Execution of a C++ code block only one (C++11)

cpponce.cpp

#include <mutex>
#include <condition_variable>
#include <functional>
#include <iostream>
#include <thread>
#include <chrono>

class OnceHard
{
public:
	OnceHard(std::function<void()> x) : action(x) {}

	bool operator()()
	{
		std::unique_lock<std::mutex> lk(mtx);
		if(!done)
		{
			action();
			done = true;
			return true;
		}
		else
			return false;
	}
private:
	bool done = false;
	std::function<void()> action;
	std::mutex mtx;
};


class Once
{
public:
	// inited before threads spawn
	Once(std::function<void()> x) : action(x) {}

	bool operator()()
	{
		std::unique_lock<std::mutex> lk(mtx);
		if(state == State::Not)
		{
			state = State::Doing;
			lk.unlock(); // momentarly release
			action(); // run once
			lk.lock(); // lock again
			state = State::Done;
			cv.notify_all();
			return true;
		}
		else 
		{
			std::cerr << "waitcomplete\n";
			cv.wait(lk, [this]{return this->state == State::Done;});
			std::cerr << "waitdone\n";
			return false;
		}
	}
private:
	enum class State { Not, Doing, Done};
	State state = State::Not;
	std::function<void()> action;
	std::mutex mtx;
	std::condition_variable cv;
};

int main(int argc, char * argv[])
{
	OnceHard once([] () {
			std::cerr << "oncestart\n";
		 	std::this_thread::sleep_for(std::chrono::seconds(1));
			std::cerr << "onceend\n";
	});
	std::function<void()> waits = [&] ()
	{
		std::cout << "got " << once() << std::endl;
	};

	std::thread t1(waits), t2(waits), t3(waits);
    t1.join(); 
    t2.join(); 
    t3.join();
    return 0;
}