/*
 * ISA 563, Spring 2011
 * Copyleft by Muhammad Abdulla
 */


#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

/*
 * fork-vs-thread.c -- demonstrate speed differences in process and thread creation
 */

#define MAX 20000

void fork_task()
{
   exit(0);
}

void *thread_task(void *data)
{
   pthread_exit(NULL);
}

void forks()
{
   int i;
   int s;
   pid_t pid;

   for ( i = 0; i < MAX; i++ ) {
      if ( (pid = fork()) < 0 ) {
         fprintf(stderr, "fork error.\n");
         exit(-1);
      } else if ( pid == 0 ) { // inside child
         fork_task(); 
      } else {
         waitpid(pid, &s, 0);
      }
   }
}

void threads()
{
   int i, j, retval;
   pthread_t tid;
   pthread_attr_t attr;

   pthread_attr_init(&attr);
   pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

   for ( i = 0; i < MAX; i++ ) {
      // create threads
      retval = pthread_create(&tid, &attr, thread_task, NULL);
      if (retval) {
         printf("Error from pthread_create(). Return value is %d\n", retval);
         exit(-1);
      }

      // wait for thread to finish
      retval = pthread_join(tid, NULL);
      if (retval) {
         printf("Error from pthread_join(). Return value is %d\n", retval);
         exit(-1);
      }
   }
}
   
// return time passed in milli-seconds
double tp (struct timeval start, struct timeval end)
{
   double t;
   t = 1000 * (end.tv_sec - start.tv_sec) + (end.tv_usec - start.tv_usec) / 1000.0;
   return t;
}

int main ( int argc, char *argv[] )
{
   struct timeval tv1;
   struct timeval tv2;

   // measure forking times
   gettimeofday(&tv1, NULL);
   forks();
   gettimeofday(&tv2, NULL);
   printf ( "time to fork %d times: %g (ms)\n", MAX, tp(tv1, tv2) );

   // measure thread creation times
   gettimeofday(&tv1, NULL);
   threads();
   gettimeofday(&tv2, NULL);
   printf ( "time to create threads %d times: %g (ms)\n", MAX, tp(tv1, tv2) );
}