c++ - Is CRITICAL SECTION required? -

i got code below google search trying learn multithreading. run code critical section used , without critical section, after executing both situations, don't understand why author of code uses critical section.

static unsigned int counter = 100; static bool alive = true; critical_section cs;   static unsigned __stdcall sub(void *args) {     while(alive)     {         entercriticalsection(&cs);         cout << "[sub(" << counter << ")]---" << endl;         counter -= 10;         leavecriticalsection(&cs);         sleep(500);     }      return 0; }  static unsigned __stdcall add(void *args) {     while(alive)     {         entercriticalsection(&cs);         cout << "[add(" << counter << ")]+++" << endl;         counter += 10;         leavecriticalsection(&cs);         sleep(500);     }      return 0; }   int _tmain(int argc, _tchar* argv[]) {     initializecriticalsection(&cs);      unsigned add;     handle hadd = (handle)_beginthreadex(0,0,&add,0,create_suspended, &add);     assert(hadd != 0);      unsigned sub;     handle hsub = (handle)_beginthreadex(0,0,&sub,0,create_suspended, &sub);     assert(hsub != 0);      //start threads     resumethread(hadd);     resumethread(hsub);      //let threads run 10 seconds     sleep(3000);       alive = false;     waitforsingleobject(hsub, infinite);     closehandle(hsub);     waitforsingleobject(hadd, infinite);     closehandle(hadd);      return 0; } 

a critical_section simple sync mechanism multi-threaded. use critical_section protect block of code having 2 or more threads running @ same time.

you not see difference, or without in cases, there protected shared resources getting run on example:

imagine 2 threads accessing resource block of memory @ same time, 1 reading image while other writing image it. reading thread corrupt image.

i suggest more reading on multi-threaded better understand concepts , how use synchronization objects control flow in multi-threaded applications.

1. http://www.codeproject.com/articles/7953/thread-synchronization-for-beginners
2. http://msdn.microsoft.com/en-us/library/windows/desktop/ms681924(v=vs.85).aspx