monte-carlo-os2.c

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

#define NUMTHRDS 4
#define N 100000000
pthread_mutex_t mutex;

double globalUnutra;

void *BusyWork(void*arg)
{
    long tid = (long)arg;

    int i;
    double x, y;
    double unutra = 0.0;
    for (i=tid*N/NUMTHRDS; i<(tid*N/NUMTHRDS)+N/NUMTHRDS; i++)
    {
        x = rand() * 1.0 / RAND_MAX;
        y = rand() * 1.0 / RAND_MAX;
        if((x*x + y*y) <= 1.0)
         unutra++;
    }

    pthread_mutex_lock(&mutex);
    globalUnutra += unutra;
    pthread_mutex_unlock(&mutex);
}

int main()
{
    srand(time(NULL));

    clock_t cStart = clock();

    pthread_t thread[NUMTHRDS];

    long t;
    void *status;
    int rc;

    pthread_mutex_init(&mutex, NULL);

    for(t=0; t<NUMTHRDS; t++)
    {
        rc = pthread_create(&thread[t], NULL, BusyWork, (void *)t);
        if (rc)
        {
          printf("ERROR; return code from pthread_create() is %d\n", rc);
          exit(-1);
        }
    }

    for(t=0; t<NUMTHRDS; t++)
    {
       rc = pthread_join(thread[t], &status);
       if (rc)
       {
          printf("ERROR; return code from pthread_join() is %d\n", rc);
          exit(-1);
        }
    }

    double pi = 0.0;
    pi = 4.0 * (globalUnutra * 1.0 / N);

    clock_t cEnd = clock();

    printf("PI = %lf, potrebno vreme: %lf\n", pi, (cEnd-cStart) * 1.0 / CLOCKS_PER_SEC);

    pthread_mutex_destroy(&mutex);
    pthread_exit(NULL);
}