c++ - C/C++ 中的并发日志文件访问

Question

我正在创建一个多线程程序，多个线程可能需要调用一个全局函数

writeLog(const char* pMsg);

并且 writeLog 将实现类似 tihs 的东西:

void writeLog(const char* pMsg)
{
   CRITICAL_SECTION cs;

   // initialize critical section
   ...

   EnterCriticalSection(&cs);

   // g_pLogFilePath is a global variable.
   FILE *file;
   if (0!=fopen_s(&file, g_pLogFilePath, "r+"))  
      return;

   fprintf(file, pMsg);

   fclose(file):
   LeaveCriticalSection(&cs);
}

我的问题是:

1) is it the best way to do concurrent logging? i.e., using critical section.

2) since I will write log in many places in the threads, 
and since each log writing will involve open/close file,
does the io will impact the performance significantly?

谢谢!

Answer 1

进行并发日志记录的最佳方法是使用 existing log library for C++ 之一.它们具有许多您可能会喜欢使用的特性(不同的附加程序、格式、并发性等)。

如果您仍然想拥有自己的解决方案，您可能会有这样的事情:初始化一次并保持状态(文件处理程序和互斥锁)的简单单例

class Log
{
public:

    // Singleton
    static Log & getLog() 
    {
        static Log theLog;
        return theLog;
    }

    void log(const std::string & message)
    {
         // synchronous writing here
    }
private:
    // Hidden ctor
    Log()
    {
         // open file ONCE here
    }

    // Synchronisation primitive - instance variable
    // CRITICAL_SECTION or Boost mutex (preferable)
    CRITICAL_SECTION cs_;

    // File handler: FILE * or std::ofstream
    FILE * handler_;
};