Data commit

Task/Atomic-updates/Scala/atomic-updates.scala

@@ -0,0 +1,75 @@
+object AtomicUpdates {
+
+  class Buckets(ns: Int*) {
+
+    import scala.actors.Actor._
+
+    val buckets = ns.toArray
+
+    case class Get(index: Int)
+    case class Transfer(fromIndex: Int, toIndex: Int, amount: Int)
+    case object GetAll
+
+    val handler = actor {
+      loop {
+        react {
+          case Get(index) => reply(buckets(index))
+          case Transfer(fromIndex, toIndex, amount) =>
+            assert(amount >= 0)
+            val actualAmount = Math.min(amount, buckets(fromIndex))
+            buckets(fromIndex) -= actualAmount
+            buckets(toIndex) += actualAmount
+          case GetAll => reply(buckets.toList)
+        }
+      }
+    }
+
+    def get(index: Int): Int = (handler !? Get(index)).asInstanceOf[Int]
+    def transfer(fromIndex: Int, toIndex: Int, amount: Int) = handler ! Transfer(fromIndex, toIndex, amount)
+    def getAll: List[Int] = (handler !? GetAll).asInstanceOf[List[Int]]
+  }
+
+  def randomPair(n: Int): (Int, Int) = {
+    import scala.util.Random._
+    val pair = (nextInt(n), nextInt(n))
+    if (pair._1 == pair._2) randomPair(n) else pair
+  }
+
+  def main(args: Array[String]) {
+    import scala.actors.Scheduler._
+    val buckets = new Buckets(List.range(1, 11): _*)
+    val stop = new java.util.concurrent.atomic.AtomicBoolean(false)
+    val latch = new java.util.concurrent.CountDownLatch(3)
+    execute {
+      while (!stop.get) {
+        val (i1, i2) = randomPair(10)
+        val (n1, n2) = (buckets.get(i1), buckets.get(i2))
+        val m = (n1 + n2) / 2
+        if (n1 < n2)
+          buckets.transfer(i2, i1, n2 - m)
+        else
+          buckets.transfer(i1, i2, n1 - m)
+      }
+      latch.countDown
+    }
+    execute {
+      while (!stop.get) {
+        val (i1, i2) = randomPair(10)
+        val n = buckets.get(i1)
+        buckets.transfer(i1, i2, if (n == 0) 0 else scala.util.Random.nextInt(n))
+      }
+      latch.countDown
+    }
+    execute {
+      for (i <- 1 to 20) {
+        val all = buckets.getAll
+        println(all.sum + ":" + all)
+        Thread.sleep(500)
+      }
+      stop.set(true)
+      latch.countDown
+    }
+    latch.await
+    shutdown
+  }
+}