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/* linux-dp.c --- dining philosophers, on LinuxThreads

   Jim Blandy <jimb@cygnus.com> --- March 1999  */

/* It's okay to edit this file and shift line numbers around.  The

   tests use gdb_get_line_number to find source locations, so they

   don't depend on having certain line numbers in certain places.  */

#include <stdarg.h>

#include <stdlib.h>

#include <stdio.h>

#include <pthread.h>

#include <sys/time.h>

#include <sys/types.h>

/* The number of philosophers at the table.  */

int num_philosophers;

/* Mutex ordering -

   If you want to lock a mutex M, all the mutexes you have locked

   already must appear before M on this list.

   fork_mutex[0]

   fork_mutex[1]

   ...

   fork_mutex[num_philosophers - 1]

   stdout_mutex

   random_mutex

*/

/* You must hold this mutex while writing to stdout.  */

pthread_mutex_t stdout_mutex;

/* You must hold this mutex while calling any of the random number

   generation routines.  */

pthread_mutex_t random_mutex;

/* array of mutexes, one for each fork; fork_mutex[i] is to the left

   of philosopher i.  A philosopher is holding fork i iff his/her

   thread has locked fork_mutex[i].  */

pthread_mutex_t *fork_mutex;

/* array of threads, one representing each philosopher.  */

pthread_t *philosophers;

void *

xmalloc (size_t n)

{

  void *p = malloc (n);

  if (! p)

    {

      fprintf (stderr, "out of memory\n");

      exit (2);

    }

  return p;

}

void

shared_printf (char *format, ...)

{

  va_list ap;

  va_start (ap, format);

  pthread_mutex_lock (&stdout_mutex);

  vprintf (format, ap);

  pthread_mutex_unlock (&stdout_mutex);

  va_end (ap);

}

int

shared_random ()

{

  static unsigned int seed;

  int result;

  pthread_mutex_lock (&random_mutex);

  result = rand_r (&seed);

  pthread_mutex_unlock (&random_mutex);

  return result;

}

void

my_usleep (long usecs)

{

  struct timeval timeout;

  timeout.tv_sec = usecs / 1000000;

  timeout.tv_usec = usecs % 1000000;

  select (0, 0, 0, 0, &timeout);

}

void

random_delay ()

{

  my_usleep ((shared_random () % 2000) * 100);

}

void

print_philosopher (int n, char left, char right)

{

  int i;

  shared_printf ("%*s%c %d %c\n", (n * 4) + 2, "", left, n, right);

}

void *

philosopher (void *data)

{

  int n = * (int *) data;

  print_philosopher (n, '_', '_');

#if 1

  if (n == num_philosophers - 1)

    for (;;)

      {

        /* The last philosopher is different.  He goes for his right

           fork first, so there is no cycle in the mutex graph.  */

        /* Grab the right fork.  */

        pthread_mutex_lock (&fork_mutex[(n + 1) % num_philosophers]);

        print_philosopher (n, '_', '!');

        random_delay ();

        /* Then grab the left fork. */

        pthread_mutex_lock (&fork_mutex[n]);

        print_philosopher (n, '!', '!');

        random_delay ();

        print_philosopher (n, '_', '_');

        pthread_mutex_unlock (&fork_mutex[n]);

        pthread_mutex_unlock (&fork_mutex[(n + 1) % num_philosophers]);

        random_delay ();

      }

  else

#endif

    for (;;)

      {

        /* Grab the left fork. */

        pthread_mutex_lock (&fork_mutex[n]);

        print_philosopher (n, '!', '_');

        random_delay ();

        /* Then grab the right fork.  */

        pthread_mutex_lock (&fork_mutex[(n + 1) % num_philosophers]);

        print_philosopher (n, '!', '!');

        random_delay ();

        print_philosopher (n, '_', '_');

        pthread_mutex_unlock (&fork_mutex[n]);

        pthread_mutex_unlock (&fork_mutex[(n + 1) % num_philosophers]);

        random_delay ();

      }

  return (void *) 0;

}

int

main (int argc, char **argv)

{

  num_philosophers = 5;

  /* Set up the mutexes.  */

  {

    pthread_mutexattr_t ma;

    int i;

    pthread_mutexattr_init (&ma);

    pthread_mutex_init (&stdout_mutex, &ma);

    pthread_mutex_init (&random_mutex, &ma);

    fork_mutex = xmalloc (num_philosophers * sizeof (fork_mutex[0]));

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

      pthread_mutex_init (&fork_mutex[i], &ma);

    pthread_mutexattr_destroy (&ma);

  }

  /* Set off the threads.  */

  {

    int i;

    int *numbers = xmalloc (num_philosophers * sizeof (*numbers));

    pthread_attr_t ta;

    philosophers = xmalloc (num_philosophers * sizeof (*philosophers));

    pthread_attr_init (&ta);

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

      {

        numbers[i] = i;

        /* linuxthreads.exp: create philosopher */

        pthread_create (&philosophers[i], &ta, philosopher, &numbers[i]);

      }

    pthread_attr_destroy (&ta);

  }

  /* linuxthreads.exp: info threads 2 */

  sleep (1000000);

  /* Drink yourself into oblivion.  */

  for (;;)

    sleep (1000000);

  return 0;

}