（转）互斥对象锁和临界区锁性能比较 .

在Win32平台上进行多线程编程，常会用到锁。下边用C++实现了互斥对象（Mutex）锁和临界区（CRITICAL_SECTION）锁，以加深理解和今后方便使用。代码已在VS2005环境下编译测试通过。

Lock.h

#ifndef _Lock_H
#define _Lock_H

#include <windows.h>


//锁接口类
class ILock
{
public:
virtual ~ILock() {}

virtual void Lock() const = 0;
virtual void Unlock() const = 0;
};

//互斥对象锁类
class Mutex : public ILock
{
public:
Mutex();
~Mutex();

virtual void Lock() const;
virtual void Unlock() const;

private:
HANDLE m_mutex;
};

//临界区锁类
class CriSection : public ILock
{
public:
CriSection();
~CriSection();

virtual void Lock() const;
virtual void Unlock() const;

private:
CRITICAL_SECTION m_critclSection;
};


//锁
class CMyLock
{
public:
CMyLock(const ILock&);
~CMyLock();

private:
const ILock& m_lock;
};


#endif

#ifndef _Lock_H #define _Lock_H #include <windows.h> //锁接口类 class ILock { public: virtual ~ILock() {} virtual void Lock() const = 0; virtual void Unlock() const = 0; }; //互斥对象锁类 class Mutex : public ILock { public: Mutex(); ~Mutex(); virtual void Lock() const; virtual void Unlock() const; private: HANDLE m_mutex; }; //临界区锁类 class CriSection : public ILock { public: CriSection(); ~CriSection(); virtual void Lock() const; virtual void Unlock() const; private: CRITICAL_SECTION m_critclSection; }; //锁 class CMyLock { public: CMyLock(const ILock&); ~CMyLock(); private: const ILock& m_lock; }; #endif

Lock.cpp

#include "Lock.h"

//---------------------------------------------------------------------------

//创建一个匿名互斥对象
Mutex::Mutex()
{
m_mutex = ::CreateMutex(NULL, FALSE, NULL);
}

//销毁互斥对象，释放资源
Mutex::~Mutex()
{
::CloseHandle(m_mutex);
}

//确保拥有互斥对象的线程对被保护资源的独自访问
void Mutex::Lock() const
{
DWORD d = WaitForSingleObject(m_mutex, INFINITE);
}

//释放当前线程拥有的互斥对象，以使其它线程可以拥有互斥对象，对被保护资源进行访问
void Mutex::Unlock() const
{
::ReleaseMutex(m_mutex);
}

//---------------------------------------------------------------------------

//初始化临界资源对象
CriSection::CriSection()
{
::InitializeCriticalSection(&m_critclSection);
}

//释放临界资源对象
CriSection::~CriSection()
{
::DeleteCriticalSection(&m_critclSection);
}

//进入临界区，加锁
void CriSection::Lock() const
{
::EnterCriticalSection((LPCRITICAL_SECTION)&m_critclSection);
}

//离开临界区，解锁
void CriSection::Unlock() const
{
::LeaveCriticalSection((LPCRITICAL_SECTION)&m_critclSection);
}

//---------------------------------------------------------------------------

//利用C++特性，进行自动加锁
CMyLock::CMyLock(const ILock& m) : m_lock(m)
{
m_lock.Lock();
}

//利用C++特性，进行自动解锁
CMyLock::~CMyLock()
{
m_lock.Unlock();
}

#include "Lock.h" //--------------------------------------------------------------------------- //创建一个匿名互斥对象 Mutex::Mutex() { m_mutex = ::CreateMutex(NULL, FALSE, NULL); } //销毁互斥对象，释放资源 Mutex::~Mutex() { ::CloseHandle(m_mutex); } //确保拥有互斥对象的线程对被保护资源的独自访问 void Mutex::Lock() const { DWORD d = WaitForSingleObject(m_mutex, INFINITE); } //释放当前线程拥有的互斥对象，以使其它线程可以拥有互斥对象，对被保护资源进行访问 void Mutex::Unlock() const { ::ReleaseMutex(m_mutex); } //--------------------------------------------------------------------------- //初始化临界资源对象 CriSection::CriSection() { ::InitializeCriticalSection(&m_critclSection); } //释放临界资源对象 CriSection::~CriSection() { ::DeleteCriticalSection(&m_critclSection); } //进入临界区，加锁 void CriSection::Lock() const { ::EnterCriticalSection((LPCRITICAL_SECTION)&m_critclSection); } //离开临界区，解锁 void CriSection::Unlock() const { ::LeaveCriticalSection((LPCRITICAL_SECTION)&m_critclSection); } //--------------------------------------------------------------------------- //利用C++特性，进行自动加锁 CMyLock::CMyLock(const ILock& m) : m_lock(m) { m_lock.Lock(); } //利用C++特性，进行自动解锁 CMyLock::~CMyLock() { m_lock.Unlock(); }

    下边是测试代码

// MyLock.cpp : 定义控制台应用程序的入口点。
//

#include <iostream>
#include <process.h>
#include <time.h>
#include "Lock.h"

using namespace std;


#define ENABLE_MUTEX
#define ENABLE_CRITICAL_SECTION


#if defined (ENABLE_MUTEX)

//创建一个互斥对象类型锁
Mutex g_Lock;

#elif defined (ENABLE_CRITICAL_SECTION)

//创建一个临界区类型锁
CriSection g_Lock;

#endif


void LockCompare(int &iNum)
{
CMyLock lock1(g_Lock);

iNum++;
}


//线程函数
unsigned int __stdcall StartThread(void *pParam)
{
char *pMsg = (char *)pParam;
if (!pMsg)
{
return (unsigned int)1;
}

CMyLock lock2(g_Lock);

clock_t tStart,tEnd;

tStart = clock();

int iNum = 0;
for (int i = 0; i < 100000; i++)
{
LockCompare(iNum);
}

tEnd = clock();
#if defined (ENABLE_MUTEX)

cout<<"The lock type is mutex, time = "<<(tEnd - tStart)<<" ms."<<endl;

#elif defined (ENABLE_CRITICAL_SECTION)

cout<<"The lock type is critical section, time = "<<(tEnd - tStart)<<" ms."<<endl;

#endif

return (unsigned int)0;
}

int main(int argc, char* argv[])
{
HANDLE hThread1, hThread2;
unsigned int uiThreadId1, uiThreadId2;

char *pMsg1 = "First print thread.";
char *pMsg2 = "Second print thread.";

//创建两个工作线程，分别打印不同的消息
hThread1 = (HANDLE)_beginthreadex(NULL, 0, &StartThread, (void *)pMsg1, 0, &uiThreadId1);
hThread2 = (HANDLE)_beginthreadex(NULL, 0, &StartThread, (void *)pMsg2, 0, &uiThreadId2);

//等待线程结束
DWORD dwRet = WaitForSingleObject(hThread1,INFINITE);
if ( dwRet == WAIT_TIMEOUT )
{
TerminateThread(hThread1,0);
}
dwRet = WaitForSingleObject(hThread2,INFINITE);
if ( dwRet == WAIT_TIMEOUT )
{
TerminateThread(hThread2,0);
}

//关闭线程句柄，释放资源
::CloseHandle(hThread1);
::CloseHandle(hThread2);

system("pause");
return 0;
}

// MyLock.cpp : 定义控制台应用程序的入口点。 // #include <iostream> #include <process.h> #include <time.h> #include "Lock.h" using namespace std; #define ENABLE_MUTEX #define ENABLE_CRITICAL_SECTION #if defined (ENABLE_MUTEX) //创建一个互斥对象类型锁 Mutex g_Lock; #elif defined (ENABLE_CRITICAL_SECTION) //创建一个临界区类型锁 CriSection g_Lock; #endif void LockCompare(int &iNum) { CMyLock lock1(g_Lock); iNum++; } //线程函数 unsigned int __stdcall StartThread(void *pParam) { char *pMsg = (char *)pParam; if (!pMsg) { return (unsigned int)1; } CMyLock lock2(g_Lock); clock_t tStart,tEnd; tStart = clock(); int iNum = 0; for (int i = 0; i < 100000; i++) { LockCompare(iNum); } tEnd = clock(); #if defined (ENABLE_MUTEX) cout<<"The lock type is mutex, time = "<<(tEnd - tStart)<<" ms."<<endl; #elif defined (ENABLE_CRITICAL_SECTION) cout<<"The lock type is critical section, time = "<<(tEnd - tStart)<<" ms."<<endl; #endif return (unsigned int)0; } int main(int argc, char* argv[]) { HANDLE hThread1, hThread2; unsigned int uiThreadId1, uiThreadId2; char *pMsg1 = "First print thread."; char *pMsg2 = "Second print thread."; //创建两个工作线程，分别打印不同的消息 hThread1 = (HANDLE)_beginthreadex(NULL, 0, &StartThread, (void *)pMsg1, 0, &uiThreadId1); hThread2 = (HANDLE)_beginthreadex(NULL, 0, &StartThread, (void *)pMsg2, 0, &uiThreadId2); //等待线程结束 DWORD dwRet = WaitForSingleObject(hThread1,INFINITE); if ( dwRet == WAIT_TIMEOUT ) { TerminateThread(hThread1,0); } dwRet = WaitForSingleObject(hThread2,INFINITE); if ( dwRet == WAIT_TIMEOUT ) { TerminateThread(hThread2,0); } //关闭线程句柄，释放资源 ::CloseHandle(hThread1); ::CloseHandle(hThread2); system("pause"); return 0; }

    在线程函数StartThread中，循环100000次，对保护资源“iNum ”反复加锁，解锁。编译，运行5次，将每次打印的线程锁切换耗时时间记录下来。之后，将测试代码中的宏 #define ENABLE_MUTEX 注释掉，禁掉互斥锁，启用临界区锁，重新编译代码，运行5次。下边是分别是互斥锁和临界区锁耗时记录（不同机器上耗时会不同）：

 

互斥锁

线程Id	耗时 / ms					总计
1	141	125	125	125	125	641
2	140	125	140	125	156	686

 

临界区锁

线程Id	耗时 / ms					总计
1	15	16	31	31	31	124
2	31	31	31	16	31	140

 

    互斥锁总共耗时：641+686=1327 ms，而临界区锁：124+140=264 ms。显而易见，临界区锁耗时比互斥锁耗时节约了大概5倍的时间。

    总结：1、在同一个进程的多线程同步锁，宜用临界区锁，它比较节约线程上下文切换带来的系统开销。但因临界区工作在用户模式下，所以不能对不同进程中的多线程进行同步。2、因互斥对象锁属于内核对象，所以在进行多线程同步时速度会比较慢，但是可以在不同进程的多个线程之间进行同步。

 转自：http://blog.csdn.net/chexlong/article/details/7060425