Question

I am creating a multiple threads program and several threads may need to call a global function

writeLog(const char* pMsg);

and the writeLog will be implemented something like tihs:

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);
}

My questions are:

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?

Thanks!

Answer 1

A CS is a reasonable way to protect the logging, yes. To avoid inflicting the open/write/close upon every call from every thread, it’s common to queue off the string, (if not already malloced/newed, you may need to copy it), to a separate log thread. Blocking disk delays are then buffered from the logging calls. Any lazy-writing etc. optimizations can be implemented in the log thread.

Alternatively, as suggested by the other posters, just use a logging framework that has all this stuff already implemented.