//---------------------------------------------------------
// 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) : limite(l) {}

    void esperar()
    {
        std::unique_lock<std::mutex> lock(mutex);
        size_t local = uso;
        if (++en_espera[local] < limite)
        {
            // bloqueadas.wait(lock, [&]{ return en_espera[local] == 0; });
            while (en_espera[local] != 0) 
                bloqueadas.wait(lock);
        }
        else
        {
            uso ^= 1;
            en_espera[local] = 0;
            lock.unlock();
            bloqueadas.notify_all();
        }
    }

private:
    std::mutex mutex;
    std::condition_variable bloqueadas;
    std::atomic<size_t> en_espera[2] = {0, 0};
    size_t uso = 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);
}

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