Under C# is Int64 use on a 32 bit processor dangerous

Question

I read in the MS documentation that assigning a 64-bit value on a 32-bit Intel computer is not an atomic operation; that is, the operation is not thread safe. This means tha

Answer 1

Even if the writes were atomic, chances are you would still need to take out a lock whenever you accessed the variable. If you didn't do that, you'd at least have to make the variable volatile to make sure that all threads saw the new value the next time they read the variable (which is almost always what you want). That lets you do atomic, volatile sets - but as soon as you want to do anything more interesting, such as adding 5 to it, you'd be back to locking.

Lock free programming is very, very hard to get right. You need to know exactly what you're doing, and keep the complexity to as small a piece of code as possible. Personally, I rarely even try to attempt it other than for very well known patterns such as using a static initializer to initialize a collection and then reading from the collection without locking.

Using the Interlocked class can help in some situations, but it's almost always a lot easier to just take out a lock. Uncontested locks are "pretty cheap" (admittedly they get expensive with more cores, but so does everything) - don't mess around with lock-free code until you've got good evidence that it's actually going to make a significant difference.