iOS Concurrency with GCD & Operations

Sep 12 2023 · Swift 5.8, macOS 13, iOS 16, Xcode 14.3

Part 2: Concurrency Problems & Solutions

14. Challenge: Make Number Class Thread-Safe

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Challenge: Make Number Class Thread-safe

In the previous exercise, you used a private concurrent queue and dispatch barrier to create a thread-safe version of the Person class. In this challenge, you’ll create a thread-safe version of a Number class. Open the NumberChanger project in the starter folder. Build and run it to see its output is jumbled, like the Person names were. Turn on TSan to confirm the race condition.

let isolationQueue = DispatchQueue(
  label: "com.kodeco.number.isolation",
  attributes: .concurrent)
isolationQueue.async(flags: .barrier) {
  self.value = value
  randomDelay(0.5) = name
isolationQueue.sync {
  "\(self.value) :: \("
Current number: 2 :: two
Current number: 2 :: two
Current number: 3 :: three
Current number: 4 :: four
Current number: 5 :: five
Current number: 6 :: six
Final number: 6 :: six