Linux平台用C++封装线程读写锁

Linux平台用C++封装线程读写锁

    在Linux平台上已经有现成的线程读写锁pthread_rwlock_t以及相关API，现将这些API封装成与Win32平台上相同的接口，以便于编写跨平台程序。这些API包括pthread_rwlock_init，pthread_rwlock_rdlock，pthread_rwlock_tryrdlock，pthread_rwlock_wrlock，pthread_rwlock_trywrlock，pthread_rwlock_unlock，pthread_rwlock_destroy，可在Linux在线手册上查阅它们的说明。下边的代码在VS2005中编辑，在Fedora 13虚拟机中编译，测试通过。

RWLockImpl.h

#ifndef _RWLockImpl_Header
#define _RWLockImpl_Header

#include <iostream>
#include <pthread.h>
#include <errno.h>
#include <assert.h>

using namespace std;

/*
 读写锁允许当前的多个读用户访问保护资源，但只允许一个写读者访问保护资源
*/

//-----------------------------------------------------------------
class CRWLockImpl
{
protected:
    CRWLockImpl();
    ~CRWLockImpl();
    void ReadLockImpl();
    bool TryReadLockImpl();
    void WriteLockImpl();
    bool TryWriteLockImpl();
    void UnlockImpl();

private:
    pthread_rwlock_t m_rwl;
};

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

class CMyRWLock: private CRWLockImpl
{
public:

    //创建读/写锁
    CMyRWLock(){};

    //销毁读/写锁
    ~CMyRWLock(){};

    //获取读锁
    //如果其它一个线程占有写锁，则当前线程必须等待写锁被释放，才能对保护资源进行访问
    void ReadLock();

    //尝试获取一个读锁
    //如果获取成功，则立即返回true，否则当另一个线程占有写锁，则返回false
    bool TryReadLock();

    //获取写锁
    //如果一个或更多线程占有读锁，则必须等待所有锁被释放
    //如果相同的一个线程已经占有一个读锁或写锁，则返回结果不确定
    void WriteLock();

    //尝试获取一个写锁
    //如果获取成功，则立即返回true，否则当一个或更多其它线程占有读锁，返回false
    //如果相同的一个线程已经占有一个读锁或写锁，则返回结果不确定
    bool TryWriteLock();

    //释放一个读锁或写锁
    void Unlock();

private:
    CMyRWLock(const CMyRWLock&);
    CMyRWLock& operator = (const CMyRWLock&);
};

inline void CMyRWLock::ReadLock()
{
    ReadLockImpl();
}

inline bool CMyRWLock::TryReadLock()
{
    return TryReadLockImpl();
}

inline void CMyRWLock::WriteLock()
{
    WriteLockImpl();
}

inline bool CMyRWLock::TryWriteLock()
{
    return TryWriteLockImpl();
}

inline void CMyRWLock::Unlock()
{
    UnlockImpl();
}

#endif

RWLockImpl.cpp

#include "RWLockImpl.h"

CRWLockImpl::CRWLockImpl()
{
    if (pthread_rwlock_init(&m_rwl, NULL))
        cout<<"cannot create reader/writer lock"<<endl;
}

CRWLockImpl::~CRWLockImpl()
{
    pthread_rwlock_destroy(&m_rwl);
}

void CRWLockImpl::ReadLockImpl()
{
    if (pthread_rwlock_rdlock(&m_rwl))
        cout<<"cannot lock reader/writer lock"<<endl;
}

bool CRWLockImpl::TryReadLockImpl()
{
    int rc = pthread_rwlock_tryrdlock(&m_rwl);
    if (rc == 0)
        return true;
    else if (rc == EBUSY)
        return false;
    else
        cout<<"cannot lock reader/writer lock"<<endl;

    return false;
}

void CRWLockImpl::WriteLockImpl()
{
    if (pthread_rwlock_wrlock(&m_rwl))
        cout<<"cannot lock reader/writer lock"<<endl;
}

bool CRWLockImpl::TryWriteLockImpl()
{
    int rc = pthread_rwlock_trywrlock(&m_rwl);
    if (rc == 0)
        return true;
    else if (rc == EBUSY)
        return false;
    else
        cout<<"cannot lock reader/writer lock"<<endl;
    return false;
}

void CRWLockImpl::UnlockImpl()
{
    if (pthread_rwlock_unlock(&m_rwl))
        cout<<"cannot unlock reader/writer lock"<<endl;
}

    下边是测试代码

// pthread_rwlock.cpp : 定义控制台应用程序的入口点。
//

#include "RWLockImpl.h"

//创建一个读写锁对象
CMyRWLock g_myRWLock;
volatile int g_counter = 0;

//线程函数
void * StartThread(void *pParam)
{
    int lastCount = 0;
    for (int i = 0; i < 10000; ++i)
    {
        g_myRWLock.ReadLock();
        lastCount = g_counter;
        //在读锁域，两个线程不断循环交替访问全局变量g_counter
        for (int k = 0; k < 100; ++k)
        {
            if (g_counter != lastCount)
                cout<<"the value of g_counter has been updated."<<endl;
            sleep(0);
        }
        g_myRWLock.Unlock();


        g_myRWLock.WriteLock();
        //在写锁域，只有一个线程可以修改全局变量g_counter的值
        for (int k = 0; k < 100; ++k)
        {
            --g_counter;
            sleep(0);
        }
        for (int k = 0; k < 100; ++k)
        {
            ++g_counter;
            sleep(0);
        }
        ++g_counter;
        if (g_counter <= lastCount)
            cout<<"the value of g_counter is error."<<endl;
        g_myRWLock.Unlock();
    }

    return (void *)0;
}

int main(int argc, char* argv[])
{
    pthread_t thread1,thread2;
    pthread_attr_t attr1,attr2;

    //创建两个工作线程
    pthread_attr_init(&attr1);
    pthread_attr_setdetachstate(&attr1,PTHREAD_CREATE_JOINABLE);
    if (pthread_create(&thread1,&attr1, StartThread,0) == -1)
    {
        cout<<"Thread 1: create failed"<<endl;
    }
    pthread_attr_init(&attr2);
    pthread_attr_setdetachstate(&attr2,PTHREAD_CREATE_JOINABLE);
    if (pthread_create(&thread2,&attr2, StartThread,0) == -1)
    {
        cout<<"Thread 2: create failed"<<endl;
    }

    //等待线程结束
    void *result;
    pthread_join(thread1,&result);
    pthread_join(thread2,&result);

    //关闭线程，释放资源
    pthread_attr_destroy(&attr1);
    pthread_attr_destroy(&attr2);

    cout<<"the g_counter = "<<g_counter<<endl;

    int iWait;
    cin>>iWait;

    return 0;
}

   编译，运行
  

    运行结果与在Win32下用C++实现多线程读写锁的相同。

    欢迎转载，麻烦带上链接：http://blog.csdn.net/chexlong/article/details/7163233，谢谢合作！