1226_DiningPhilosophers.cpp

#include <condition_variable>
#include <functional>
#include <iostream>
#include <thread>
#include <vector>

class DiningPhilosophers {

private:
    struct ForkWithID {
        int id;
        int ateCount;
        bool leftFork;
    };
    std::vector<ForkWithID> mPhilosophers;

private:
    std::mutex mMutex;
    std::condition_variable mConditionVariable;

public:
    DiningPhilosophers() {
        for (size_t i = 0; i < 5; ++i) {
            mPhilosophers.push_back(ForkWithID{0, 0, false});
        }
    }

    void wantsToEat(int philosopher, std::function<void()> pickLeftFork,
                    std::function<void()> pickRightFork,
                    std::function<void()> eat, std::function<void()> putLeftFork,
                    std::function<void()> putRightFork) {

        std::unique_lock<std::mutex> lock(mMutex);
        mConditionVariable.wait(lock, [=]() {
            int pos = (philosopher == 0 ? 4 : philosopher - 1);
            return (mPhilosophers[philosopher].leftFork == false) &&
                   (mPhilosophers[pos].leftFork == false);
        });

        pickLeftFork();
        mPhilosophers[philosopher].leftFork = true;
        pickRightFork();
        int pos = (philosopher == 0 ? 4 : philosopher - 1);
        mPhilosophers[pos].leftFork = true;
        eat();
        mPhilosophers[philosopher].ateCount += 1;
        putLeftFork();
        mPhilosophers[philosopher].leftFork = false;
        putRightFork();
        mPhilosophers[pos].leftFork = false;
        lock.unlock();
        mConditionVariable.notify_all();
    }
};

int main(int argc, char *argv[]) {
    std::function<void()> pickLeftFork = []() { std::cout << "pickLeftFork\t"; };
    std::function<void()> pickRightFork = []() {
        std::cout << "pickRightFork\t";
    };
    std::function<void()> eat = []() { std::cout << "eat\t"; };
    std::function<void()> putLeftFork = []() { std::cout << "putLeftFork\t"; };
    std::function<void()> putRightFork = []() { std::cout << "putRightFork\t"; };

    DiningPhilosophers diningPhilosophers;

    std::vector<std::thread> threads;
    for (size_t i = 0; i < 5; ++i) {
        threads.push_back(std::thread(
                &DiningPhilosophers::wantsToEat, &diningPhilosophers, i, pickLeftFork,
                pickRightFork, eat, putLeftFork, putRightFork));
    }

    for (auto iter = threads.begin(); iter != threads.end(); ++iter) {
        iter->join();
    }

    return 0;
}