		between a pair of tasks.			*)
	(*								*)
	(*	Author:		P. Moylan				*)
	(*	Last edited:	7 December 1993				*)
	(*								*)
	(*	Status:		OK.					*)
	(*								*)
	(****************************************************************)

TYPE CircularBuffer;	(* is private *)

PROCEDURE CreateBuffer (VAR (*OUT*) B: CircularBuffer;  size: CARDINAL);

    (* Allocates space for a circular buffer, and initializes it.  The	*)
    (* caller specifies how many characters the buffer will hold.	*)

PROCEDURE PutBuffer (B: CircularBuffer; item: CHAR);

    (* Waits for space available, then puts item at the tail of the queue. *)

PROCEDURE PutBufferImpatient (B: CircularBuffer;  item: CHAR;
						TimeLimit: CARDINAL);

    (* Like PutBuffer, but waits no longer than TimeLimit milliseconds	*)
    (* for a buffer slot to become available.  If the time limit	*)
    (* expires, the oldest item in the buffer is overwritten by the	*)
    (* new data.							*)

PROCEDURE GetBuffer (B: CircularBuffer) : CHAR;

    (* Takes one character from the head of the queue, waiting if necessary. *)

PROCEDURE BufferEmpty (B: CircularBuffer): BOOLEAN;

    (* Returns TRUE iff the buffer is empty. *)

END CircularBuffers.