Question

Is there convention regarding whenever method which is essentially read-only, but has mutex/ lock which may need to be modified, is const or not?

if there is not one, what would be disadvantage/bad design if such method is const

Thank you

Answer 1

You can mark data members with the keyword mutable to allow them to be modified in a constant member function, e.g.:

struct foo 
{
    mutable mutex foo_mutex;
    // ....
    void bar() const
    {
        auto_locker lock(foo_mutex);
        // ...
    }
};

Try to do this as little as possible because abusing mutable is evil.