Question

Write an application that uses parallelism to compute the sum of the integers in an array of size 100000. You can populate the array with random numbers and your application should display the sum.

Answer 1

Java Program for the aboveproblem statement :-

The Below program will generate the sum of 100000 random numbers both in SIngle summation and using Parallelism.

import java.util.Random;

class Summation extends Thread {

   private int[] arr;

   private int low, high;
   private long partial;

   public Summation(int[] arr, int low, int high) {
       this.arr = arr;
       this.low = low;
       this.high = Math.min(high, arr.length);
   }

   public long getPartialSum() {
       return partial;
   }

   public void run() {
       partial = sum(arr, low, high);
   }

   public static long sum(int[] arr) {
       return sum(arr, 0, arr.length);
   }

   public static long sum(int[] arr, int low, int high) {
       long total = 0;

       for (int i = low; i < high; i++) {
           total += arr[i];
       }

       return total;
   }

   public static long parallelSum(int[] arr) {
       return parallelSum(arr, Runtime.getRuntime().availableProcessors());
   }

   public static long parallelSum(int[] arr, int threads) {
       int size = (int) Math.ceil(arr.length * 1.0 / threads);

       Summation[] sums = new Summation[threads];

       for (int i = 0; i < threads; i++) {
           sums[i] = new Summation(arr, i * size, (i + 1) * size);
           sums[i].start();
       }

       try {
           for (Summation sum : sums) {
               sum.join();
           }
       } catch (InterruptedException e) {
       }

       int total = 0;

       for (Summation sum : sums) {
           total += sum.getPartialSum();
       }

       return total;
   }

   public static void main(String[] args) {
       Random rand = new Random();

       int[] arr = new int[100000];

       for (int i = 0; i < arr.length; i++) {
           arr[i] = rand.nextInt(101) + 1; // 1..100
      
       }

       long start = System.currentTimeMillis();

       System.out.println("single summantion value is :- " + Summation.sum(arr));

       System.out.println("Single: " + (System.currentTimeMillis() - start)); // Single:
                                                                               // 44

       start = System.currentTimeMillis();

          System.out.println("parallel summantion value is :- " + Summation.parallelSum(arr));

       System.out.println("Parallel: " + (System.currentTimeMillis() - start)); // Parallel:
                                                                                   // 25
   }

}