Question

Is the mutex used in method GetValues() released before or after copy constructing the dummy instance?

class Protect
{};

class Test
{
public:
    Protect GetValues() const;

private:
    Protect m_protVal;
    Mutex m_mutex;
};

Protect Test::GetValues() const
{
    CLockGuard lock(m_mutex);

    return m_protVal;
}

int main(int argc, char** argv)
{
    Test myTestInstance;

    Protect dummy = myTestInstance.GetValues();
}

Let’s assume CLockGuard and Mutex are standard classes provided with boost lib.

Answer 1

Yes:-). Formally, there are two “copies” when returning a
value: one to some special place used to actually return the value, and
the second after the return, to wherever the value must be finally
placed. Either or both can be optimized out, however. The destruction
of local variables occurs after the first, but before the second. (NRVO
and RVO may lead to the first being optimized out, but they don’t affect
your code, since you’re not returning a local variable.)