// C++11 does not support std::shared_mutex and std::shared_lock yet.
// This piece of Code is based on the proposal for C++14
#include <mutex>
#include <condition_variable>
#include <climits>

namespace lean {
class shared_mutex {
    std::mutex              m_mutex;
    std::condition_variable m_gate1;
    std::condition_variable m_gate2;
    unsigned                m_state;

    static constexpr unsigned write_entered = 1u << (sizeof(unsigned)*8 - 1);
    static constexpr unsigned readers       = ~write_entered;

public:
    shared_mutex();
    ~shared_mutex();

    shared_mutex(shared_mutex const &) = delete;
    shared_mutex(shared_mutex &&) = delete;
    shared_mutex& operator=(shared_mutex const &) = delete;
    shared_mutex&& operator=(shared_mutex &&) = delete;

    void lock();
    bool try_lock();
    void unlock();

    void lock_shared();
    bool try_lock_shared();
    void unlock_shared();
};

class shared_lock {
    shared_mutex & m_mutex;
public:
    shared_lock(shared_mutex & m):m_mutex(m) { m_mutex.lock_shared(); }
    ~shared_lock() { m_mutex.unlock_shared(); }
};

class unique_lock {
    shared_mutex & m_mutex;
public:
    unique_lock(shared_mutex & m):m_mutex(m) { m_mutex.lock(); }
    ~unique_lock() { m_mutex.unlock(); }
};
}