用增强线程库打印

Question

所以我开始编写一个程序来解析并处理大量的文本。我建立了一个包含以boost线程运行的方法的类。截至目前，每个这些线程都只是打印一些文本语句，然后返回。代码编译和运行没有任何错误。但是，文本不一致地打印出来。这是因为线程并行运行，因此我尝试使用互斥锁来协调输出的使用。但是，我显然做错了，因为输出仍然不一致。为了补充这些，一些输出被打印了两次，这是我无法解释的，因为它没有正确编写互斥锁。下面是我的代码：

/* 
* File: ThreadParser.h 
* Author: Aaron Springut 
* 
* Created on Feburary 2, 2012, 5:13 PM 
*/ 

#ifndef THREADPARSER_H 
#define THREADPARSER_H 

#include <string.h> 
#include <iostream> 
#include <boost/thread/thread.hpp> 
#include <boost/thread/mutex.hpp> 
#include <boost/bind.hpp> 
#include "FileWordCounter.h" 

class ThreadParser { 

    public: 

    ThreadParser(); 
    ThreadParser(std::string fileName); 



    private: 

    //mutex for cout 
    boost::mutex coutMut; 

    std::string dataFile; 
    FileWordCounter fCounter; 

    //threads 
    void parseFile(); 
    void processSearches(); 



}; 

#endif  


/* 
* File: ThreadParser.cpp 
* Author: Aaron Springut 
* 
* Created on Feburary 2, 2012, 5:13 PM 
*/ 


#include "ThreadParser.h" 

using namespace std; 


ThreadParser::ThreadParser(){ 

    double buyNum = 0; 
    buyNum = buyNum * 100; 
    cout << "Percentage of people buying: "<< buyNum <<"%"<<endl; 

} 

ThreadParser::ThreadParser(string fileName){ 

    dataFile = fileName; 
    double buyNum = 0; 

    //create the mutex and aquire a lock on it for this thread 

    boost::mutex::scoped_lock(coutMut); 

    boost::thread parseThread(boost::bind(&ThreadParser::parseFile, this)); 
    boost::thread processSearches(boost::bind(&ThreadParser::processSearches,this)); 

    buyNum = buyNum * 100; 
    cout << "Percentage of people buying: "<< buyNum <<"%"<<endl; 


} 


void ThreadParser::parseFile(){ 

    boost::mutex::scoped_lock(coutMut); 
    cout << "parseFileThreadLaunch"<<endl; 
    return; 

} 


void ThreadParser::processSearches(){ 

    boost::mutex::scoped_lock(coutMut); 
    cout << "processSearchesLaunch"<<endl; 
    return; 

} 

至于什么错误，这里是来自运行此程序两个输出的一个例子：

Percentage of people buying: parseFileThreadLaunch 
processSearchesLaunch 
0% 

好吧，COUT不是线程安全的，我已经做了互斥体出现问题。

Percentage of people buying: parseFileThreadLaunch 
0% 
processSearchesLaunch 
processSearchesLaunch 

这很混乱，最后一行怎么打印两次？这是cout不是线程安全的结果吗？或者，我是否缺少更大图片的一部分。

编辑： 类是被称为像这样的主要功能：

string fileName("AOLData.txt"); 
cout << fileName<< endl; 

ThreadParser tp(fileName); 

Answer 1

boost::mutex::scoped_lock(coutMut); 

这不会做你认为它。这会创建一个临时的，立即销毁，释放锁定。就像int(3);。

你想：

boost::mutex::scoped_lock sl(moutMut); 

这将创建一个对象，sl，直到它超出范围是持有锁。