Safe and effective way to put a mutex on a container entry

Question

C++\'s std::mutex does not have a move constructor. There is a good reason for that. Basically, move constructors themselves are not generally thread safe, and

Answer 1

The mutex does not require to be moved:

Imagine that every row in your map is like:

template <class T>
class row
{
    shared_ptr<mutex> m;
    T data;
    ...
};

So if your row need to be moved or copied, there is no problem.

Then, you may access the mutex from every process to access the data.

Of course, you need a global mutex to perform changes on the whole map: insert / delete / [] / any other operation that change the state of the map.

EDITED:

Following a simple example of code with a mutex in every row. (It does not implement anything else that just the data structure)

#include <memory>
#include <map>
#include <mutex>

template <class T>
class row
{
    std::shared_ptr<std::mutex> m;
    T data;
public:
    row( std::shared_ptr<std::mutex> mut): m(mut){};
};

auto main () -> int
{
    std::shared_ptr<std::mutex> mut(new std::mutex);
    std::map<int,row<int>> db;
    row<int> a(mut);
    db.insert(std::pair<int, row<int>>(1, a));
    return 0;
}