#include <mutex>
#include <condition_variable>
#include <deque>


class SpScQueue
{
    std::mutex mutex;
    std::deque<int> queue;
    bool closed = false;
    std::condition_variable cond;
public:
    void push(int x)
    {
        std::lock_guard<std::mutex> lock{mutex};
        queue.push_back(x);
        cond.notify_one();
    }
    void close()
    {
        std::lock_guard<std::mutex> lock{mutex};
        closed = true;
        cond.notify_all();
        /*
         * Important: The lock guard's destructor will unlock the mutex.
         * As per C++ 32.6.4.2.2 Class mutex [thread.mutex.class] paragraph 2,
         * is is valid for another thread (in this case the consumer) to destroy
         * the mutex before the unlock() returns.
         * Users have to make sure not to access any members after unlocking,
         * for example by moving the notify_all() out of the lock
         */
    }
    // return false if closed and empty
    bool pop(int* out)
    {
        std::unique_lock<std::mutex> lock{mutex};
        while(queue.empty() && ! closed)
            cond.wait(lock);
        if(queue.empty())
            return false;
        *out = queue.front();
        queue.pop_front();
        return true;
    }
};

// producer borrows queue
void producer(SpScQueue* queue)
{
    for(int i = 0; i < 10; ++i)
        queue->push(i);
    queue->close();
}
// consumer holds ownership of queue
void consumer(std::unique_ptr<SpScQueue>&& queue)
{
    int x;
    while(queue->pop(&x)) {
        // consume value x
    }
    queue.reset(); // delete queue
}