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