Task groups for parallel execution in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a task group in Swift.

Swift

try await [1](of: Int.self) { group in
    // parallel tasks here
}

Drag options to blanks, or click blank then click option'

Agroup

BwithGroup

CwithTaskGroup

DtaskGroup

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'group' or 'taskGroup' which are not valid Swift concurrency methods.

Confusing 'withGroup' with the correct 'withTaskGroup'.

The correct method to start a task group in Swift concurrency is 'withTaskGroup'.

2fill in blank

medium

Complete the code to add a child task inside a task group.

Swift

try await withTaskGroup(of: Int.self) { group in
    group.[1] {
        return 42
    }
}

Drag options to blanks, or click blank then click option'

Aadd

BaddTask

Cspawn

Dasync

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'async' which is a keyword, not a method here.

Using 'spawn' which is not a Swift concurrency method.

The method to add a child task to a task group is 'addTask'.

3fill in blank

hard

Fix the error in the code to await results from all child tasks in the group.

Swift

try await withTaskGroup(of: Int.self) { group in
    group.addTask {
        return 10
    }
    var sum = 0
    for await result in group.[1] {
        let value = try result.get()
        sum += value
    }
    return sum
}

Drag options to blanks, or click blank then click option'

Aresults

Bvalues

Call

Dawait

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'values' which is not a property of TaskGroup.

Using 'await' as a property which is a keyword.

The correct property to iterate over all child task results is 'results'.

4fill in blank

hard

Fill both blanks to create a task group that returns the first completed child task result.

Swift

try await withTaskGroup(of: Int.self) { group in
    group.[1] {
        return 5
    }
    group.[2] {
        return 10
    }
    for await result in group.results {
        return try result.get()
    }
}

Drag options to blanks, or click blank then click option'

Aadd

Bspawn

CaddTask

Dasync

Attempts:

3 left

💡 Hint

Common Mistakes

Using different methods for adding tasks.

Using 'spawn' or 'async' which are invalid here.

Both child tasks are added using 'addTask' method to the task group.

5fill in blank

hard

Fill all three blanks to create a task group that sums only even results from child tasks.

Swift

try await withTaskGroup(of: Int.self) { group in
    group.[1] {
        return 3
    }
    group.[2] {
        return 4
    }
    var total = 0
    for await result in group.[3] {
        let number = try result.get()
        if number % 2 == 0 {
            total += number
        }
    }
    return total
}

Drag options to blanks, or click blank then click option'

AaddTask

Badd

Cresults

Dvalues

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'add' instead of 'addTask' to add child tasks.

Using 'values' instead of 'results' to iterate results.

Child tasks are added with 'addTask' and results are iterated using 'results'.

Practice

1. What is the main purpose of using a TaskGroup in Swift concurrency?

easy

A. To run multiple tasks in parallel and wait for all to complete

B. To create a single long-running task

C. To pause the current task indefinitely

D. To handle errors in synchronous code

Solution

1. Step 1: Understand what TaskGroup does

   A TaskGroup lets you run many tasks at the same time, managing them together.

2. Step 2: Identify the main use

   It allows parallel execution and waits until all tasks finish before continuing.

3. Final Answer:

   To run multiple tasks in parallel and wait for all to complete -> Option A

4. Quick Check:

   TaskGroup = parallel tasks + wait [OK]

Hint: TaskGroup runs tasks together and waits for all [OK]

Common Mistakes:

• Thinking TaskGroup runs only one task
• Confusing TaskGroup with error handling
• Assuming TaskGroup pauses tasks

2. Which of the following is the correct way to add a task inside a TaskGroup in Swift?

easy

A. group.runTask(fetchData())

B. group.createTask(fetchData)

C. group.addTask { await fetchData() }

D. group.startTask { fetchData() }

Solution

1. Step 1: Recall the method to add tasks

   The correct method to add a task is addTask with a closure.

2. Step 2: Check syntax correctness

   group.addTask { await fetchData() } uses group.addTask { await fetchData() }, which is the right syntax.

3. Final Answer:

   group.addTask { await fetchData() } -> Option C

4. Quick Check:

   Use addTask with closure [OK]

Hint: Use addTask with closure to add work [OK]

Common Mistakes:

• Using wrong method names like runTask or createTask
• Not using closure syntax
• Omitting await inside the task

3. What will be the output of this Swift code using a TaskGroup?

func fetchNumber(_ n: Int) async -> Int {
    return n * 2
}

func runGroup() async {
    await withTaskGroup(of: Int.self) { group in
        for i in 1...3 {
            group.addTask { await fetchNumber(i) }
        }
        var results = [Int]()
        for await result in group {
            results.append(result)
        }
        print(results.sorted())
    }
}

Task {
    await runGroup()
}

medium

A. Compilation error

B. [1, 2, 3]

C. [6, 4, 2]

D. [2, 4, 6]

Solution

1. Step 1: Understand the task group adds tasks for numbers 1 to 3

   Each task returns the input number multiplied by 2: 2, 4, and 6.

2. Step 2: Collect results and sort them before printing

   Results are collected in any order but sorted before printing, so output is [2, 4, 6].

3. Final Answer:

   [2, 4, 6] -> Option D

4. Quick Check:

   Results doubled and sorted = [2,4,6] [OK]

Hint: Remember to sort results after parallel tasks [OK]

Common Mistakes:

• Assuming results print in order added
• Forgetting to await inside addTask
• Confusing output with original numbers

4. Identify the error in this Swift code using a TaskGroup:

await withTaskGroup(of: Int.self) { group in
    for i in 1...3 {
        group.addTask { fetchNumber(i) }
    }
    for await result in group {
        print(result)
    }
}

Assuming fetchNumber is an async function.

medium

A. Missing await inside addTask closure

B. Cannot use for await with TaskGroup

C. TaskGroup must be declared with var

D. fetchNumber must return Void

Solution

1. Step 1: Check how fetchNumber is called inside addTask

   fetchNumber is async, so it must be awaited inside the closure.

2. Step 2: Identify missing await keyword

   The closure calls fetchNumber(i) without await, causing a compile error.

3. Final Answer:

   Missing await inside addTask closure -> Option A

4. Quick Check:

   Async calls inside addTask need await [OK]

Hint: Always await async calls inside addTask closures [OK]

Common Mistakes:

• Forgetting await inside addTask
• Thinking for await can't be used with TaskGroup
• Declaring TaskGroup incorrectly

5. You want to fetch data from multiple URLs in parallel using a TaskGroup and collect only the successful results (non-nil). Which approach correctly filters out nil results while running tasks in parallel?

hard

A. Run tasks sequentially inside the group to avoid nil results

B. Add tasks returning optional data, then filter non-nil in for await loop

C. Use addTask with throwing function and catch errors outside group

D. Use withThrowingTaskGroup but ignore errors and collect all results

Solution

1. Step 1: Understand the goal to run tasks in parallel and filter nil

   Running tasks in parallel with TaskGroup allows concurrency; filtering nil after collecting results is straightforward.

2. Step 2: Evaluate options for filtering nil results

   Add tasks returning optional data, then filter non-nil in for await loop correctly adds tasks returning optional data and filters non-nil results in the for await loop, matching the goal.

3. Final Answer:

   Add tasks returning optional data, then filter non-nil in for await loop -> Option B

4. Quick Check:

   Filter nil after parallel tasks with for await [OK]

Hint: Filter nil results after collecting parallel task outputs [OK]

Common Mistakes:

• Trying to run tasks sequentially losing parallelism
• Ignoring errors without filtering nil
• Misusing throwing task groups for simple filtering