source: branches/home/psmith/restructure/src/utils/concurrent-queue.lisp

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(in-package :nio-utils)

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

;Implements a threadsafe queue where readers wait for elements of a FIFO queue to appear using a waitqueue
;Modified from sbcl manual example


(defclass concurrent-queue()
  ((buffer-queue :initform (sb-thread:make-waitqueue)
                 :reader buffer-queue)
;   (buffer-queue-mutex :initform (sb-thread:make-mutex :name "buffer queue mutex")
;                      :reader buffer-queue-mutex)
   (buffer-lock :initform (sb-thread:make-mutex :name "buffer lock")
                :reader buffer-lock)
   (buffer :initform nil
           :accessor buffer)))

(defun concurrent-queue()
  (make-instance 'concurrent-queue))


;Do an (optionally blocking) remove of the element at the head of this queue
(defmethod take ((queue concurrent-queue) &key (blocking-call t))
#+nio-debug (format-log t "concurent-queue:take - (~A) attempting to obtain mutex ~A~%" sb-thread:*current-thread* (buffer-lock queue))
  (sb-thread:with-mutex ((buffer-lock queue))
#+nio-debug (format-log t "concurent-queue:take - (~A) aquired mutex mutex ~A~%" sb-thread:*current-thread* (buffer-lock queue))
    ;if its there, pop it
      (if (> (length (buffer queue)) 0)
          (pop (buffer queue))
          (when blocking-call
            (loop
#+nio-debug (format-log t "concurent-queue:take - (~A) about to wait on queue~%" sb-thread:*current-thread*)
               (sb-thread:condition-wait (buffer-queue queue) (buffer-lock queue))
#+nio-debug (format-log t "concurent-queue:take - (~A) notified on queue~%" sb-thread:*current-thread*)
               (if (> (length (buffer queue)) 0)
                 (return-from take (pop (buffer queue)))))))))

;Append the element to the tail of this queue
(defmethod add ((queue concurrent-queue) elt)
#+nio-debug (format-log t "concurent-queue:add - (~A) adding ~A to ~A~%" sb-thread:*current-thread* elt queue)
  (sb-thread:with-mutex ((buffer-lock queue))
    (setf (buffer queue) (append (buffer queue) (list elt)) )
    (sb-thread:condition-notify (buffer-queue queue))))


(defun test-writer(queue)
  (loop for i from 0 to 100 do
;       (sleep (random 0.1))
       (format-log t "Adding ~A~%" i)
       (add queue i)))
       
(defun test-reader(queue results)
  (format-log t "Started reader ~A~%" sb-thread:*current-thread*)
  (loop
     (let ((elt (take queue)))
       (push elt results)
       (format-log t "reader on ~A got elt ~A~%" 
               sb-thread:*current-thread* 
               results))))

(defparameter *results1* (list 999999))
(defparameter *results2* (list 888888))

(defun test-queue()
  (let ((queue (make-instance 'concurrent-queue)))
    (sb-thread:make-thread #'(lambda()(test-writer queue)))
;    (sleep 10)
    (let ((t1 (sb-thread:make-thread #'(lambda()(test-reader queue *results1*)))))
          ;(t2 (sb-thread:make-thread #'(lambda()(test-reader queue *results2*)))))
      (sleep 5) ;;wait for it to probably complete
      (format-log t "t1 got: ~A~%" *results1*)
      (format-log t "t2 got: ~A~%" *results2*)
      (sb-thread:destroy-thread t1)
;      (sb-thread:destroy-thread t2)
)
    (sb-thread:with-mutex ((buffer-lock queue))
      (assert (eql (length (buffer queue)) 0)))))

(defun test-queue2()
  (let ((queue (make-instance 'concurrent-queue)))
    (sb-thread:make-thread #'(lambda()(test-reader queue)))
    (sb-thread:make-thread #'(lambda()(test-writer queue)))
    (sb-thread:make-thread #'(lambda()(test-reader queue)))
    (sb-thread:make-thread #'(lambda()(test-writer queue)))
    (sleep 10)
    (format-log t "running asserts")
    (sb-thread:with-mutex ((buffer-lock queue))
      (assert (eql (length (buffer queue)) 0)))))