Philosophers

Project in Ecole42. The purpose of this project is to learn how to work with threads, mutex, semaphores.

Discription

It is classic task about dining philosophers problem. For do this task, you need know some rules:

• One or more philosophers sit at a round table
• The philosophers alternatively eat, think, or sleep. While they are eating, they are not thinking nor sleeping; while thinking, they are not eating nor sleeping; and, of course, while sleeping, they are not eating nor thinking.
• There are also forks on the table. There are as many forks as philosophers.
• Because eating with only one fork is very inconvenient, a philosopher takes two forks to eat, one in each hand.
• When a philosopher has finished eating, they put their forks back on the table and start sleeping. Once awake, they start thinking again. The simulation stops when a philosopher dies of starvation.
• Every philosopher needs to eat and should never starve.
• Philosophers don’t speak with each other.
• Philosophers don’t know if another philosopher is about to die.
• No need to say that philosophers should avoid dying.

Programm take 4 or 5 arguments and looks like:

./philo number_of_philosophers time_to_die time_to_eat time_to_sleep number_of_times_each_philosopher_must_eat

• number_of_philosophers: The number of philosophers and also the number of forks.
• time_to_die (in milliseconds): If a philosopher didn’t start eating time_to_die milliseconds since the beginning of their last meal or the beginning of the simulation, they die.
• time_to_eat (in milliseconds): The time it takes for a philosopher to eat. During that time, they will need to hold two forks.
• time_to_sleep (in milliseconds): The time a philosopher will spend sleeping.
• number_of_times_each_philosopher_must_eat (optional argument): If all philosophers have eaten at least number_of_times_each_philosopher_must_eat times, the simulation stops. If not specified, the simulation stops when a philosopher dies.

In program runtime any state change of a philosopher must be formatted as follows:

timestamp_in_ms X has taken a fork
timestamp_in_ms X is eating
timestamp_in_ms X is sleeping
timestamp_in_ms X is thinking
timestamp_in_ms X died

timestamp_in_ms and X replace by:

• timestamp_in_ms - the current timestamp in milliseconds
• X - philosopher number (from 1 to number_of_philosopher)

Specific rules

Mandatory path:

• Each philosopher should be a thread.
• There is one fork between each pair of philosophers. Therefore, if there are several philosophers, each philosopher has a fork on their left side and a fork on their right side. If there is only one philosopher, there should be only one fork on the table.
• To prevent philosophers from duplicating forks, you should protect the forks state with a mutex for each of them.

Bonus part:

• All the forks are put in the middle of the table.
• They have no states in memory but the number of available forks is represented by a semaphore.
• Each philosopher should be a process. But the main process should not be a philosopher.

Evaluated by moulinette