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

long int MAX;
long int sum = 0;
long int n_threads;
pthread_mutex_t lock;

void* somador(void *tid){
	long int i, start, end, sum_local = 0;
	long int *id = (long int *) tid;

	start = *id * (MAX / n_threads);
	if(*id == n_threads - 1)
		end = MAX;
	else
		end = start + (MAX / n_threads);
	
	for(i = start; i < end; i++)
		sum_local++;

	printf("thread %ld - sum = %ld\n", *id, sum_local);

    pthread_mutex_lock(&lock);
    sum += sum_local;
    pthread_mutex_unlock(&lock);


	pthread_exit(NULL);
}

int main(int argc, char ** argv) {
	if(argc != 3){
		fprintf(stderr, "Usage: %s <n_threads> <max>\n", argv[0]);
		exit(EXIT_FAILURE);
	}
	n_threads = atoi(argv[1]);
	MAX = atoi(argv[2]);

	long int tid;
	pthread_t *threads;
	struct timespec start, finish;
	double elapsed;

	threads = (pthread_t *) malloc(n_threads * sizeof(pthread_t));

	pthread_mutex_init(&lock, NULL);

	clock_gettime(CLOCK_MONOTONIC, &start);

	for(tid = 0; tid < n_threads; tid++)
		pthread_create(&threads[tid], NULL, (void *) somador, (void *) &tid);

	for(tid = 0; tid < n_threads; tid++)
		pthread_join(threads[tid], NULL);

	pthread_mutex_destroy(&lock);
	
	clock_gettime(CLOCK_MONOTONIC, &finish);
	elapsed = (finish.tv_sec - start.tv_sec) + (finish.tv_nsec - start.tv_nsec) / 1000000000.0;

	printf("\nTotal time: %.10f seconds\n\n", elapsed);

	printf("sum global = %ld\n", sum);

	free(threads);

	pthread_exit(NULL);
}