C++ Join multiple threads

Question

I would like to do a for-loop which creates more threads.

I've tried with:

int i;
for (i = 0; i < 10; i++) {
    thread t1(nThre);
    t1.join();
    cout << "Joined thread n'" << i << '\n';
}

But it does not work. nThre is called sequentially (it is a simple void routine).

I'm also asking if I can use a pre-increment as i is just an int , so: ++i insted of i++ , which should be more performant.

Answer 1

Your problem is that you start a thread, and join it before starting the next one. You should do like this :

int i;
vector<thread> threads;

for (i = 0; i < 10; i++) {
    threads.push_back(thread(nThre));
    cout << "Started thread n'" << i << "\n";
}

for (i = 0; i < 10; i++) {
    threads[i].join();
    cout << "Joined thread n'" << i << "\n";
}

First, you start all your threads, then you wait until they are finished.

For the difference between i++ and ++i , since i is a integer, it makes no difference here. See this answer for more details.