90 lines
2.4 KiB
Java
90 lines
2.4 KiB
Java
import java.util.Scanner;
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import java.util.Random;
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public class CheckpointSync{
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public static void main(String[] args){
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System.out.print("Enter number of workers to use: ");
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Scanner in = new Scanner(System.in);
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Worker.nWorkers = in.nextInt();
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System.out.print("Enter number of tasks to complete:");
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runTasks(in.nextInt());
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}
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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 static void runTasks(int nTasks){
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for(int i = 0; i < nTasks; i++){
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System.out.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 static void runThreads(){
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for(int i = 0; i < Worker.nWorkers; i ++){
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new Thread(new Worker(i+1)).start();
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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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public static class Worker implements Runnable{
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public Worker(int threadID){
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this.threadID = threadID;
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}
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public void run(){
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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 synchronized void work(){
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try {
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int workTime = rgen.nextInt(900) + 100;
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System.out.println("Worker " + threadID + " will work for " + workTime + " msec.");
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Thread.sleep(workTime); //work for 'workTime'
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nFinished++; //increases work finished counter
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System.out.println("Worker " + threadID + " is ready");
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} catch (InterruptedException e) {
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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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* 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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public static synchronized void checkpoint(){
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while(nFinished != nWorkers){
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try {
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Thread.sleep(10);
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} catch (InterruptedException e) {
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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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nFinished = 0;
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}
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/* inner class instance variables */
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private int threadID;
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/* static variables */
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private static Random rgen = new Random();
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private static int nFinished = 0;
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public static int nWorkers = 0;
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}
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}
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