Modify and run the program shown below in the following way. There is an array o

Question

Modify and run the program shown below in the following way. There is an array of 20 elements defined in the program. The elements of the array are: [20 18 16 14 12 10 8 6 4 2 -10 -20 -30 -40 15 23 25 75 45 33]. Thread 1 adds the first five elements (i.e., 20, 18, 16, 14, 12), Thread 2 adds the next five elements (i.e., 10, 8, 6, 4, 2), Thread 4 adds the last five elements (23, 25, 75, 45, 33). Finally, the sum of all the 20 elements is printed by the program. include #include include #define NUM_THREADS 3 int counter=1; void *PrintHello(void *threadid) {counter = 2*counter+ (int) threadid; printf(" Thread Id: %d Counter: %d ", threadid, counter); pthread_exit(NULL);} int main(int arge, char *argv[]) {pthread_t threads[NUM_THREADS]; int rc, t; for(t=0;t

Explanation / Answer

The modified code is as follows:

1. Include unistd.h (for using sleep function) as follows:

#include<unistd.h>

2.Add global array declaration and a global varaible integer N and modify NUM_THREADS as 4 as follows:

#define NUM_THREADS 4
int counter=1;
int array[20];
int N = 0;

3. PrintHello function will be modified as follows:

void *PrintHello(void *threadid)
{
   counter = 2*counter+(int)threadid;
   printf (" Thread Id:%d Counter: %d ",threadid,counter);

   /*-------------------Modified Code-------------------*/
   if (N == 0)){
      for (int i = N; i<N + 5; i++){
         array[i] = 20 - 2 * i;     
      }
      N = 5; // Value is set so that the next thread can fill from N = 5 onwards
   }
   else {
      if (N == 5)){
         for (int i = N; i<N + 5; i++){
            array[i] = 10 - 2 * (i - N);     
         }
         N = 10; Value is set so that the next thread can fill from N = 10 onwards
      }
      else {
         if (N == 10)){
            for (int i = N; i<N + 4; i++){
               array[i] = -10 - 10 * (i - N);     
            }
            array[N+4] = 15;
            N = 15; //Value is set so that the next thread can fill from N = 15 onwards
         }
         else {
             if (N == 15)){
                 array[N] = 23;
                 array[N +1] = 25;
                 array[N + 2] - 75;
                 array[N + 3] - 45;
                 array[N + 3] - 33;

              }           
           }

         }
      }
   }
}

4. Main code is modified as follows:

   int main(int argc, char *argv[])
   {
      pthread_t threads[NUM_THREADS];
      int rc,t;
      int sum = 0;

      /*-----------------Modified Cosde--------------------*/

      for (t=0; t<NUM_THREADS; t++){
          printf("Creating thread %d ",t);
          rc = pthread_create(&threads[t],NULL,PrintHello, (void *)t);
          if (rc) {
             printf("ERROR:return code for pthread_create is %d ",rc);
             exit(-1)
          }
          sleep(2); //This sleep is added so that the created thread gets enough time to fill the array.
      }
      printf(" Counter: %d ,counter);
      for (int i = 0; i<20; i++)
          sum = sum + array[i];

      printf("Sum is %d ",sum);
      pthread_exit(NULL)
   }

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