用c++写读者优先算法

好的，下面是一个简单的C++代码实现读者优先算法（Readers-Writer Locks）。

#include <iostream>
#include <mutex>
#include <condition_variable>

class RWLock {
public:
    RWLock() : readers(0), writers(0) {}

    void ReadLock() {
        std::unique_lock<std::mutex> lock(mtx);
        read_cv.wait(lock, [this] { return writers == 0; });
        ++readers;
    }

    void ReadUnlock() {
        std::unique_lock<std::mutex> lock(mtx);
        --readers;
        if (readers == 0) {
            write_cv.notify_one();
        }
    }

    void WriteLock() {
        std::unique_lock<std::mutex> lock(mtx);
        ++writers;
        write_cv.wait(lock, [this] { return readers == 0 && !writing; });
        writing = true;
    }

    void WriteUnlock() {
        std::unique_lock<std::mutex> lock(mtx);
        --writers;
        writing = false;
        read_cv.notify_all();
        write_cv.notify_one();
    }

private:
    std::mutex mtx;
    std::condition_variable read_cv;
    std::condition_variable write_cv;
    int readers;
    int writers;
    bool writing;
};

int main() {
    RWLock lock;

    // 读者线程
    std::thread reader([&] {
        std::cout << "reader start" << std::endl;
        lock.ReadLock();
        std::cout << "reading" << std::endl;
        lock.ReadUnlock();
        std::cout << "reader end" << std::endl;
    });

    // 写者线程
    std::thread writer([&] {
        std::cout << "writer start" << std::endl;
        lock.WriteLock();
        std::cout << "writing" << std::endl;
        lock.WriteUnlock();
        std::cout << "writer end" << std::endl;
    });

    reader.join();
    writer.join();

    return 0;
}

上述代码使用了C++11的标准库中的`mutex`、`condition_variable`等类，实现了读者优先算法。其中，`ReadLock()`和`ReadUnlock()`分别表示读者加锁和解锁操作，`WriteLock()`和`WriteUnlock()`分别表示写者加锁和解锁操作。在加锁时，读者会等待所有写者完成后才能进行读取，写者则必须等待所有读者完成后才能进行写入。这样，读者和写者之间就可以进行互斥访问了。

当然，这只是一个简单的实现，读者优先算法还有其他更复杂的实现方式，需要根据具体的需求进行选择。