pth_monte_carlo_pi.c, C (gcc)

pth_monte_carlo_pi.c

//gcc 7.4.0

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

int thread_count;
pthread_mutex_t mutex;
unsigned long long number_of_tosses;
unsigned long long number_in_circle;

void* Monte_Carlo(void* rank);

int main(void)
{
    struct timeval t;
    double start, finish, pi_estimate;
    long thread;
    pthread_t* thread_handles;
    
    //thread_count = strtol(argv[1], NULL, 10);
    thread_count = 2;
    
    printf("Enter the number of tosses:\n");
    scanf("%llu", &number_of_tosses);
    number_in_circle = 0;
    
    pthread_mutex_init(&mutex, NULL);
    thread_handles = malloc(thread_count * sizeof(pthread_t));
    
    gettimeofday(&t, NULL);
    start = t.tv_sec + t.tv_usec / 1000000.0;
    
    for(thread = 0; thread < thread_count; thread++)
    {
        pthread_create(&thread_handles[thread], NULL,
                       Monte_Carlo, (void*) thread);
    }
    
    for(thread = 0; thread < thread_count; thread++)
    {
        pthread_join(thread_handles[thread], NULL);
    }
    
    pi_estimate =  4 * number_in_circle / ((double) number_of_tosses);
    
    gettimeofday(&t, NULL);
    finish = t.tv_sec + t.tv_usec / 1000000.0;
    
    
    printf("Number in circle: %llu\n", number_in_circle);
    printf("Number of tosses: %llu\n", number_of_tosses);
    printf("The estimate of pi = %lf\n", pi_estimate);
    printf("The elapsed time = %e ms\n", (finish - start) * 1000);
    
    pthread_mutex_destroy(&mutex);
    free(thread_handles);
    return 0;
}

void* Monte_Carlo(void* rank)
{
    double x, y, distance_squared;
    long my_rank = (long) rank;
    unsigned long long toss;
    unsigned long long my_number_of_tosses = number_of_tosses / thread_count;
    unsigned long long my_number_in_circle = 0;
    
    for(toss = 0; toss < my_number_of_tosses; toss++)
    {
        x = ((double) rand_r(&my_rank)) / RAND_MAX * 2.0 - 1.0;
        y = ((double) rand_r(&my_rank)) / RAND_MAX * 2.0 - 1.0;
        distance_squared = x * x + y * y;
        if(distance_squared <= 1)
        {
            my_number_in_circle++;
        }
    }
    
    pthread_mutex_lock(&mutex);
    number_in_circle += my_number_in_circle;
    pthread_mutex_unlock(&mutex);
    
    return NULL;
}


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