Question

I have a little problem with a C++ class…
I have a private member bool clientConnected.
and a getter bool isClientConnected() {return clientConnected;}

now the proble is.. that clientConnected is set from a different thread.

in main I have a loop

while (!x.isClientConnected())
{}

now if I compile it in Debug config.
All works fine… while exits as soon as clientConnected is set to true.
but if I compile it in Release config.
The compiler optimizes the loop as its constant.
and makes the following:

00141C01  cmp         al,bl  
00141C03  je          SDL_main+0A1h (141C01h)  

the value of al is never updated again.
so its always thinks its false.
I tried also with volatile, same results

how can I prevent this optimization in class so the value will get updated on each call, without having to write something like

bool z = x.isClientConnected();
while (!z) { z = x.isClientConnected(); }

Answer 1

volatile http://msdn.microsoft.com/en-us/library/12a04hfd(v=vs.80).aspx looks like simple answer to your problem:

“Objects declared as volatile are not used in certain optimizations because their values can change at any time.”

volatile bool clientConnected;
bool isClientConnected() const volatile {return clientConnected;}

---

But – you have loop taking CPU:

while (!x.isClientConnected())
{}

Better is to wait on semaphore:

x.waitForConnected();
void X::waitForConnected()
{
   WaitForSingleObject(m_connectedSemaphore, ,....);
}

How to create/use semaphore in MS Windows see: http://msdn.microsoft.com/en-us/library/windows/desktop/ms686946(v=vs.85).aspx