Regarding question on volatile

[yugandhargv]

Hi all,
I know to you what is the exact usage of volatile in a program .I heard that when you declare a variable as volatile it tells the compiler not to do optimization. I want to know exactly in what situations we can use volatile can anyone help me out.

[myrdos]

Volatile is mainly useful in multi-threaded programs. It tells the compiler to immediately assign values to a variable. Say you have this:

int myVar = 3;

sleep(3);
myVar = 6;
sleep(3);
myVar = 8;

The optimizer says, hey, let's skip the busy work and just set myVar to 8. It changes your code to:

int myVar;
sleep(3);
sleep(3);
myVar = 8;

But if another thread is running, and waiting to see the variable change to 6, it will never happen and your program won't run as expected.

You use volatile when two threads are accessing the same variable, but only one of them is changing it. If both threads are changing the variable, volatile is not enough, and you need to use mutexes or some other synchronization mechanism.