0UT1S's

template<ThreadStateDestructor Destructor>
class ThreadStateCreator
{
private:
    // Initialized to 1, and, if still 1, created on access.
    // Set to 0 on destruction.
    ThreadState* _state;
    G_NO_COPIES_OF_CLS(ThreadStateCreator);

inline bool has_initialized_state() const noexcept
    {
        return this->_state != (ThreadState*)1;
    }

inline bool has_state() const noexcept
    {
        return this->has_initialized_state() && this->_state != nullptr;
    }

public:

// Only one of these, auto created per thread.
    // Constructing the state constructs the MainGreenlet.
    ThreadStateCreator() :
        _state((ThreadState*)1)
    {
    }

~ThreadStateCreator()
    {
        if (this->has_state()) {
            Destructor(this->_state);
        }

this->_state = nullptr;
    }

inline ThreadState& state()
    {
        // The main greenlet will own this pointer when it is created,
        // which will be right after this. The plan is to give every
        // greenlet a pointer to the main greenlet for the thread it
        // runs in; if we are doing something cross-thread, we need to
        // access the pointer from the main greenlet. Deleting the
        // thread, and hence the thread-local storage, will delete the
        // state pointer in the main greenlet.
        if (!this->has_initialized_state()) {
            // XXX: Assuming allocation never fails
            this->_state = new ThreadState;
            // For non-standard threading, we need to store an object
            // in the Python thread state dictionary so that it can be
            // DECREF'd when the thread ends (ideally; the dict could
            // last longer) and clean this object up.
        }
        if (!this->_state) {
            throw std::runtime_error("Accessing state after destruction.");
        }
        return *this->_state;
    }

operator ThreadState&()
    {
        return this->state();
    }

operator ThreadState*()
    {
        return &this->state();
    }

inline int tp_traverse(visitproc visit, void* arg)
    {
        if (this->has_state()) {
            return this->_state->tp_traverse(visit, arg);
        }
        return 0;
    }

};

}; // namespace greenlet

#endif