Question

int i=5;
f()
{
    i++;
    i--;
}

For the above code if three threads execute the above function f() simultanously then what can be the total different values of global variable i are possible?

Note : i is initialized to 5 globaly.

Answer 1

I would say that’s an exercise in combinatorics, which I’m personally not going to do, however I do want to make clear that this is NOT the correct way to have threads execute this f(). The problem is that the implementation of operator++ is not a single instruction, which means that halfway through one call to operator++ it could context switch and do another f() in another thread. This would then lead to corrupt state of your variable i.

So determining the possible values of i without proper synchronization is useless, since it could be any number of values, real or unreal, as things might go corrupt.