/* Portions copyright (c) 2009 Nokia Corporation.  All rights reserved.*/

#undef G_DISABLE_ASSERT

#undef G_LOG_DOMAIN

#include <errno.h>

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#include <unistd.h>

#include <sys/resource.h>

#include <sys/time.h>

#include <sys/poll.h>

#define TRUE 1

#define FALSE 0

static int n_children = 3;

static int n_active_children;

static int n_iters = 10000;

static int write_fds[1024];

static struct pollfd poll_fds[1024];

void

my_pipe (int *fds)

{

  if (pipe(fds) < 0)

    {

      fprintf (stderr, "Cannot create pipe %s\n", strerror (errno));

      exit (1);

    }

}

int

read_all (int fd, char *buf, int len)

{

  size_t bytes_read = 0;

  ssize_t count;

  while (bytes_read < len)

    {

      count = read (fd, buf + bytes_read, len - bytes_read);

      if (count < 0)

	{

	  if (errno != EAGAIN)

	    return FALSE;

	}

      else if (count == 0)

	return FALSE;

      bytes_read += count;

    }

  return TRUE;

}

int

write_all (int fd, char *buf, int len)

{

  size_t bytes_written = 0;

  ssize_t count;

  while (bytes_written < len)

    {

      count = write (fd, buf + bytes_written, len - bytes_written);

      if (count < 0)

	{

	  if (errno != EAGAIN)

	    return FALSE;

	}

      bytes_written += count;

    }

  return TRUE;

}

void

run_child (int in_fd, int out_fd)

{

  int i;

  int val = 1;

  for (i = 0; i < n_iters; i++)

    {

      write_all (out_fd, (char *)&val, sizeof (val));

      read_all (in_fd, (char *)&val, sizeof (val));

    }

  val = 0;

  write_all (out_fd, (char *)&val, sizeof (val));

  exit (0);

}

int

input_callback (int source, int dest)

{

  int val;

  if (!read_all (source, (char *)&val, sizeof(val)))

    {

      fprintf (stderr,"Unexpected EOF\n");

      exit (1);

    }

  if (val)

    {

      write_all (dest, (char *)&val, sizeof(val));

      return TRUE;

    }

  else

    {

      close (source);

      close (dest);

      n_active_children--;

      return FALSE;

    }

}

void

create_child (int pos)

{

  int pid;

  int in_fds[2];

  int out_fds[2];

  my_pipe (in_fds);

  my_pipe (out_fds);

  pid = fork ();

  if (pid > 0)			/* Parent */

    {

      close (in_fds[0]);

      close (out_fds[1]);

      write_fds[pos] = in_fds[1];

      poll_fds[pos].fd = out_fds[0];

      poll_fds[pos].events = POLLIN;

    }

  else if (pid == 0)		/* Child */

    {

      close (in_fds[1]);

      close (out_fds[0]);

      setsid ();

      run_child (in_fds[0], out_fds[1]);

    }

  else				/* Error */

    {

      fprintf (stderr,"Cannot fork: %s\n", strerror (errno));

      exit (1);

    }

}

static double 

difftimeval (struct timeval *old, struct timeval *new)

{

  return

    (new->tv_sec - old->tv_sec) * 1000. + (new->tv_usec - old->tv_usec) / 1000;

}

int 

main (int argc, char **argv)

{

  int i, j;

  struct rusage old_usage;

  struct rusage new_usage;

  if (argc > 1)

    n_children = atoi(argv[1]);

  if (argc > 2)

    n_iters = atoi(argv[2]);

  printf ("Children: %d     Iters: %d\n", n_children, n_iters);

  n_active_children = n_children;

  for (i = 0; i < n_children; i++)

    create_child (i);

  getrusage (RUSAGE_SELF, &old_usage);

  while (n_active_children > 0)

    {

      int old_n_active_children = n_active_children;

      poll (poll_fds, n_active_children, -1);

      for (i=0; i<n_active_children; i++)

	{

	  if (poll_fds[i].events & (POLLIN | POLLHUP))

	    {

	      if (!input_callback (poll_fds[i].fd, write_fds[i]))

		write_fds[i] = -1;

	    }

	}

      if (old_n_active_children > n_active_children)

	{

	  j = 0;

	  for (i=0; i<old_n_active_children; i++)

	    {

	      if (write_fds[i] != -1)

		{

		  if (j < i)

		    {

		      poll_fds[j] = poll_fds[i];

		      write_fds[j] = write_fds[i];

		    }

		  j++;

		}

	    }

	}

    }

  getrusage (RUSAGE_SELF, &new_usage);

  printf ("Elapsed user: %g\n",

	   difftimeval (&old_usage.ru_utime, &new_usage.ru_utime));

  printf ("Elapsed system: %g\n",

	   difftimeval (&old_usage.ru_stime, &new_usage.ru_stime));

  printf ("Elapsed total: %g\n",

	  difftimeval (&old_usage.ru_utime, &new_usage.ru_utime) +	   

	   difftimeval (&old_usage.ru_stime, &new_usage.ru_stime));

  printf ("total / iteration: %g\n",

	   (difftimeval (&old_usage.ru_utime, &new_usage.ru_utime) +	   

	    difftimeval (&old_usage.ru_stime, &new_usage.ru_stime)) /

	   (n_iters * n_children));

  return 0;

}