Asymmetry creates contention between philosophers and this contention is not fair, because one philosopher can eat more often then necessary and other can starve. How to make dinner more fair: add thinking time so after philosopher ate, it should think a bit, so the one who was waiting for fork could eat.
Deadlock prevention using direct prevention method, also knows as asymmetry. It breaks circular wait condition. I make even philosophers take right fork and odd philosophers to take left fork.
| Problem | Basic Dining Philosophers | My Implementation |
|---|---|---|
| Starvation | Some philosophers can eat repeatedly while others starve. | Thinking time adapts based on starvation risk, preventing starvation. |
| Fork Hogging | Philosophers who eat fast can quickly try again. | Philosophers who just ate are forced to wait longer. |
| Race Conditions | All philosophers attempt to grab forks at the same time. | Thinking time staggers philosophers, reducing contention. |
| Fairness | No built-in priority for starving philosophers. | Philosophers with less survival time get priority. |
The code that I used to make system less random and more fair. int silent is used as 1 only when system starts and odd numbered philosophers has imitation of think time, so even philosophers would be always first and system would be more fair.
static int think(t_philo *philo, int silent)
{
long time_to_think;
if (pthread_mutex_lock(&philo->philo_mutex) != 0)
return (MUTEX_LOCK_ERROR);
time_to_think = (philo->sim->time_to_die
- (gettime(MILISECOND) - philo->last_meal_time)
- philo->sim->time_to_eat) / 2;
if (pthread_mutex_unlock(&philo->philo_mutex) != 0)
return (MUTEX_UNLOCK_ERROR);
if (time_to_think < 0)
time_to_think = 0;
if (time_to_think == 0 && silent > 0)
time_to_think = 1;
if (time_to_think > 600)
time_to_think = 200;
if (silent == 0)
write_status(THINKING, philo, DEBUG_MODE);
precise_usleep(time_to_think);
return (SUCCESS);
}