Data commit

Task/Atomic-updates/Clojure/atomic-updates-1.clj

@@ -0,0 +1,7 @@
+(defn xfer [m from to amt]
+  (let [{f-bal from t-bal to} m
+        f-bal (- f-bal amt)
+        t-bal (+ t-bal amt)]
+    (if (or (neg? f-bal) (neg? t-bal))
+      (throw (IllegalArgumentException. "Call results in negative balance."))
+      (assoc m from f-bal to t-bal))))

Task/Atomic-updates/Clojure/atomic-updates-2.clj

@@ -0,0 +1,2 @@
+(def *data* (atom {:a 100 :b 100})) ;; *data* is an atom holding a map
+(swap! *data* xfer :a :b 50) ;; atomically results in *data* holding {:a 50 :b 150}

Task/Atomic-updates/Clojure/atomic-updates-3.clj

@@ -0,0 +1,22 @@
+(defn equalize [m a b]
+  (let [{a-val a b-val b} m
+        diff (- a-val b-val)
+        amt (/ diff 2)]
+    (xfer m a b amt)))
+
+(defn randomize [m a b]
+  (let [{a-val a b-val b} m
+        min-val (min a-val b-val)
+        amt (rand-int (- min-val) min-val)]
+    (xfer m a b amt)))
+
+(defn test-conc [f data a b n name]
+  (dotimes [i n]
+    (swap! data f a b)
+    (println (str "total is " (reduce + (vals @data)) " after " name " iteration " i))))
+
+(def thread-eq (Thread. #(test-conc equalize *data* :a :b 1000 "equalize")))
+(def thread-rand (Thread. #(test-conc randomize *data* :a :b 1000 "randomize")))
+
+(.start thread-eq)
+(.start thread-rand)