Question

Say we have two threads, one is reading a bool in a loop and another can toggle it at certain times. Personally I think this should be atomic because sizeof(bool) in C++ is 1 byte and you don’t read/write bytes partially but I want to be 100% sure.

So yes or no?

EDIT:

Also for future reference, does the same apply to int?

Answer 1

It all depends on what you actually mean by the word “atomic”.

Do you mean “the final value will be updated in one go” (yes, on x86 that’s definitely guaranteed for a byte value – and any correctly aligned value up to 64 bits at least), or “if I set this to true (or false), no other thread will read a different value after I’ve set it” (that’s not quite such a certainty – you need a “lock” prefix to guarantee that).