#include <iostream>

#include <thread>

#include <atomic>

#include <random>

#include <array>

using namespace std;

void update_cur_best(atomic<int>& best, int a, int b)

{

if (a < b)

a = b;

auto cur_best = best.load(memory_order_relaxed);

while (cur_best < a && !best.compare_exchange_weak(cur_best, a))

;

}

void run(int max, std::atomic<int>& best)

{

mt19937 generator{random_device{}()};

uniform_int_distribution<int> distribution{0, max};

for (int i = 0; i < 15; ++i)

update_cur_best(best, distribution(generator), distribution(generator));

}

// g++-9 -std=c++2a ./find.best.cpp

int main()

{

atomic<int> best{0};

const int max = 100;

array<thread, 3> threads;

for (auto& t : threads)

t = thread(run, max, sref(best));

for (auto& t : threads)

t.join();

cout << "best = " << best << endl;

return 0;

}