//---------------------------------------------------------
// boost.cc
//---------------------------------------------------------

#include <boost/thread/barrier.hpp>
#include <iostream>
#include <string>
#include <syncstream>
#include <thread>

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

using namespace std::literals;

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

const size_t N = std::thread::hardware_concurrency();

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

boost::barrier 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::osyncstream(std::cout) << antes;
        barrera.wait();
        std::osyncstream(std::cout) << despues;
    }
}

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

int main()
{
    for (size_t i = 0; i < N; ++i)
        std::thread(hebra, i).detach();
    std::this_thread::sleep_for(25ms);
    std::osyncstream(std::cout) << std::flush;
}

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