Distributed Monte Carlo estimation of pi using posix message queue

pi.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>
#include <math.h>
#include <mqueue.h>
#include <sys/stat.h>
#include <errno.h>

#define RADIUS 1000
#define QNAME "/piqueue"

int is_in_circle(double x, double y, double radius) {
	return x * x + y * y < radius * radius;
}

double test_pi (int iters){
	int in_circle = 0;
	double x, y;
	for (int i = 0; i < iters; ++i){
		x = (rand() % (2 * RADIUS)) - RADIUS,
		y = (rand() % (2 * RADIUS)) - RADIUS;
		if (is_in_circle(x, y, RADIUS)){
			in_circle++;
		}
	}
	return 4 * (in_circle / (double) iters);

}

int main(int argc, char** argv){
		if (argc < 2){
			printf("expected args: proc, iters\n");
			exit(1);
		}
		int proc = atoi(argv[1]),
			iters = atoi(argv[2]);
		struct mq_attr attr;
		mqd_t msgq_id;
		attr.mq_maxmsg = 300;
		attr.mq_msgsize = sizeof(double);
		msgq_id = mq_open(QNAME, O_RDWR | O_CREAT, 644, &attr);
		mq_unlink(QNAME);
		for (int i = 0; i < proc; ++i){
			if (!fork()){
				srand(time(0) * getpid());
				double pi = test_pi(iters);
				mq_send(msgq_id, &pi, sizeof(double), 1);
				exit(0);
			}
		}	
		int status, prio;
		double sum = 0.0, result;
		for (int i = 0; i < proc; ++i){
			wait(&status);
			mq_receive(msgq_id, &result, sizeof(double), &prio);
			sum += result;
		}
		printf("%f\n", sum / proc);
		exit(0);
}