#include <iostream>
#include <thread>
#include <chrono>
 
void foo()
{
    // simulate expensive operation
    std::this_thread::sleep_for(std::chrono::seconds(1));
}
 
void bar()
{
    // simulate expensive operation
    std::this_thread::sleep_for(std::chrono::seconds(1));
}
 
int main()
{
    std::cout << "starting first helper...\n";
    std::thread helper1(foo);
 
    std::cout << "starting second helper...\n";
    std::thread helper2(bar);
 
    std::cout << "wait main thread a 1 second\n";
    std::this_thread::sleep_for(std::chrono::seconds(1));
 
    std::cout << "waiting for first to finish...\n";
    helper1.join();
 
    std::cout << "wait main thread a 1 second\n";
    std::this_thread::sleep_for(std::chrono::seconds(1));
 
    std::cout << "waiting for second to finish...\n";
    helper2.join();
 
    std::cout << "done!\n";
}

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