Question

I intend to fire 2 threads in the main thread, and the main thread should wait till all the 2 child threads finish, this is how I do it.

void *routine(void *arg)
{
    sleep(3);
}

int main()
{
    for (int i = 0; i < 2; i++) {
        pthread_t tid;
        pthread_create(&tid, NULL, routine, NULL);
        pthread_join(&tid, NULL);  //This function will block main thread, right?
    }
}

In the above code, pthread_join indeed makes main thread wait for the child threads, but the problem is, the second thread won’t be created untill the first one finishes. This is not what I want.

What I want is, the 2 threads get created immediatly in the main thread, and then main thread waits for them to finish. Seems like pthread_join cannot do the trick, can it?

I thought, maybe via a semaphore I can do the job, but any other way?

Answer 1

int main()
{
    pthread_t tid[2];
    for (int i = 0; i < 2; i++) {
        pthread_create(&tid[i], NULL, routine, NULL);
    }
    for (int i = 0; i < 2; i++)
       pthread_join(tid[i], NULL);
    return 0;
}