Windows在Vista 和 Server2008以后才开始提供读写锁API,即SRW系列函数(InitializeSRWLock,AcquireSRWLockShared,AcquireSRWLockExclusive等)。
网上也有很多读写锁实现，基本上都是用互斥量对象和信号量对象实现。但是对于读写锁这种特殊的锁（锁住时间短）自旋的方式等待应该更合适，用Interlocked系列函数实现读写锁纯粹是因为闲的，也没有做过性能方面的测试，此实现是写优先的，如果不设计成写优先，写很难竞争到锁，是不合理的。。。
下面是源码：

#pragma once

///////////////////////////
class rwlock
{
public:
    rwlock();

    void r_lock();

    void r_unlock();

    void w_lock();

    void w_unlock();
private:
    //写锁
    volatile long wlocks;
    //写等待
    volatile long wwaits;
    //读锁
    volatile long rlocks;
};

//////////////////////////
class rlock
{
public:
    rlock(rwlock& lock);
    ~rlock();

private:
    rwlock& _lock;
};

//////////////////////////
class wlock
{
public:
    wlock(rwlock& lock);
    ~wlock();

private:
    rwlock& _lock;
};

#include "rwlock.h"
#include <Windows.h>

rwlock::rwlock()
    : wlocks(0)
    , rlocks(0)
    , wwaits(0)
{
}

void rwlock::r_lock()
{
    //当前有写等待则不能进入读  写优先
    while (InterlockedCompareExchange(&wwaits, 0, 0) != 0) {
        Sleep(1);
    }

    //等待写释放
    while (InterlockedExchange(&wlocks, 1) != 0) {
        Sleep(1);
    }
    //读++
    InterlockedIncrement(&rlocks);

    //写释放
    InterlockedExchange(&wlocks, 0);
}

void rwlock::r_unlock()
{
    InterlockedDecrement(&rlocks);
}

void rwlock::w_lock()
{
    if (InterlockedExchange(&wlocks, 1) != 0) {
        //写等待++
        InterlockedIncrement(&wwaits);
        
        //等待写
        while (InterlockedExchange(&wlocks, 1) != 0) {
            Sleep(1);
        }
        
        //写等待--
        InterlockedDecrement(&wwaits);
    }

    //等待读释放
    while (InterlockedCompareExchange(&rlocks, 0, 0) != 0) {
        Sleep(1);
    }
}

void rwlock::w_unlock()
{
    //写释放
    InterlockedExchange(&wlocks, 0);
}

//////////////////////////////////////
rlock::rlock(rwlock & lock)
    :_lock(lock)
{
    _lock.r_lock();
}

rlock::~rlock()
{
    _lock.r_unlock();
}

//////////////////////////////////////
wlock::wlock(rwlock & lock)
    :_lock(lock)
{
    _lock.w_lock();
}

wlock::~wlock()
{
    _lock.w_unlock();
}