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@igor-shevchenko igor-shevchenko/pi.c
Created Oct 31, 2013

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Distributed Monte Carlo estimation of pi using posix message queue
#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);
}
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