Qt 5 to-do in QtConcurrent

class ThreadEngineBarrier
{
private:
    // The thread count is maintained as an integer in the count atomic
    // variable. The count can be either positive or negative - a negative
    // count signals that a thread is waiting on the barrier.

    // BC note: inlined code from Qt < 4.6 will expect to find the QMutex 
    // and QAtomicInt here. ### Qt 5: remove.
    QMutex mutex;
    QAtomicInt count;