#!/usr/bin/python3
# -*- coding: utf-8 -*-

import threading
import random
import time


# Dining philosophers, 5 Phillies with 5 forks. Must have two forks to eat.
#
# Deadlock is avoided by never waiting for a fork while holding a fork (locked)
# Procedure is to do block while waiting to get first fork, and a nonblocking
# acquire of second fork.  If failed to get second fork, release first fork,
# swap which fork is first and which is second and retry until getting both.
#

class Philosopher(threading.Thread):

    running = True

    def __init__(self, xname, forkOnLeft, forkOnRight):
        threading.Thread.__init__(self)
        self.name = xname
        self.forkOnLeft = forkOnLeft
        self.forkOnRight = forkOnRight

    def run(self):
        while(self.running):
            #  Philosopher is thinking (but really is sleeping).
            time.sleep( random.uniform(3,13))
            print ('%s is hungry.' % self.name)
            self.dine()

    def dine(self):
        fork1, fork2 = self.forkOnLeft, self.forkOnRight

        while self.running:
            pass
            fork1.acquire(True)
            locked = fork2.acquire(False)
            if locked: break
            fork1.release()
            print ('%s swaps forks' % self.name)
            fork1, fork2 = fork2, fork1
        else:
            return

        self.dining()
        fork2.release()
        fork1.release()

    def dining(self):
        print ('%s starts eating '% self.name)
        time.sleep(random.uniform(1,10))
        print ('%s finishes eating and leaves to think.' % self.name)

def DiningPhilosophers():
    forks = [threading.Lock() for n in range(5)]
    philosopherNames = ('Aristotle','Kant','Buddha','Marx', 'Russel')

    philosophers= [Philosopher(philosopherNames[i], forks[i%5], forks[(i+1)%5]) \
            for i in range(5)]

    random.seed(507129)
    Philosopher.running = True
    for p in philosophers: p.start()
    time.sleep(100)
    Philosopher.running = False
    print ("Now we're finishing.")

DiningPhilosophers()