c++实现读写锁

1.源码实现

#include <iostream>
#include <vector>
#include <string>
#include <thread>
#include <mutex>

using namespace std;

class RWLock {
public:
    RWLock() : rcnt(0){}
    ~RWLock(){}

    void rlock()
    {
        rmtx.lock();

        if(++rcnt == 1)
        {
            wmtx.lock();
        }

        rmtx.unlock();
    }

    void runlock()
    {
        rmtx.lock();

        if(--rcnt == 0)
        {
            wmtx.unlock();
        }

        rmtx.unlock();
    }

    void wlock()
    {
        wmtx.lock();
    }

    void wunlock()
    {
        wmtx.unlock();
    }

private:
    mutex rmtx;
    mutex wmtx;
    int rcnt;
};

volatile int var = 10;
RWLock rwLock;
mutex showLock;

void Write()
{
    rwLock.wlock();
    var += 10;
    showLock.lock();
    cout << "write var: " << var << endl;
    showLock.unlock();
    rwLock.wunlock();
}

void Read()
{
    rwLock.rlock();
    showLock.lock();
    cout << "read var: " << var << endl;
    showLock.unlock();
    rwLock.runlock();
}

int main()
{
    vector<thread> writers;
    vector<thread> readers;

    for(int i=0; i<10; i++)
    {
        writers.push_back(thread(Write));
    }

    for(int i=0; i<20; i++)
    {
        readers.push_back(thread(Read));
    }

    for(auto &t : writers)
    {
        t.join();
    }

    for(auto &t : readers)
    {
        t.join();
    }

    return 0;
}

2.编译源码

$ g++ -o example example.cpp -lpthread -std=c++11

3.运行及其结果

$ ./example
write var: 20
write var: 30
write var: 40
write var: 50
write var: 60
write var: 70
write var: 80
read var: 80
read var: 80
read var: 80
read var: 80
write var: 90
read var: 90
read var: 90
read var: 90
read var: 90
read var: 90
read var: 90
read var: 90
read var: 90
read var: 90
read var: 90
read var: 90
read var: 90
read var: 90
read var: 90
read var: 90
read var: 90
write var: 100
write var: 110