parallelComputing.c

#include <sys/times.h>
#include <time.h>
#include <stdio.h> 
#include <pthread.h> 



struct timespec tpBegin1,tpEnd1,tpBegin2,tpEnd2,tpBegin3,tpEnd3;  //These are inbuilt structures to store the time related activities

double compute(struct timespec start,struct timespec end) //computes time in milliseconds given endTime and startTime timespec structures.
{
  double t;
  t=(end.tv_sec-start.tv_sec)*1000;
  t+=(end.tv_nsec-start.tv_nsec)*0.000001;

  return t;
}

int array[100];

void *expensive_function(void *param) {     
  int   index = *((int*)param);
  int   i;
  for (i = 0; i < 100000000; i++)
    array[index]+=1;
} 

int main(int argc, char *argv[]) { 
  int       first_elem  = 0;
  int       bad_elem    = 1;
  int       good_elem   = 99;
  double time1;
  double time2;
  double time3;
  pthread_t     thread_1;
  pthread_t     thread_2;

  //---------------------------START--------Serial Computation---------------------------------------------

  clock_gettime(CLOCK_REALTIME,&tpBegin1);
  expensive_function((void*)&first_elem);
  expensive_function((void*)&bad_elem);
  clock_gettime(CLOCK_REALTIME,&tpEnd1);

  //---------------------------END----------Serial Computation---------------------------------------------


  //---------------------------START--------parallel computation with False Sharing----------------------------

  clock_gettime(CLOCK_REALTIME,&tpBegin2);
  pthread_create(&thread_1, NULL,expensive_function, (void*)&first_elem);
  pthread_create(&thread_2, NULL,expensive_function, (void*)&bad_elem);
  pthread_join(thread_1, NULL);
  pthread_join(thread_2, NULL);
  clock_gettime(CLOCK_REALTIME,&tpEnd2);

  //---------------------------END----------parallel computation with False Sharing----------------------------


  //---------------------------START--------parallel computation without False Sharing------------------------

  clock_gettime(CLOCK_REALTIME,&tpBegin3);   
  pthread_create(&thread_1, NULL,expensive_function, (void*)&first_elem);
  pthread_create(&thread_2, NULL,expensive_function, (void*)&good_elem);
  pthread_join(thread_1, NULL);
  pthread_join(thread_2, NULL);
  clock_gettime(CLOCK_REALTIME,&tpEnd3);

  //---------------------------END--------parallel computation without False Sharing------------------------


  //--------------------------START------------------OUTPUT STATS--------------------------------------------
  printf("array[first_element]: %d\t\t array[bad_element]: %d\t\t array[good_element]: %d\n\n\n", array[first_elem],array[bad_elem],array[good_elem]);


  time1 = compute(tpBegin1,tpEnd1);
  time2 = compute(tpBegin2,tpEnd2);
  time3 = compute(tpBegin3,tpEnd3);
  printf("Time take with false sharing      : %f ms\n", time2);
  printf("Time taken without false sharing  : %f ms\n", time3);
  printf("Time taken in Sequential computing : %f ms\n", time1);

  //--------------------------END------------------OUTPUT STATS--------------------------------------------
  

  return 0; 
}