C / C++ / MFC

int v = 5;
int volatile m = 3;
int i;
for(i = 0; i < 10; i++) {
  if(v == 5) { break; }
}
for(i = 0; i < 10; i++) {
  if(m == 3) { break; }
}

1311006  add         byte ptr [eax],al 
	int i;
	for(i = 0; i < 10; i++)
	{  
		if(v == 5)
		{
			break;
		}
	}

	for(i = 0; i < 10; i++)
01311008  xor         eax,eax 
0131100A  lea         ebx,[ebx] 
	{ 
		if(m == 3)
01311010  mov         ecx,dword ptr [esp] 
01311013  cmp         ecx,ecx 
01311015  je          main+1Dh (131101Dh) 
01311017  inc         eax  
01311018  cmp         eax,0Ah 
0131101B  jl          main+10h (1311010h) 
		{
			break;
		}
	}
}

Critical Data = 1 // Maxwell: Thread-2 made it before the 3 sec timeout of waiting for Thread-1's.
Success

volatile bool Sentinel = true;
int CriticalData = 0;

unsigned ThreadFunc1( void* pArguments ) {
   while (Sentinel) { // Maxwell: This thread keeps watching this variable all the time.
      Sleep(0);
   }
   cout << "Critical Data = " << CriticalData << endl;
   return 0; // Maxwell: Note that this thread never ends unless someone change value of Sentinel.
} 

unsigned  ThreadFunc2( void* pArguments ) {
   Sleep(2000); // Maxwell: Note that this thread ends in "2" seconds.
   CriticalData++; // Maxwell: Make the value from 0 to 1. 
                   //  Then this thread ends Thread-1's loop in next line, 
                   //  to guarantee that Thread-1 will see this value changed while the loop ends.
   Sentinel = false; // Maxwell: This line is trying to end the loop of Thread-1.
   return 0;
}

int main() {
   HANDLE hThread1, hThread2; 
   DWORD retCode;

   hThread1 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)&ThreadFunc1,
      NULL, 0, NULL);
   hThread2 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)&ThreadFunc2,
      NULL, 0, NULL);

   if (hThread1 == NULL || hThread2 == NULL)       {
      cout << "CreateThread failed." << endl; 
      return 1;
   }

   retCode = WaitForSingleObject(hThread1,3000); // Maxwell: Wait Thread-1 with maximal 3 sec timeout.

   CloseHandle(hThread1);
   CloseHandle(hThread2);

   if (retCode == WAIT_OBJECT_0 && CriticalData == 1 )
      cout << "Success" << endl; // Thread-2 made it by changing value of CriticalData to "1" !!
   else
      cout << "Failure" << endl;
}

while (Sentinel)
{
   Sleep(0);
}

George_George wrote:

Sleep(0) will wait until there is a signal.

George_George wrote:

Then I am confused what is the original purpose of the MSDN sample? It advise people to put volatile keyword to all shared variables between multiple threads -- or else function may be broken?

George_George wrote:

1. In your experience, when do you use volatile?

George_George wrote:

If we share data between threads and we are already using synchronization approach like mutex, do we need to add additional volatile keyword?

George_George wrote:

and can be omitted.