gistfile1.cpp

boost::optional<GCPtr<>> object;
std::mutex mutex;
std::vector<std::function<void(GCPtr<>)>> receiveCallbacks;
std::vector<std::function<GCPtr<>()>> sendCallbacks;

template<typename F>
void receive(F receiveCallback) {
    boost::optional<GCPtr<>> value;
    {
        std::lock_guard<decltype(mutex)> lock(mutex);
        if (!object.empty()) {
            value = std::move(object);
            if (!sendCallbacks.empty()) {
                auto sendCallback = detail::takeRandomElement(sendCallbacks);
                object = sendCallback();
            }
        } else {
            receiveCallbacks.push_back(std::move(receiveCallback));
        }
    }
    if (value) {
        receiveCallback(*value);
    }
}