//---------------------------------------------------------
// monitor2.cc
//---------------------------------------------------------

#include <condition_variable>
#include <iostream>
#include <mutex>
#include <string>
#include <thread>

//---------------------------------------------------------

using namespace std::literals;

//---------------------------------------------------------

const size_t N = 8;

//---------------------------------------------------------

class barrera_t
{
public:
    barrera_t(size_t l) : contador(l), limite(l) {}

    void esperar()
    {
        std::unique_lock<std::mutex> lock(mutex);

        size_t gen = generacion;

        if (--contador == 0)
        {
            ++generacion;
            contador = limite;
            lock.unlock();
            bloqueadas.notify_all();
        }
        else
        {
            // bloqueadas.wait(lock, [&]{ return gen != generacion; });
            while (gen == generacion)
                bloqueadas.wait(lock);
        }
    }

private:
    std::mutex mutex;
    std::condition_variable bloqueadas;
    size_t contador = 0, generacion = 0, limite;
} barrera(N);

//---------------------------------------------------------

void hebra(size_t yo)
{
    std::string antes = std::to_string(yo) + ": antes\n",
                despues = std::to_string(yo) + ": después\n";
    while (true)
    {
        std::cout << antes;
        barrera.esperar();
        std::cout << despues;
    }
}

//---------------------------------------------------------

int main()
{
    for (size_t i = 0; i < N; ++i)
        std::thread(hebra, i).detach();
    std::this_thread::sleep_for(1ms);
}

//---------------------------------------------------------