C ++ 11 std :: thread以单独的方法连接到主线程

Question

I have the following code:

void do_join(std::thread& t)
{
    t.join();
}

void join_all(std::vector<std::thread>& v)
{
    std::for_each(v.begin(),v.end(),do_join);
}

int main()
{         
    std::vector<std::thread> myThreads;

    for(int i = 1; i <= 3; i++)
    {

        myThreads.push_back(std::thread(threadMethod));

    }


    join_all(myThreads);
}

The goal is to create multiple threads in a loop, add them to a thread vector and then iterating through the vector join them to the main thread.

The problem here is that when my do_join method executes for the first time it joins the thread and waits, not joining any other threads from a vector . That is because my threads are using some conditional variables and waiting for some other tasks to complete. Seems like that do_join method is waiting for just joined thread to complete.

The same thing happens if I try to do for_each directly in the main function.

The idea is to be able to join all these threads to the main thread, not to that let's say do_join 's method thread which I suppose happened here. I could of course join and create them separately, because actually I don't need them to be in a vector (the number of threads is known from the beginning), but I need a vector because each thread in my application is actually created using different method's parameters which I did not included in that sample code. I just do not want a new line for every single thread being created and joined.

Thank you for any help!

Edit: Maybe worth mentioning is that I'm using Ubuntu.

Answer 1

The join method by definition blocks current thread until the one you are trying to join is done:

Blocks the current thread until the thread identified by *this finishes its execution.

( From here. )

That is, it's the purpose of join to block its thread until the other one finishes. If you don't want the thread to be blocked, then don't use join .

You should ask yourself the question: what are you trying to achieve? If you want your main program to proceed only when all the other threads are done, then what you are doing now is right, you'll have to wait for all the threads anyway. Otherwise you might need some way for other threads to signal the main one that they are done.