atomic and thread example

// example of thread and atomic
// g++ prog.cc -Wall -Wextra -I/opt/wandbox/boost-1.73.0/gcc-head/include -std=gnu++2b
//
#include <iostream>
#include <cstdlib>
#include <string>
#include <thread>
#include <atomic>

std::atomic_int integer{0};
std::atomic_bool flagA{false};
std::atomic_bool flagB{false};

void thread1()
{
    flagB.store(true, std::memory_order_release);                 // set memory
    if(flagA.load(std::memory_order_acquire))                     // check other memory
        ++g_integer;                                                // set global intger
}
void thread2()
{
    flagA.store(true, std::memory_order_release);
    if(flagB.load(std::memory_order_acquire))
        ++g_integer;
}
void thread3()
{
    flagA.store(false, std::memory_order_release);
    if(flagB.load(std::memory_order_acquire))
        --g_integer;
}
int main()
{
    ++integer;
    flagA.store(true, std::memory_order_release);

    std::thread firstThread(&thread1);
    std::thread secondThread(&thread2);
    firstThread.join();
    secondThread.join();
    std::cout << g_integer << " " << flagA.load(std::memory_order_acquire) << " " << flagB.load(std::memory_order_acquire) << std::endl;

    std::thread firstThread1(&thread3);
    std::thread secondThread1(&thread1);
    firstThread1.join();
    secondThread1.join();
    std::cout << g_integer << " " << flagA.load(std::memory_order_acquire) << " " << flagB.load(std::memory_order_acquire) << std::endl;

    std::thread firstThread2(&thread2);
    std::thread secondThread2(&thread1);
    firstThread2.join();
    secondThread2.join();
    std::cout << g_integer << " " << flagA.load(std::memory_order_acquire) << " " << flagB.load(std::memory_order_acquire) << std::endl;

    return 0;
}