什么是C++中的读写锁？

#include <iostream>
#include <shared_mutex>
#include <thread>
#include <vector>

class Data {
private:
    int value;
    mutable std::shared_mutex mutex;

public:
    Data() : value(0) {}

    // 读操作
    int getValue() const {
        std::shared_lock<std::shared_mutex> lock(mutex);
        return value;
    }

    // 写操作
    void setValue(int newValue) {
        std::unique_lock<std::shared_mutex> lock(mutex);
        value = newValue;
    }
};

void reader(Data& data, int id) {
    for (int i = 0; i < 5; ++i) {
        int value = data.getValue();
        std::cout << "Reader " << id << " got value: " << value << std::endl;
        std::this_thread::sleep_for(std::chrono::milliseconds(100));
    }
}

void writer(Data& data, int id) {
    for (int i = 0; i < 3; ++i) {
        data.setValue(i);
        std::cout << "Writer " << id << " set value to: " << i << std::endl;
        std::this_thread::sleep_for(std::chrono::milliseconds(100));
    }
}

int main() {
    Data data;
    std::vector<std::thread> threads;

    for (int i = 0; i < 3; ++i) {
        threads.emplace_back(reader, std::ref(data), i);
    }

    for (int i = 0; i < 2; ++i) {
        threads.emplace_back(writer, std::ref(data), i);
    }

    for (auto& thread : threads) {
        thread.join();
    }

    return 0;
}