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https://github.com/hyxogen/philosophers

A 42 common core project about philosophy and threads
https://github.com/hyxogen/philosophers

42projects c dining-philosophers-problem mutexes pthreads semaphores

Last synced: about 1 year ago
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A 42 common core project about philosophy and threads

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README 

          
philosophers

============

Philosophers is a 42 core curriculum project for learning about

threads, mutexes and semaphores by solving a slightly modified version

of the dining philosophers problem

(https://en.wikipedia.org/wiki/Dining_philosophers_problem).



Overview

============

x One or more philosophers sit at a round table.

  There is a large bowl of spaghetti in the middle of the table.

x 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.

x There are also forks on the table. There are as many forks as

  philosophers

x Because serving and eating spaghetti with only one fork is very

  inconvenient, a philosopher takes their right and their left forks to

  eat, one in each hand.

x 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.

x Every philosopher needs to eat and should never starve.

x Philosophers don’t speak with each other.

x Philosophers don’t know if another philosopher is about to die.

x No need to say that philosophers should avoid dying!



Global rules

============

x Global variables are forbidden

x The program must take the following arguments:

  number_of_philosophers time_to_die time_to_eat time_to_sleep

  [number_of_times_each_philosopher_must_eat]

  x number_of_philosophers: the number of philosophers and also the

    number of forks

  x 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, the philosopher dies

  x time_to_eat (in milliseconds): the time it takes for a philosopher

    to eat. During this time, the philosopher will need to hold two

    forks

  x time_to_sleep (in milliseconds): the time a philosopher will spend

    sleeping

  x number_of_times_each_philosopher_must_eat (optional): if all

    philosophers have eaten at least

    number_of_times_each_philosopher_must_eat times, then the

    simulation stops. If not specified, the simulation stops when a

    philosopher dies

x Each philosopher has a number ranged from 1 to

  number_of_philosophers

x Philosopher number 1 sits next to philosopher

  number_of_philosophers. Any other philosopher number N sits between

  philosopher number N - 1 and philosopher number N + 1

x Any state change of a philosopher must be formatted as follows:

  x timestamp_in_ms X has taken a fork

  x timestamp_in_ms X is eating

  x timestamp_in_ms X is sleeping

  x timestamp_in_ms X is thinking

  x timestamp_in_ms X died

  (with timestamp_in_ms replaced by the current timestamp in

  milliseconds and X with the philosopher number)

x A displayed state message should not be mixed up with another

  message.

x A message announcing a philosopher died should be displayed within

  10 ms after the actual death of the philosopher

x Philosophers should avoid dying



Mandatory part rules

============

x Each philosophers should be a thread

x 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 fore on their right side. If there is only one

  philosopher, there should be only one fork on the table

x To prevent philosophers from duplicating forks, you should protect

  the forks state with a mutex for each of them



Allowed external functions:

memset, printf, malloc, free, write, usleep, gettimeofday,

pthread_create, pthread_detach, pthread_join, pthread_mutex_init,

pthread_mutex_destroy, pthread_mutex_lock, pthread_mutex_unlock



My mandatory solution

============

x All philosophers always try to take both forks, and hold them for as

  long as is needed (this means that they won't drop a fork if the

  other side isn't available)

x All uneven philosophers will sleep `eat_time` at the beginning of

  the project



Bonus part rules

============

x All forks are put in the middle of the table

x They have no states in memory but the number of available forks is

  represented by a semaphore

x Each philosopher should be a process, but the main process should

  not be a philosopher



Allowed external functions:

memset, printf, malloc, free, write, fork, kill, exit, pthread_create,

pthread_detach, pthread_join, usleep, gettimeofday, waitpid, sem_open,

sem_close, sem_post, sem_wait, sem_unlink



My bonus solution

============

For the bonus I just let all the philosophers loose and try to take

forks as they see fit as that seems to be the best solution when the

pile of forks is in the middle.



Special Thanks

============

Special Thanks to dnoom and mjoosten for pointing out that philosopher

ids should start at 1 and not at 0