slide 11 of 19

Compute Pi Using bb_threads

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include "bb_threads.h"

volatile double pi = 0.0;
volatile int intervals;
volatile int pids[2];      /* Unix PIDs of threads */

void
do_pi(void *data,
size_t len)
{
  register double width, localsum;
  register int i;
  register int iproc = (getpid() != pids[0]);

  /* set width */
  width = 1.0 / intervals;

  /* do the local computations */
  localsum = 0;
  for (i=iproc; i<intervals; i+=2) {
    register double x = (i + 0.5) * width;
    localsum += 4.0 / (1.0 + x * x);
  }
  localsum *= width;

  /* get permission, update pi, and unlock */
  bb_threads_lock(0);
  pi += localsum;
  bb_threads_unlock(0);
}

int
main(int argc,
char **argv)
{
  /* get the number of intervals */
  intervals = atoi(argv[1]);

  /* set stack size and create lock... */
  bb_threads_stacksize(65536);
  bb_threads_mutexcreate(0);

  /* make two threads... */
  pids[0] = bb_threads_newthread(do_pi, NULL);
  pids[1] = bb_threads_newthread(do_pi, NULL);

  /* cleanup after two threads (really a barrier sync) */
  bb_threads_cleanup(wait(NULL));
  bb_threads_cleanup(wait(NULL));

  /* print the result */
  printf("Estimation of pi is %14.12lf\n", pi);

  /* check-out */
  exit(0);
}