(in-package :locked-queue)

(declaim (optimize (space 0) (speed 0) (safety 3) (debug 3)))

(defclass locked-queue ()
  ((queue :initform nil)
   (mutex :initform (sb-thread:make-mutex :name "queue lock"))
   (waitq :initform (make-waitqueue))))

(defun create ()
  (make-instance 'locked-queue))

(defmethod dequeue ((q locked-queue))
  (with-slots (queue mutex waitq) q
    (with-mutex (mutex)
      (if (or (null queue)
	      (null (first queue)))
	  (condition-wait waitq mutex))
      (prog1 (first (car queue))
	(setf (car queue)
	      (rest (car queue)))))))

(defmethod enqueue ((q locked-queue) value)
  (with-slots (queue mutex waitq) q
    (with-mutex (mutex)
      (let ((last (list value)))
	(if (null (first queue))
	    (progn
	      (setf queue (cons last last))
	      (condition-notify waitq))
	    (progn
	      (setf (rest (cdr queue))
		    last
		    (cdr queue) last)
	      (cons (car queue) last)))))))