> The important thing to remember is that each of these cannot be split into separate instructions.
Nitpick, but they absolutely can be split into several instructions, and this is the most common way it’s implemented on RISClike processors, and also single instructions aren’t necessarily atomic.
The actual guarantee is that the entire operation (load, store, RMW, whatever) occurs in one “go” and no other thread can perform an operation on that variable during this atomic operation (it can’t write into the low byte of your variable as you read it).
It’s probably best euphemismed by imagining that every atomic operation is just the normal operation wrapped in a mutex, but implemented in a much more efficient manner. Of course, with large enough types, Atomic variables may well be implemented via a mutex
Nitpick, but they absolutely can be split into several instructions, and this is the most common way it’s implemented on RISClike processors, and also single instructions aren’t necessarily atomic.
The actual guarantee is that the entire operation (load, store, RMW, whatever) occurs in one “go” and no other thread can perform an operation on that variable during this atomic operation (it can’t write into the low byte of your variable as you read it).
It’s probably best euphemismed by imagining that every atomic operation is just the normal operation wrapped in a mutex, but implemented in a much more efficient manner. Of course, with large enough types, Atomic variables may well be implemented via a mutex