Task and TaskGroup in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Understanding TaskGroup concurrency behavior

Consider this Swift code using TaskGroup. What will be printed first?

iOS Swift

func testTaskGroup() async {
  await withTaskGroup(of: String.self) { group in
    group.addTask { "First" }
    group.addTask { "Second" }
    for await result in group {
      print(result)
      break
    }
  }
  print("Done")
}

Task {
  await testTaskGroup()
}

A Done\nSecond

B Second\nDone

C Done\nFirst

D First\nDone

💡 Hint

The first completed task result is printed before breaking the loop.

The for await loop prints the first completed task's result, which is "First" here, then breaks. After the group ends, "Done" is printed.

❓ lifecycle

intermediate

Task cancellation inside TaskGroup

What happens if a task inside a TaskGroup calls Task.cancel() on itself?

iOS Swift

func cancelInsideGroup() async {
  await withTaskGroup(of: Void.self) { group in
    group.addTask {
      Task.cancel()
      print("Cancelled")
    }
    group.addTask {
      print("Running")
    }
  }
}

Task {
  await cancelInsideGroup()
}

A Prints "Cancelled" and "Running"

B Prints only "Running"

C Prints only "Cancelled"

D No output, tasks are cancelled immediately

💡 Hint

Cancellation does not stop the current task immediately.

Calling Task.cancel() marks the task as cancelled but does not stop execution immediately, so "Cancelled" is printed. The other task runs normally.

📝 Syntax

advanced

Correct syntax for adding tasks in TaskGroup

Which option correctly adds a task returning an Int in a TaskGroup?

iOS Swift

func addTaskExample() async {
  await withTaskGroup(of: Int.self) { group in
    // Add a task here
  }
}

A group.addTask { 42 }

B group.addTask { return 42 }

C group.addTask { await 42 }

D group.addTask { async { 42 } }

💡 Hint

The closure can return the value directly without return keyword.

Option A is correct because the closure returns 42 directly. Option A is valid Swift but redundant here. Option A is invalid because 'await' is not needed for a literal. Option A is invalid syntax.

🔧 Debug

advanced

Why does this TaskGroup code deadlock?

Given this code, why does it deadlock?

iOS Swift

func deadlockExample() async {
  await withTaskGroup(of: Void.self) { group in
    group.addTask {
      await deadlockExample() // recursive call
    }
  }
}

Task {
  await deadlockExample()
}

A Because the task is not awaited properly

B Because the recursive call waits for the group to finish, causing a cycle

C Because TaskGroup does not support recursion

D Because the group is empty and never completes

💡 Hint

Think about waiting inside the group for itself to finish.

The recursive call awaits the same TaskGroup to finish, causing a deadlock cycle where the group waits on itself.

🧠 Conceptual

expert

TaskGroup result ordering guarantee

Which statement about the order of results from withTaskGroup is true?

A Results are returned in the order tasks were added

B Results are returned in random order each run

C Results are returned in the order tasks complete

D Results are returned sorted by their value

💡 Hint

Think about concurrency and task completion timing.

TaskGroup yields results as tasks complete, so order depends on completion, not addition order.