How do I find elements with custom comparators with std::unordered_map in multithreaded code?

To find elements in an `std::unordered_map` using custom comparators in a multithreaded C++ application, you first need to ensure that your custom comparator can effectively hash the keys and handle thread safety. Below is an example that demonstrates how you can set up a custom comparator with `std::unordered_map` and safely access its elements under multithreaded conditions.

c++, unordered_map, custom comparators, multithreaded programming, thread safety, hashing

This example illustrates using custom hash functions and comparators with `std::unordered_map` in a multithreaded environment in C++.


        #include <iostream>
        #include <unordered_map>
        #include <string>
        #include <shared_mutex>
        #include <thread>

        struct CustomHash {
            std::size_t operator()(const std::string& key) const {
                return std::hash<:string>()(key);
            }
        };

        struct CustomEqual {
            bool operator()(const std::string& lhs, const std::string& rhs) const {
                return lhs == rhs;
            }
        };

        class ThreadSafeMap {
        private:
            std::unordered_map<:string int customhash customequal> map_;
            mutable std::shared_mutex mutex_;
        
        public:
            void insert(const std::string& key, int value) {
                std::unique_lock lock(mutex_);
                map_[key] = value;
            }

            bool find(const std::string& key, int& value) {
                std::shared_lock lock(mutex_);
                auto it = map_.find(key);
                if (it != map_.end()) {
                    value = it->second;
                    return true;
                }
                return false;
            }
        };

        void exampleUsage() {
            ThreadSafeMap ts_map;

            // Inserting elements
            ts_map.insert("key1", 1);
            ts_map.insert("key2", 2);

            // Finding elements
            int value;
            if (ts_map.find("key1", value)) {
                std::cout << "Found key1: " << value << std::endl;
            }
        }

        int main() {
            std::thread t1(exampleUsage);
            std::thread t2(exampleUsage);
            t1.join();
            t2.join();

            return 0;
        }

How do I find elements with custom comparators with std::unordered_map in multithreaded code?

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How do I find elements with custom comparators with std::unordered_map in multithreaded code?

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