The decimal type problem in financial word

Decimal is a typical type used in financial word, to prevent lost of information/precision during mathematical computations. There is one issue that is not put in a consideration. The C# ECMA specification guarantees that the following types will be written atomically: reference types, bool, char, byte, sbyte, short, ushort, uint, int and float. There is no decimal on that list. It means that:

class AtomicityExample {
    decimal _value;
    void SetValue(decimal value) {_value = value;}
    decimal GetValue() {return _value;}
}

If the code is executed by many threads, the returned value of GetValue method may be not a value that was set by a SetValue.

What is even less know is that the order of the operations in C# may change, due to .net optimization. Consider following code:

class OrderExample {
    decimal d1;
    volatile decimal d2;
    decimal d3;

    void Assign(){
        d1 = 1;
        d2 = 2;
        d3 = 3;
    }
}

The assignment in a code above can happen in following ways:

d1 = 1;
d2 = 2;
d3 = 3;

or

d1 = 1;
d3 = 3;
d2 = 2;

or

d3 = 3;
d1 = 1;
d2 = 2;

In other words volatile variable can be assigned only after d1 was assigned, but when exactly depends on a compiler. Be aware that majority of programmers don't even use volatile keyword, and without volatile keyword reads/writes of variables above can happen in any order. And it matters, because I've seen so many times a code that looked like:

class FalseSecurityExample {
    decimal d1;
    bool assigned;

    void Assign(){
        d1 = 1;
        assigned = true;
    }

    decimal Calculate(){
        if(assigned){
            return d1;
        }
    }
}

It means that in an example above d1 may not be set before it is returned, and if you add to a consideration fact that decimal is not atomic, you can expect anything to be returned by this code.

When I ask people why do they write such code, and if they are aware of issues that are illustrated above, usually they answer, that we are not writing a project for NASA, or anything like that so bug off. Interesting.