[swift-users] Bool type and reading and writing operation atomicity

[Dale Myers]

Put simply, are reading and writing to Bools both atomic operations in Swift (3)?

Obviously, something reading and then assigning assuming the value doesn't change between is not correct, but would something like the following be fine: 

    var myBool = false

    // Thread 1
    while true {
        if randomEvent() {
            myBool = true
        }
    }
    
    // Thread 2
    while true {
        if myBool {
            print("Was set to true")
        } else {
            print("Not set")
        }
    }


I understand that in thread 2, the value of myBool can change between the check and the print statements, but that's fine. What I want to confirm for my team is that `myBool` can never be in some weird "third" state? 

>From what I can tell, behind the scenes, Bool uses a Builtin.Int1 for storage. I can't find the definition for this type anywhere so I can't check what it is really doing. My assumption is that it uses something like a C++ unsigned char behind the scenes, which would be fine with the above code on x86 and ARM as far as I'm aware. 

Can someone help me figure out if I'm right or wrong in my assumptions?

Thanks,

Dale