#ifndef semaphore_h
#define semaphore_h

#include <chrono>
#include <mutex>
#include <optional>
#include <semaphore>
#include <stack>
#include <thread>

using namespace std::chrono_literals;

class semaphore
{
public:
    void lock()
    {
        auto backoff = 1us;
        while (!sem.try_acquire()) std::this_thread::sleep_for(backoff *= 2);
    }

    void unlock() { sem.release(); }

private:
    std::binary_semaphore sem{1};
};

template<typename T> class stack
{
public:
    void push(T t)
    {
        std::lock_guard l(s);
        container.push(t);
    }

    std::optional<T> pop()
    {
        std::lock_guard l(s);
        if (!container.empty())
        {
            T data = container.top();
            container.pop();
            return std::optional<T>(data);
        }
        else
        {
            return std::nullopt;
        }
    }

private:
    semaphore s;
    std::stack<T> container;
};

#endif // semaphore_h