How to determine that an operation is atomic in the context of multithreading and synchronization?

An operation is considered atomic if it is executed entirely or not at all, without being interrupted or observed in an intermediate state by other threads. In multithreading, this means the operation occurs as a single indivisible action.

For example, incrementing a variable may not be atomic if it is broken into multiple machine instructions. To make an operation atomic, it must be performed using special primitives, such as atomic data types or CPU instructions.

In Swift, atomic operations can be implemented using OSAtomic functions or DispatchQueue for synchronization. Example of atomic increment using DispatchQueue:

let queue = DispatchQueue(label: "atomic.queue")
var counter = 0

func atomicIncrement() {
    queue.sync {
        counter += 1
    }
}

Here, the increment operation is performed inside a synchronized block, making it atomic from the perspective of other threads.