Task.WhenAll for parallel execution in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run two tasks in parallel and wait for both to finish.

C Sharp (C#)

var task1 = Task.Run(() => Console.WriteLine("Task 1"));
var task2 = Task.Run(() => Console.WriteLine("Task 2"));
await [1](task1, task2);

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ATask.WhenAll

BTask.WaitAll

CTask.RunAll

DTask.WaitAny

Attempts:

3 left

💡 Hint

Common Mistakes

Using Task.WaitAll which is synchronous and blocks the thread.

Using Task.WaitAny which waits for only one task to complete.

Task.WhenAll runs multiple tasks in parallel and returns a task that completes when all have finished.

2fill in blank

medium

Complete the code to start three tasks and wait for all to complete using Task.WhenAll.

C Sharp (C#)

var tasks = new List<Task> {
    Task.Run(() => DoWork(1)),
    Task.Run(() => DoWork(2)),
    Task.Run(() => DoWork(3))
};
await [1](tasks);

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ATask.WaitAll

BTask.WhenAll

CTask.RunAll

DTask.WaitAny

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the list to Task.WaitAll which is synchronous.

Using Task.WaitAny which waits for only one task.

Task.WhenAll accepts a collection of tasks and returns a task that completes when all tasks finish.

3fill in blank

hard

Fix the error in the code to correctly wait for multiple tasks to complete asynchronously.

C Sharp (C#)

var taskA = Task.Run(() => Compute(10));
var taskB = Task.Run(() => Compute(20));
Task.WhenAll(taskA, taskB).Wait(); // Fix this line
Console.WriteLine("All tasks done");

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Aawait Task.WhenAny(taskA, taskB);

BTask.WaitAll(taskA, taskB);

CTask.WhenAny(taskA, taskB);

Dawait Task.WhenAll(taskA, taskB);

Attempts:

3 left

💡 Hint

Common Mistakes

Using Task.WaitAll which blocks the thread.

Using Task.WhenAny which waits for only one task.

Using 'await Task.WhenAll' waits asynchronously without blocking the thread, unlike '.Wait()' which blocks.

4fill in blank

hard

Fill both blanks to create a dictionary with task results after all tasks complete.

C Sharp (C#)

var tasks = new List<Task<int>> {
    Task.Run(() => 1),
    Task.Run(() => 2),
    Task.Run(() => 3)
};
var results = await [1](tasks);
var dict = results.[2]((result, index) => new { index, result }).ToDictionary(x => x.index, x => x.result);

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ATask.WhenAll

BSelect

CSelectIndexed

DSelectMany

Attempts:

3 left

💡 Hint

Common Mistakes

Using SelectMany which flattens collections incorrectly.

Using a non-existent method SelectIndexed.

Task.WhenAll waits for all tasks and returns results; Select projects each result with its index.

5fill in blank

hard

Fill in the blanks to run tasks in parallel, filter results greater than 5, and create a list of those results.

C Sharp (C#)

var tasks = new List<Task<int>> {
    Task.Run(() => 3),
    Task.Run(() => 7),
    Task.Run(() => 10)
};
var results = await [1](tasks);
var filtered = results.Where(x => x [2] 5).ToList();
Console.WriteLine(string.Join(", ", filtered));

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ATask.WhenAll

B>

C<

DTask.WaitAll

Attempts:

3 left

💡 Hint

Common Mistakes

Using Task.WaitAll which blocks the thread instead of awaiting.

Using '<' which filters results less than 5.

Task.WhenAll waits for all tasks and returns an array of results; '>' filters results greater than 5.