CODEWITHSUNDEEP
c++multithreadingqueue
peterjtk
peterjtk

Reputation: 41

Pass a queue between threads in c++

I'm looking for a way to pass a queue between threads in c++, below is a very basic outline what I want to do. It works as a function but I need to use a separate thread as both the task and main will have separate loops to perform.

here is the function:

void task1(queue <bool> &qPass)
{
    bool bits[5] = { 1, 0, 0, 1, 1 };

    for (int i = 0; i < 5; i++)
    {
        qPass.push(bits[i]);
    }

    cout << "Task:\tpush complete\t(" << qPass.size() << ")" << endl;
}

the main

int main()
{
    queue <bool> qPass;
    int n;

    //thread task(task1, qPass);//thread call doesnt work
    //task.join();

    task1(qPass);//function call works

    n = qPass.size();
    cout << "Main:\t";
    for (int i = 0; i < n; i++)
    {
        cout << qPass.front();
        qPass.pop();
    }
    cout << "\t(" << n << ")" << endl;

    cin.get();
    return 0;
}

If I comment the function call and uncomment the thread calls it will run but the queue in main isn't filled. Thanks in advance.

Upvotes: 1

Views: 3256

Answers (1)

Kerrek SB
Kerrek SB

Reputation: 476950

You need to wrap the argument in a reference wrapper:

std::thread task(task1, std::ref(qPass));
//                      ^^^^^^^^

(Otherwise, the thread objects binds a local, private copy of the queue, and your main queue is never touched.)

Upvotes: 3

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