Advanced C++ Programming Cookbook

Understanding what const & mutable mean in the context of multiple threads

In this recipe, we will learn how to deal with objects that are labeled const, but contain std::mutex that must be used to ensure thread synchronization. This recipe is important because it is useful to store std::mutex as a private member of a class, but, as soon as you do this, passing an instance of this object as a constant reference (that is, const &) will result in a compiler error. In this recipe, we will demonstrate why this occurs and how to overcome it.