[Speed-up Multi-thread version] pi_multi-thread.c

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

const int NUM_THREADS = 4;

 clock_t start, end;

_Thread_local unsigned int seed = 0;

static int count = 0;

void* circle_cnt(void* loopTimes)
{   int times = 0;
    int loop = (int)loopTimes;

     for(int i=0;i<loop;i++)
    {
        int random_num = rand_r(&seed);
        double x=(double)random_num/((double)RAND_MAX);

        random_num = rand_r(&seed);
        double y=(double)random_num/((double)RAND_MAX);

        double distance= 1.0*x*x + 1.0*y*y;

        if(distance <= 1) times++;
    }
    count = count + times;
    pthread_exit(NULL);
}
int main(int argc, char*argv[])
{
        pthread_t tid[NUM_THREADS];
    int n=atoi(argv[1]);
    int div = n/NUM_THREADS;
    double pi = 1.0;
    srand(time(NULL));
    start = clock();
    int i = 0;
    for (i = 0; i < NUM_THREADS; ++i)
    {
        //pthread_attr_t attr;
        //pthread_attr_init(&attr);
        pthread_create(&tid[i], NULL, circle_cnt, (void*) div);
    }
    for (i = 0; i < NUM_THREADS; ++i)
    {
        pthread_join(tid[i], NULL);
    }
    pi=4.0*count/n;
        end = clock();
        double exe_time = ((double)(end - start)) / ( (double)(CLOCKS_PER_SEC) );
    printf("Pi: %lf\n",pi);
        printf("Time: %g seconds", exe_time);

    return 0;
}