【转】单例模式 C++实现 多线程安全

转自：http://blog.csdn.net/joanlynnlove/article/details/7462254

项目中需要在多线程环境下，输出日志到标准输出，以下是实现过程。

首先，我们需要一个锁类，能够自动初始化，并且降低耦合。

/*
 * locker.h
 *
 *  Created on: Apr 14, 2012
 *      Author: joan
 */

#ifndef LOCKER_H_
#define LOCKER_H_

#include "../OPTION.h"

class locker
{
public:
    inline locker(){        pthread_mutex_init(&mutex,NULL);}
    inline ~locker(){       pthread_mutex_destroy(&mutex);}
    inline void lock(){     pthread_mutex_lock(&mutex);}
    inline void unlock(){   pthread_mutex_unlock(&mutex);}
private:
    pthread_mutex_t mutex;
};

#endif /* LOCKER_H_ */

其次，声明日志类，重点是将构造函数私有化，将函数成员和数据成员声明为静态，添加实例指针和全局访问点。

/*
 * log.h
 *
 *  Created on: Apr 8, 2012
 *      Author: joan
 */

#ifndef LOG_H_
#define LOG_H_

#include "../OPTION.h"
#include "locker.h"

/*
 * this class is responsible for the running log of tinyJSE
 * there should only exist one instance of tinyLog,
 * so we use singleton to implement tinyLog
 */
class tinyLog
{
public:
    static tinyLog *GetInstance();
    static void WriteLog(const char *FORMAT,...);
private:
    tinyLog();
    ~tinyLog();
private:
        static tinyLog *log;
static locker llock;
};
#endif /* LOG_H_ */

然后是日志类的实现，注意全局访问点中使用double check提高性能。

/*
 * log.cpp
 *
 *  Created on: Apr 8, 2012
 *      Author: joan
 */

#include "../OPTION.h"
#include "log.h"

tinyLog * tinyLog::log = NULL;
locker tinyLog::llock;

tinyLog::tinyLog()
{
}

tinyLog::~tinyLog()
{
}

/*
 * get the pointer to the only instance of tinyLog
 * use double check to assure only one instance is created
 */
tinyLog *tinyLog::GetInstance()
{
    if(NULL == log)
    {//double check
        llock.lock();
        if(NULL == log)
        {
            log = new tinyLog();
        }
        llock.unlock();
    }
    return log;
}

/*
 * Unified handling of the log of tinyJSE
 */
void tinyLog::WriteLog(const char *FORMAT,...)
{
    va_list args;

    va_start(args, FORMAT);

    llock.lock();

    vfprintf(stdout,FORMAT,args);

    llock.unlock();

    va_end(args);

}

使用该单例：

#define PRINT(FORMAT,args...)   tinyLog::GetInstance()->WriteLog(FORMAT,##args)