C++11 event loop with thread safe queue

Question

I want to create an event loop class that will run on it's own thread, support adding of tasks as std::functions and execute them. For this, I am using the SafeQueue from here: https://stackoverflow.com/a/16075550/1069662

class EventLoop
{
public:
typedef std::function<void()> Task;

EventLoop(){ stop=false; }

void add_task(Task t) { queue.enqueue(t); }

void start();

void stop() { stop = true; }

private:
    SafeQueue<Task> queue;
    bool stop;
};

void EventLoop::start()
{
    while (!stop) {
        Task t = queue.dequeue(); // Blocking call
        if (!stop) {
            t();
        }
    }    

    cout << "Exit Loop";
}

Then, you would use it like this:

EventLoop loop;
std::thread t(&EventLoop::start, &loop);

loop.add_task(myTask);
// do smth else

loop.stop();
t.join();

My question is: how to stop gracefully the thread ? Here stop cannot exit the loop because of the blocking queue call.

Answer 1

Queue up a 'poison pill' stop task. That unblocks the queue wait and either directly requests the thread to clean up and exit or allows the consumer thread to check a 'stop' boolean.

That's assuming you need to stop the threads/task at all before the app terminates. I usually try to not do that, if I can get away with it.