concurrent_fizzbuzz.cpp

class FizzBuzz {
private:
    int n;
    int next;
    
    mutex m;
    map<int, condition_variable*> waiters;

public:
    FizzBuzz(int n) {
        this->n = n;
        this->next = 1;
    }

    // printFizz() outputs "fizz".
    void fizz(function<void()> printFizz) {
        run(3, [](int val) { return val % 5 != 0; }, [&](int) { printFizz(); });
    }

    // printBuzz() outputs "buzz".
    void buzz(function<void()> printBuzz) {
        run(5, [](int val) { return val % 3 != 0; }, [&](int) { printBuzz(); });
    }

    // printFizzBuzz() outputs "fizzbuzz".
	  void fizzbuzz(function<void()> printFizzBuzz) {
        run(15, [](int val) { return true; }, [&](int) { printFizzBuzz(); });
    }

    // printNumber(x) outputs "x", where x is an integer.
    void number(function<void(int)> printNumber) {
        run(1, [](int val) { return val % 3 != 0 && val % 5 != 0; }, printNumber);
    }
    
private:
    void run(int step, function<bool(int)> cond, function<void(int)> print)
    {
        condition_variable cv;
        for (auto i = step; i <= n; i += step)
        {
            if (cond(i))
            {
                unique_lock lk(m);
                if (this->next != i)
                {
                    this->waiters[i] = &cv;
                    cv.wait(lk, [&]() { return this->next == i; });
                }
                print(i);
                ++this->next;
                auto it = this->waiters.find(this->next);
                if (it != this->waiters.end())
                {
                    auto waiter_cv = it->second;
                    this->waiters.erase(it);
                    waiter_cv->notify_one();
                }
            }
        }
    }
};