How to declare volatile variables in Swift

Question

I want to convert to Swift from Objective-C code like following;

int sum = 0;
x = 1;
for (int i = 0; i < 100; i++) {
    sum += x;
}

x is accessible from other threads. So x is declared as a volatile variable.

volatile int x;

How should I write this code in Swift?

Edited

Sorry for my bad pseudo code.

Just I wanted to read the latest value property or field not from thread cache. Java volatile makes that possible. So does Objective-C volatile. ( does it?)

Answer 1

There is currently no equivalent to volatile in Swift.

In Swift you have access to more potent means of expressing global synchronicity of values than the volatile keyword - which does not provide any kind of atomicity guarantees, and must be used with locks to establish critical sections. For example, you might choose locks to synchronize read and write access to a variable. You might choose to use an MVar to indicate that a variable should only have 1 possible valid state across multiple threads.

Or you might choose to simply not express the problem in Swift. If you're looking for the exact behavior of a volatile variable (which, in your situation, sounds unlikely), stick with C and C++.