Clojure multi-threaded balls program with agents

Question

I wrote a multi-threaded bouncing ball program in clojure. After starting the animation stream, I do

(send-balls) 

to launch streams of bouncing balls. The balls do not move, and this is displayed on the console -

 (#< Agent@5675b3ee FAILED: #< Ref@313d21d6 : {:x 759, :y 629, :x-speed 3, :y-speed 1}>> #< Agent@22cf3539 FAILED: #< Ref@247881db : {:x 794, :y 258, :x-speed 2, :y-speed 3}>> #< Agent@51af4309 FAILED: #< Ref@445ead9d : {:x 831, :y 251, :x-speed 4, :y-speed 2}>>) 

Can someone point out what is going on here?

 (import '(java.awt Color Graphics Dimension) '(java.awt.image BufferedImage) '(javax.swing JPanel JFrame)) (def width 1000) (def height 1000) (def number-of-balls 3) (def rad 20) (def origin-x 100) (def origin-y 100) (def box-height 500) (def box-width 700) (def max-x (+ origin-x box-width (* 4 rad))) (def max-y (+ origin-y box-height (* 4 rad))) (def min-x origin-x) (def min-y origin-y) (defn init-x [] (+ (rand-int (- max-x min-x)) min-x)) (defn init-y [] (+ (rand-int (- max-y min-y)) min-y)) (defstruct ball :x :y :x-speed :y-speed) (def balls (apply vector (map (fn [_] (ref (struct ball (init-x) (init-y) (rand-int 10) (rand-int 10)))) (range number-of-balls)))) (def ball-agents (apply vector (map agent balls))) (defn get-ball [n] (balls n)) (defn set-new-x [ball] (let [x (@ball :x) x-speed (@ball :x-speed) new-x (+ x x-speed)] (dosync (if (and (>= new-x min-x) (<= new-x max-x)) (ref-set ball (assoc @ball :x new-x)) (ref-set ball (assoc @ball :x-speed (* -1 x-speed))))) (println "the new x is " @(ball :x))) @ball) (defn set-new-y [ball] (let [y (@ball :y) y-speed (@ball :y-speed) new-y (+ y y-speed)] (dosync (if (and (>= new-y min-y) (<= new-y max-y)) (ref-set ball (assoc @ball :y new-y)) (ref-set ball (assoc @ball :y-speed (* -1 y-speed)))))) @ball) (defn paint-balls [bg xy] (doto bg (.setColor (. Color red)) (.fillOval xy rad rad))) (defn render [g] (let [img (new BufferedImage width height (. BufferedImage TYPE_INT_ARGB)) bg (. img (getGraphics))] (doto bg (.setColor (. Color white)) (.fillRect 0 0 (. img (getWidth)) (. img (getHeight))) (.setColor (. Color red)) (.drawRect origin-x origin-y (+ origin-x box-width) (+ origin-y box-height))) (dorun (for [i (range number-of-balls)] (do (paint-balls bg (@(get-ball i) :x) (@(get-ball i) :y))))) (. g (drawImage img 0 0 nil)) (. bg (dispose)))) (def panel (doto (proxy [JPanel] [] (paint [g] (render g))) (.setPreferredSize (new Dimension width height)))) (def frame (doto (new JFrame) (.add panel) .pack .show)) (def animator (agent nil)) (defn bounce [x] (while true (set-new-x @*agent*) (set-new-y @*agent*) (. Thread (sleep 100)) (println "here in bounce " *agent*))) (defn animation [x] (send-off *agent* animation) (. panel (repaint)) (. Thread (sleep 100))) (defn send-balls [] (doall (for [i (range number-of-balls)] (do (send-off (ball-agents i) bounce))))) (send-off animator animation) 

Answer 1

As I see the main problem - the functions that you send to the agents do NOT work with the agent, but with its value (ref). By excluding @ in the set-new-x and set-new-y functions, you can make it work.

 (ns balls) (import '(java.awt Color Graphics Dimension) '(java.awt.image BufferedImage) '(javax.swing JPanel JFrame)) (def width 1000) (def height 1000) (def number-of-balls 3) (def rad 20) (def origin-x 100) (def origin-y 100) (def box-height 500) (def box-width 700) (def max-x (+ origin-x box-width (* 4 rad))) (def max-y (+ origin-y box-height (* 4 rad))) (def min-x origin-x) (def min-y origin-y) (defn init-x [] (+ (rand-int (- max-x min-x)) min-x)) (defn init-y [] (+ (rand-int (- max-y min-y)) min-y)) (defstruct ball :x :y :x-speed :y-speed) (def balls (apply vector (map (fn [_] (ref (struct ball (init-x) (init-y) (rand-int 10) (rand-int 10)))) (range number-of-balls)))) (def ball-agents (apply vector (map agent balls))) (defn get-ball [n] (balls n)) (defn set-new-x [ball] (let [x (ball :x) x-speed (ball :x-speed) new-x (+ x x-speed)] (dosync (if (and (>= new-x min-x) (<= new-x max-x)) (alter ball assoc :x new-x) (alter ball assoc :x-speed (* -1 x-speed))))) ball) (defn set-new-y [ball] (let [y (ball :y) y-speed (ball :y-speed) new-y (+ y y-speed)] (dosync (if (and (>= new-y min-y) (<= new-y max-y)) (alter ball assoc :y new-y) (alter ball assoc :y-speed (* -1 y-speed)))) ball)) (defn paint-balls [bg xy] (doto bg (.setColor (. Color red)) (.fillOval xy rad rad))) (defn render [g] (let [img (new BufferedImage width height (. BufferedImage TYPE_INT_ARGB)) bg (. img (getGraphics))] (doto bg (.setColor (. Color white)) (.fillRect 0 0 (. img (getWidth)) (. img (getHeight))) (.setColor (. Color red)) (.drawRect origin-x origin-y (+ origin-x box-width) (+ origin-y box-height))) (dorun (for [i (range number-of-balls)] (do (paint-balls bg (@(get-ball i) :x) (@(get-ball i) :y))))) (. g (drawImage img 0 0 nil)) (. bg (dispose)))) (def panel (doto (proxy [JPanel] [] (paint [g] (render g))) (.setPreferredSize (new Dimension width height)))) (def frame (doto (new JFrame) (.add panel) .pack .show)) (def animator (agent nil)) (defn bounce [ball_cur] (do (Thread/sleep 100) (send-off *agent* bounce) (set-new-x (set-new-y ball_cur)))) (defn animation [x] (send-off *agent* animation) (. panel (repaint)) (. Thread (sleep 100))) (defn send-balls [] (doall (for [i (range number-of-balls)] (do (send-off (ball-agents i) bounce))))) (send-off animator animation) (send-balls) 

Answer 2

I think you do not need links inside agents. See below a working version with simple agents. You can download the code, for example. via load-file , then just type start . The frame will appear with the desired animation. It can be stopped with reset! returned atom to false . You can have, like many independent animation frames, as you wish, triggering a launch more than once.

Hope this helps.

 (import '(java.awt Color Graphics Dimension) '(java.awt.image BufferedImage) '(javax.swing JPanel JFrame)) (def width 1000) (def height 1000) (def number-of-balls 3) (def rad 20) (def origin-x 100) (def origin-y 100) (def box-height 500) (def box-width 700) (def min-borders {:x origin-x :y origin-y}) (def max-borders {:x (+ origin-x box-width (* 4 rad)) :y (+ origin-y box-height (* 4 rad))}) (defn init [coord] (+ (rand-int (- (get max-borders coord) (get min-borders coord))) (get min-borders coord))) (defn init-balls [] (->> (repeatedly number-of-balls #(array-map :x (init :x) :y (init :y) :x-speed (rand-int 10) :y-speed (rand-int 10))) (map agent) vec)) (defn update-coordinate [ball coord-key speed-key] (let [coord (get ball coord-key) speed (get ball speed-key) new-c (+ coord speed)] (if (<= (get min-borders coord-key) new-c (get max-borders coord-key)) (assoc ball coord-key new-c) (assoc ball speed-key (- speed))))) (defn paint-ball [bg xy] (doto bg (.setColor Color/red) (.fillOval xy rad rad))) (defn render [g balls] (let [img (BufferedImage. width height BufferedImage/TYPE_INT_ARGB) bg (.getGraphics img)] (doto bg (.setColor Color/white) (.fillRect 0 0 (.getWidth img) (.getHeight img)) (.setColor Color/red) (.drawRect origin-x origin-y (+ origin-x box-width) (+ origin-y box-height))) (doseq [b balls] (let [ball @b] (paint-ball bg (:x ball) (:y ball)))) (.drawImage g img 0 0 nil))) (defn bounce [ball running?] (when @running? (send-off *agent* bounce running?)) (Thread/sleep 100) (-> ball (update-coordinate :x :x-speed) (update-coordinate :y :y-speed))) (defn animation [panel running?] (while @running? (javax.swing.SwingUtilities/invokeAndWait #(.repaint panel)) (Thread/sleep 100))) (defn start [] (let [running? (atom true) balls (init-balls) panel (doto (proxy [JPanel] [] (paint [g] (render g balls))) (.setPreferredSize (Dimension. width height))) frame (doto (JFrame.) (.add panel) .pack .show)] (doseq [b balls] (send-off b bounce running?)) (future (animation panel running?)) running?)) 

Answer 3

The send (or send) function (in this case: bounce) should return the (new) state of the agents. This is fully described here .

Answer 4

There are a couple of code issues -

• As Maurits noted, a rebound does not return a new agent state.
• There is no place in the bounce function where a rebound is added to the agent action queue again. This is necessary because the new coordinated need must be calculated again and again.