C++ Intel TBB need help with concurrency control

I have a basic websocket server implemented in C++. I'm using Intel TBB's concurrent hash_map to store all the users, uniquely identified by the id. The concurrent hash map will hold a key value pair of <int> and <std::set<string>> where the int is the user's id, and the <std::set<string>> is a set of all instances of the user. For example, the same user user will have the same id say #50, but this user may be connected using multiple devices, such as phone or tablet etc. so the hash_map will look like this hash map: { 50: ["user50_pc", "user50_desktop"]...etc, 51: ["user51_mobile..."] etc } When the set is empty, it must be deleted using the c++ delete keyword, and the key (50 or 51) must be deleted in the hash This is all being executed in concurrently with multiple threads. I've done the code to work for one thread, but I need help getting it to work using multiple threads. Also need performance improvements. Only comment if you used intel tbb before. Thanks