Windows下使用Interlocked系列函数实现的一个轻量级读写锁

近日在做多窗口渲染的时候（128个directdraw窗口），苦于WIN系统临界区对于多读者情况下的效率问题，窗口绘制速度仅维护在12至18fps之间（设计速度为25fps，机器为i5 450m，集成显卡，4G内存，绘制线程池大小为4，线程池使用的是以下这贴的代码http://blog.youkuaiyun.com/pjchen/archive/2004/11/06/170606.aspx），就萌生了写一个读写锁的念头，在完成之后进行测试，发现虽然仍然达不到设计速度的25fps，但已提升至20至23fps了，在对读写锁进行测试时，发现在最坏的情况下（只有写者，没有读写），锁效率严重低于系统提供的临界区，在一般情况下（读者多于写者，读相对于写频繁），锁效率优于系统提供的临界区。

以下是锁实现代码：

/*! @file ******************************************************************************** 模块名 : 读写锁 文件名 : RWLock.h 文件实现功能 : 实现读者-写者的读写限制，包括读者优先和写者优先 作者 : 郑轩 版本 : 1.0 -------------------------------------------------------------------------------- 备注 : 包含此文件之前，必须直接或间接包含windows.h -------------------------------------------------------------------------------- 修改记录 : 日 期 版本 修改人 修改内容 2010/10/09 1.0 郑轩 新建 *******************************************************************************/ #pragma once class IRWLock { public: virtual DWORD ReadLock(DWORD dwWaitTime = INFINITE)=0; virtual void ReadUnlock()=0; virtual DWORD WriteLock(DWORD dwWaitTime = INFINITE)=0; virtual void WriteUnlock()=0; }; /*! @class ******************************************************************************** 类名称 : CRwLockWithInterlocked 功能 : 用Interlocked系列实现的读写锁 -------------------------------------------------------------------------------- 作者 : 郑轩 *******************************************************************************/ class CRwLockWithInterlocked : public IRWLock { public: CRwLockWithInterlocked(BOOL ReadFirst = TRUE, LONG lMaximumCount = 20) : isReadFirst(ReadFirst), lReadCount(lMaximumCount) { lReadSemaphore = lReadCount; lWriteSemaphore = 1; } virtual ~CRwLockWithInterlocked() { } virtual DWORD ReadLock(DWORD dwWaitTime = INFINITE) { if (dwWaitTime != INFINITE) { DWORD dwStart = GetTickCount(); LONG lCurValue; while(1) { lCurValue = InterlockedDecrement(&lReadSemaphore); if (lCurValue >= 0 && lWriteSemaphore > 0) {//get lock return WAIT_OBJECT_0; } else { InterlockedIncrement(&lReadSemaphore); } if (GetTickCount() - dwStart > dwWaitTime) {//timeout elapse return WAIT_TIMEOUT; } } } else { LONG lCurValue; while(1) { lCurValue = InterlockedDecrement(&lReadSemaphore); if (lCurValue >= 0 && lWriteSemaphore > 0) {//get lock return WAIT_OBJECT_0; } else { InterlockedIncrement(&lReadSemaphore); } } } } virtual void ReadUnlock() { InterlockedIncrement(&lReadSemaphore); } virtual DWORD WriteLock(DWORD dwWaitTime = INFINITE) { LONG lCurValue; if (dwWaitTime != INFINITE) { DWORD dwStart = GetTickCount(); if (isReadFirst == TRUE) {//读优先 while(1) { while(lReadSemaphore < lReadCount) {//等待读队列清空 if (GetTickCount() - dwStart > dwWaitTime) {//timeout elapse return WAIT_TIMEOUT; } } lCurValue = InterlockedDecrement(&lWriteSemaphore); if (lCurValue >= 0) {//占用写信号量 while(lReadSemaphore < lReadCount) {//再次等待读队列清空 if (GetTickCount() - dwStart > dwWaitTime) {//timeout elapse InterlockedIncrement(&lWriteSemaphore); return WAIT_TIMEOUT; } } return WAIT_OBJECT_0; } else { InterlockedIncrement(&lWriteSemaphore); } } } else { while(1) { lCurValue = InterlockedDecrement(&lWriteSemaphore); if (lCurValue >= 0) {//占用写信号量 while(lReadSemaphore < lReadCount) {//等待读队列清空 if (GetTickCount() - dwStart > dwWaitTime) {//timeout elapse InterlockedIncrement(&lWriteSemaphore); return WAIT_TIMEOUT; } } return WAIT_OBJECT_0; } else { InterlockedIncrement(&lWriteSemaphore); } } } } else { if (isReadFirst == TRUE) {//读优先 while(1) { while(lReadSemaphore < lReadCount) {//等待读队列清空 } lCurValue = InterlockedDecrement(&lWriteSemaphore); if (lCurValue >= 0) {//占用写信号量 while(lReadSemaphore < lReadCount) {//再次等待读队列清空 } return WAIT_OBJECT_0; } else { InterlockedIncrement(&lWriteSemaphore); } }//end while 1 } else { while(1) { lCurValue = InterlockedDecrement(&lWriteSemaphore); if (lCurValue >= 0) {//占用写信号量 while(lReadSemaphore < lReadCount) {//等待读队列清空 } return WAIT_OBJECT_0; } else { InterlockedIncrement(&lWriteSemaphore); } }//end while 1 } } } virtual void WriteUnlock() { InterlockedIncrement(&lWriteSemaphore); } private: //屏蔽拷贝构造函数和operator= CRwLockWithInterlocked(const CRwLockWithInterlocked& rhs) : isReadFirst(0), lReadCount(0){}; CRwLockWithInterlocked & operator=(const CRwLockWithInterlocked & rhs){}; const BOOL isReadFirst; const LONG lReadCount; volatile LONG lReadSemaphore, lWriteSemaphore; };  

以下是测试代码：

#include <Windows.h> #include <stdio.h> #include "RWLock.h" IRWLock * gRWLock; LONG RI = 0; LONG WI = 0; DWORD WINAPI gReader(LPVOID lpParam) { for (int i=0; i<100000; i++) { if (gRWLock->ReadLock(10) == WAIT_OBJECT_0) { InterlockedIncrement(&RI); gRWLock->ReadUnlock(); } else { i --; } } return 0; } DWORD WINAPI gWriter(LPVOID lpParam) { for (int i=0; i<100000; i++) { if (gRWLock->WriteLock(10) == WAIT_OBJECT_0) { InterlockedIncrement(&WI); gRWLock->WriteUnlock(); } else { i --; } } return 0; } #define READ_COUNT 4 #define WRITE_COUNT 1 int main() { HANDLE hThread[READ_COUNT+WRITE_COUNT]; gRWLock = new CRwLockWithInterlocked(); DWORD sysTick = GetTickCount(); for (int i=0; i<READ_COUNT; i++) { hThread[i] = CreateThread(NULL, 0, gReader, (LPVOID)i, 0, NULL); } for (int i=0; i<WRITE_COUNT; i++) { hThread[i+READ_COUNT] = CreateThread(NULL, 0, gWriter, (LPVOID)i, 0, NULL); } WaitForMultipleObjects(READ_COUNT+WRITE_COUNT, hThread, TRUE, INFINITE); printf("%dms elapse. RI=%d, WI=%d./n", GetTickCount() - sysTick, RI, WI); return 0; }

在测试中，仅测试了读者优先的情况，使用10ms的定时等待，比无限等待（传入INFINITE）要更有效率。

 

以上代码必有不到之处，欢迎各位指出。