Data commit

Task/Checkpoint-synchronization/Scala/checkpoint-synchronization.scala

@@ -0,0 +1,84 @@
+import java.util.{Random, Scanner}
+
+object CheckpointSync extends App {
+  val in = new Scanner(System.in)
+
+  /*
+   * Informs that workers started working on the task and
+   * starts running threads. Prior to proceeding with next
+   * task syncs using static Worker.checkpoint() method.
+   */
+  private def runTasks(nTasks: Int): Unit = {
+
+    for (i <- 0 until nTasks) {
+      println("Starting task number " + (i + 1) + ".")
+      runThreads()
+      Worker.checkpoint()
+    }
+  }
+
+  /*
+   * Creates a thread for each worker and runs it.
+   */
+  private def runThreads(): Unit =
+    for (i <- 0 until Worker.nWorkers) new Thread(new Worker(i + 1)).start()
+
+  class Worker(/* inner class instance variables */ var threadID: Int)
+    extends Runnable {
+    override def run(): Unit = {
+      work()
+    }
+
+    /*
+     *  Notifies that thread started running for 100 to 1000 msec.
+     *  Once finished increments static counter 'nFinished'
+     *  that counts number of workers finished their work.
+     */
+    private def work(): Unit = {
+      try {
+        val workTime = Worker.rgen.nextInt(900) + 100
+        println("Worker " + threadID + " will work for " + workTime + " msec.")
+        Thread.sleep(workTime) //work for 'workTime'
+
+        Worker.nFinished += 1 //increases work finished counter
+
+        println("Worker " + threadID + " is ready")
+      } catch {
+        case e: InterruptedException =>
+          System.err.println("Error: thread execution interrupted")
+          e.printStackTrace()
+      }
+    }
+  }
+
+  /*
+   * Worker inner static class.
+   */
+  object Worker {
+    private val rgen = new Random
+    var nWorkers = 0
+    private var nFinished = 0
+
+    /*
+     * Used to synchronize Worker threads using 'nFinished' static integer.
+     * Waits (with step of 10 msec) until 'nFinished' equals to 'nWorkers'.
+     * Once they are equal resets 'nFinished' counter.
+     */
+    def checkpoint(): Unit = {
+      while (nFinished != nWorkers)
+        try Thread.sleep(10)
+        catch {
+          case e: InterruptedException =>
+            System.err.println("Error: thread execution interrupted")
+            e.printStackTrace()
+        }
+      nFinished = 0
+    }
+  }
+
+  print("Enter number of workers to use: ")
+  Worker.nWorkers = in.nextInt
+  print("Enter number of tasks to complete:")
+  runTasks(in.nextInt)
+
+}