/* yield_count.c */


#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <sched.h>

typedef void *(*create_func)(void *);

static int child_ran = 0;
static int parent_ran = 0;
static int *child_run, *parent_run;

static void *child_function(int *runs)
{
    register int i, run = *runs;

    child_ran = 1;
    for (i = 0; i < run; i++)
    {
        for (child_run[i] = 0; !parent_ran; child_run[i]++)
        {
            sched_yield ();
        }
        parent_ran = 0;
        child_ran = 1;
    }

    return NULL;
}

int main(int argc, char *argv[])
{
    int i, runs;
    pthread_t child_thread;


    if (argc != 2)
    {
        fputs("Usage: yield runs, where runs is the number of times to try yielding\n", stderr);
        return EXIT_FAILURE;
    }

	i = 1;

    runs = atoi (argv[i]);
    child_run = (int *) malloc (runs * sizeof (int));
    parent_run = (int *) malloc (runs * sizeof (int));

    pthread_create(&child_thread, NULL, (create_func) child_function, &runs);

    parent_ran = i;
    for (i = 0; i < runs; i++)
    {
        for (parent_run[i] = 0; !child_ran; parent_run[i])
        {
            sched_yield ();
        }
        child_ran = 0;
        parent_ran = 1;
    }

    pthread_join(child_thread, NULL);

    puts("Parent statistics:");
    for (i = 0; i < runs; i++)
    {
        printf ("  Run %d: %d yields before the child ran\n", i, parent_run[i]);
    }

    puts("Child statistics:");
    for (i = 0; i < runs; i++)
    {
        printf ("  Run %d: %d yields before the parent ran\n", i, child_run[i]);
    }

    free (child_run);
    free (parent_run);
    return EXIT_SUCCESS;
}