parallel_primes.c

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

#define NUM_THREADS 2
#define PRIME_LIMIT ((int)1e9)

unsigned char sieve[PRIME_LIMIT];

void * print_hello(void * arg){
	int thread_id = *(int *)arg;
	printf("%d says \"Hi!\"\n", thread_id);

	return NULL;
}

void * compute_primes(void * arg){
	int thread_id = *(int *)arg;
	int multiple = thread_id * 2 + 3;

	int i;
	while(multiple <= PRIME_LIMIT){
		for(i = 0; i * multiple <= PRIME_LIMIT; i++){
			if(sieve[i * multiple] < 100)
				sieve[i * multiple] += 1;
			/* if(sieve[i * multiple] >= 2){ */
			/* 	break;	 */
			/* } */
		}
		multiple += NUM_THREADS * 2;
	}

	return NULL;
}

int main(void){
	pthread_t threads[NUM_THREADS];
	int thread_ids[NUM_THREADS];

	int i, ret;
	for(i = 0; i < NUM_THREADS; i++){
		thread_ids[i] = i;
		ret = pthread_create(&threads[i], NULL, &compute_primes, &thread_ids[i]);
		if(ret){
			printf("Thread creation failed with error: %d\n", ret);
		}
	}
	for(i = 0; i < NUM_THREADS; i++){
		pthread_join(threads[i], NULL);
	}
	long long int sum = 2;
	int count = 1;
	for(i = 3; i <= PRIME_LIMIT; i+=2){
		if(sieve[i] == 1){
			sum += i;
			count++;
		}
	}

	printf("Sum: %lld\n", sum);
	printf("Count: %d\n", count);

	return 0;
}