Task for launching concurrent work in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift concurrency code?

Consider the following Swift code using Task to run concurrent work. What will be printed?

Swift

import Foundation

func fetchData() async -> String {
    return "Data fetched"
}

Task {
    let result = await fetchData()
    print(result)
}

print("Task launched")

A Data fetched\nTask launched

B Task launched

C Data fetched

D Task launched\nData fetched

💡 Hint

Remember that Task runs asynchronously and the main thread continues immediately.

The Task runs asynchronously, so print("Task launched") executes first. Then the async function completes and prints Data fetched.

❓ Predict Output

intermediate

What does this Swift Task code print?

Analyze this Swift code snippet using Task and sleep. What is the output?

Swift

import Foundation

Task {
    print("Start")
    try? await Task.sleep(nanoseconds: 1_000_000_000)
    print("End")
}

print("After Task")

A After Task\nStart\nEnd

B Start\nEnd\nAfter Task

C Start\nAfter Task\nEnd

D After Task

💡 Hint

The Task runs asynchronously, so the main thread prints before the task finishes.

The main thread prints After Task immediately. The Task prints Start, waits 1 second, then prints End.

🔧 Debug

advanced

Why does this Swift Task code cause a runtime error?

Examine this Swift code that launches a Task. It crashes at runtime. What is the cause?

Swift

import Foundation

var value = 0

Task {
    value += 1
    print(value)
}

print(value)

A The variable <code>value</code> is accessed concurrently without synchronization, causing a data race.

B The variable <code>value</code> is immutable and cannot be changed inside the <code>Task</code>.

C The <code>Task</code> must be awaited, otherwise it causes a runtime error.

D The <code>print(value)</code> outside the <code>Task</code> causes a syntax error.

💡 Hint

Think about shared variable access in concurrent code.

Accessing and modifying value from multiple threads without synchronization causes a data race, which can crash the program.

📝 Syntax

advanced

Which option correctly launches a detached Swift Task?

Choose the correct syntax to launch a detached Task that runs concurrently without inheriting the current context.

A

Task {
    print("Detached task running")
}.detached()

B

Task.detached {
    print("Detached task running")
}

C

Task.runDetached {
    print("Detached task running")
}

D

Task.detach {
    print("Detached task running")
}

💡 Hint

Look for the official method name to create a detached task.

The correct method is Task.detached. Other options are invalid syntax or methods.

🚀 Application

expert

How many concurrent tasks are launched and what is the final output?

Consider this Swift code that launches multiple tasks. How many tasks run concurrently and what is printed?

Swift

import Foundation

for i in 1...3 {
    Task.detached {
        print("Task \(i) started")
        try? await Task.sleep(nanoseconds: 500_000_000)
        print("Task \(i) finished")
    }
}

print("All tasks launched")

A 3 tasks run concurrently; output is "All tasks launched" only, because tasks run in background and don't print.

B 1 task runs at a time; output is "Task 1 started", "Task 1 finished", then "Task 2 started", etc., ending with "All tasks launched".

C 3 tasks run concurrently; output starts with "All tasks launched" followed by each task's start and finish messages in any order.

D No tasks run because <code>Task.detached</code> is invalid; output is only "All tasks launched".

💡 Hint

Detached tasks run concurrently and the main thread continues immediately.

Three detached tasks run concurrently. The main thread prints "All tasks launched" immediately. Task prints may appear in any order due to concurrency.