Task: Dining philosophers


C++: #include <algorithm>
#include <array>
#include <chrono>
#include <iostream>
#include <mutex>
#include <random>
#include <string>
#include <string_view>
#include <thread>

const int timeScale = 42;  

void Message(std::string_view message)
{
    
    static std::mutex cout_mutex;
    std::scoped_lock cout_lock(cout_mutex);
    std::cout << message << std::endl;
}

struct Fork {
    std::mutex mutex;
};

struct Dinner {
    std::array<Fork, 5> forks;
    ~Dinner() { Message("Dinner is over"); }
};

class Philosopher
{
    
    
    std::mt19937 rng{std::random_device {}()};

    const std::string name;
    Fork& left;
    Fork& right;
    std::thread worker;

    void live();
    void dine();
    void ponder();
public:
    Philosopher(std::string name_, Fork& l, Fork& r)
    : name(std::move(name_)), left(l), right(r), worker(&Philosopher::live, this)
    {}
    ~Philosopher()
    {
        worker.join();
        Message(name + " went to sleep.");
    }
};

void Philosopher::live()
{
    for(;;) 
    {
        {
            
            
            std::scoped_lock dine_lock(left.mutex, right.mutex);

            dine();

            
        }
        
        ponder();
    }
}

void Philosopher::dine()
{
    Message(name + " started eating.");

    
    thread_local std::array<const char*, 3> foods {"chicken", "rice", "soda"};
    thread_local std::array<const char*, 3> reactions {
        "I like this %s!", "This %s is good.", "Mmm, %s..."
    };
    thread_local std::uniform_int_distribution<> dist(1, 6);
    std::shuffle(    foods.begin(),     foods.end(), rng);
    std::shuffle(reactions.begin(), reactions.end(), rng);
    
    constexpr size_t buf_size = 64;
    char buffer[buf_size];
    for(int i = 0; i < 3; ++i) {
        std::this_thread::sleep_for(std::chrono::milliseconds(dist(rng) * timeScale));
        snprintf(buffer, buf_size, reactions[i], foods[i]);
        Message(name + ": " + buffer);
    }
    std::this_thread::sleep_for(std::chrono::milliseconds(dist(rng)) * timeScale);

    Message(name + " finished and left.");
}

void Philosopher::ponder()
{
    static constexpr std::array<const char*, 5> topics {{
        "politics", "art", "meaning of life", "source of morality", "how many straws makes a bale"
    }};
    thread_local std::uniform_int_distribution<> wait(1, 6);
    thread_local std::uniform_int_distribution<> dist(0, topics.size() - 1);
    while(dist(rng) > 0) {
        std::this_thread::sleep_for(std::chrono::milliseconds(wait(rng) * 3 * timeScale));
        Message(name + " is pondering about " + topics[dist(rng)] + ".");
    }
    std::this_thread::sleep_for(std::chrono::milliseconds(wait(rng) * 3 * timeScale));
    Message(name + " is hungry again!");
}

int main()
{
    Dinner dinner;
    Message("Dinner started!");
    
    std::array<Philosopher, 5> philosophers {{
            {"Aristotle",   dinner.forks[0], dinner.forks[1]},
            {"Democritus",  dinner.forks[1], dinner.forks[2]},
            {"Plato",       dinner.forks[2], dinner.forks[3]},
            {"Pythagoras",  dinner.forks[3], dinner.forks[4]},
            {"Socrates",    dinner.forks[4], dinner.forks[0]},
    }};
    Message("It is dark outside...");
}






Python: import threading
import random
import time










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):
            
            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:
            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','Spinoza','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()