Question

In a multithreaded C++ program, I have the equivalent of this running in one thread:

while(obj->member) { } // waiting for obj->member to be set to false in another thread

and in another thread, obj->member is set to false. Even when it’s set to false, however, the loop doesn’t break. If I change it to this:

while(obj->member) { Sleep(1) }

It works as expected and breaks when obj->member is set to false in the other thread.
Why does it work like this?

Answer 1

Try making member volatile. This will force it to be fetched from memory each time it is used, rather than from a CPU register (which is how the compiler might optimise it.)