Test 2: Dining Philosophers

In the second test we will search for a solution of a typical computer science problem. Five philosophers sit at a round table with bowls of rice. Chopsticks are placed between each pair of adjacent philosophers.

Each philosopher must alternately think and eat. However, a philosopher can only eat rice when he has both left and right chopstick. Each chopstick can be held by only one philosopher and so a philosopher can use the chopstick only if it is not being used by another philosopher. After he finishes eating, he needs to put down both chopsticks so they become available to others. A philosopher can take the chopstick on his right or the one on his left as they become available, but cannot start eating before getting both of them.

There is an infinite amount of rice in the bowls.

You need to design a program which makes sure all philosophers can think and eat. There are many solutions to this problem but you are adviced to use a waiter which serves the table.

In the framework a PhilosopherActor class is provided. This actor has the methods think and eat. If a philosopher is in the thinking state the think method needs to be called. If the philosopher is in the eating state the eat method needs to be called. A single philosopher implementation is given below:

import time
from sphof import LonePhilosopherActor

class SinglePhilosopher(LonePhilosopherActor):

    def setup(self):
        self.state_hungry = True
        self.switch_at = time.time() + 5      # switch state every 5s
        self.enlightenment = None
        self.topics = []                      # food for thought

    def update(self):
        if time.time() > self.switch_at or not(len(self.topics)):
            # it's time to switch state
            self.switch_at = time.time() + 5    # set next state switch timestamp
            self.state_hungry = not(self.state_hungry)
            if self.state_hungry:
                print("Jay food! Eating....", len(self.topics))
            else:
                print("Hmmmmm... let me think...", len(self.topics))

        if not self.state_hungry:
            enlightenment = self.think()
            if enlightenment:
                print("Eureka:", enlightenment, len(self.topics))
        else:
            self.eat()


if __name__ == '__main__':
    test = SinglePhilosopher("Descartes")
    test.run()

You can use this implementation for your multiple philosophers implementation.