system_init.cpp

#include <iostream>
#include <thread>
#include <mutex>

using namespace std;


void SystemInit(){
    cout << "hello world! "<< endl;
}


void SystemInitOnce(){
    static std::once_flag flag;
    std::call_once(flag, SystemInit);
}


int main(){
    thread th(SystemInitOnce);
    th.join();


    for(int i=0;i<4;i++){
        cout << "try to init once again ? " << endl;
        thread th(SystemInitOnce);
        th.join();
    }
    return 0;
}