error C2248 while using std::atomic<bool>::atomic

Question

Firstly, pardon me for the long post.

I am using boost::lockfree::spsc_queue to run on two separate threads to process FIX messages. I am using quickfix for converting FIX strings from a file to convert to FIX Messages. I want to be able to pass the queue as a pointer to both threads and a boolean value that indicates whether there are still messages to be processes.

I am getting the following error:

Please refer the code below.

It is based of an example in boost documentation. (Waitfree Single-Producer/Single-Consumer Queue)

http://www.boost.org/doc/libs/1_55_0/doc/html/lockfree/examples.html

I have been trying different ways to transfer the value of running and pqFixMessages to the two threads but nothing seams to work as of now. I will appreciate any suggestions.

'std::atomic<bool>::atomic' : cannot access private member declared in class 'std::atomic<bool>

Description:

Producer thread reads a file, creates FIX messages and pushes them in the queue.

Consumer thread reads the queue and processes these messages. As of now, I am just displaying the session id's for debugging.

Main has a pointer to the queue that is passed on to both the threads.

Further Context: After this works, I want producer and consumer to be separate classes.

#include <iostream>
#include <thread>
#include <atomic>
#include <fstream>
#include <quickfix\Message.h>
#include <boost\lockfree\spsc_queue.hpp>


using namespace std;
using namespace boost::lockfree;

void producer(spsc_queue<FIX::Message, capacity<1024>> * pqFixMessages, std::atomic<bool> running) {
    std::string line;
    std::ifstream fixMessageStream(<filename>);
    FIX::Message currentMessage;
    while (fixMessageStream) {
        std::getline(fixMessageStream, line);
        try {
            // Erases the timestamp on messages
            currentMessage = FIX::Message(line.erase(0, 25));
            pqFixMessages->push(currentMessage);
        } catch (std::exception& ex) {
        }
    }
    running = false;
}

std::atomic<bool> done(false); 

void consumer(spsc_queue<FIX::Message, capacity<1024>> * pqFixMessages, std::atomic<bool> running) {
    FIX::Message frontOfTheQueueMessage;
    while(!pqFixMessages->empty() || running) {
        if (!pqFixMessages->empty()) {
            pqFixMessages->pop(frontOfTheQueueMessage);
            cout << frontOfTheQueueMessage.getSessionID() << endl;
        }
    }
}

int main(int argc, char * argv[]) {

    spsc_queue<FIX::Message, capacity<1024>> * pqFixMessages = 
        new spsc_queue<FIX::Message, capacity<1024>>();

    std::atomic<bool> running(true);

    thread producerThread(producer, pqFixMessages, ref(running));
    cout << "Entered Producer Thread" << endl;
    thread consumerThread(consumer, pqFixMessages, ref(running));
    cout << "Entered Consumer Thread" << endl;

    producerThread.join();
    cout << "Joined Producer Thread" << endl;
    done = true;
    consumerThread.join();
    cout << "Joined Consumer Thread" << endl;

    delete pqFixMessages;

    std::cin.get();

    return 0;

}

Answer 1

std::atomics are not copyable.

Hence, passing them by value to a function is not possible.

This is for a reason. Usually, attempting to pass them by value indicates a programming error. They are typically used as synchronization primitives and you cannot synchronize anything with a copy.