20 Task Parallel Library Interview Questions and Answers

Task Parallel Library (TPL) is a set of public types and APIs in the System.Threading and System.Threading.Tasks namespaces that provide a managed programming model for coordinating and executing parallel tasks in managed code. TPL scales the degree of concurrency dynamically to most efficiently use all the processors that are available.

If you’re applying for a position that involves parallel programming, you’re likely to be asked questions about your experience with TPL. In this article, we’ll review some common TPL interview questions and how you should answer them.

Task Parallel Library Interview Questions and Answers

Here are 20 commonly asked Task Parallel Library interview questions and answers to prepare you for your interview:

1. What is the Task Parallel Library?

The Task Parallel Library (TPL) is a set of public types and APIs in the System.Threading and System.Threading.Tasks namespaces. The purpose of the TPL is to make it easier for developers to write parallel code.

2. Can you explain what a task factory is in the context of TPL?

A task factory is a class that is responsible for creating and scheduling tasks. In the TPL, a task factory is used to create and schedule tasks that will be executed by a task scheduler. The task factory can be used to customize the behavior of the tasks that it creates, such as setting the priority or specifying a cancellation token.

3. How can we create tasks using the C# Task class?

The C# Task class provides a number of ways to create tasks. The most common way is to use the static Task.Factory.StartNew method, which takes a delegate representing the work to be done as a parameter. Other ways to create tasks include using the Task constructor, or the Task.ContinueWith method.

4. What are some ways to create a continuation and chain tasks together?

One way to create a continuation is to use the Task.ContinueWith() method. This method allows you to specify what action should be taken once the antecedent task has completed. You can also chain tasks together by using the Task.Factory.StartNew() method to create a new task that is dependent on the completion of the previous task.

5. What’s the difference between Wait() and Result()? When would you use one over another?

Wait() will block the current thread until the task is completed, while Result() will return the result of the task once it is completed. You would use Wait() if you need to wait for the task to finish before continuing, while Result() would be used if you don’t need to wait and can just check the task’s status later.

6. What happens when you call Start() on an already running task? Will it throw any exception?

Start() will not throw an exception if the task is already running. However, the task will not restart.

7. What are some important methods provided by the Task class?

The Task class provides a number of methods that are important for working with tasks in the Task Parallel Library. Some of these methods include the following:

– Task.Factory.StartNew: This method is used to create and start a new task.
– Task.WaitAll: This method is used to wait for all tasks in a collection to finish before continuing.
– Task.WaitAny: This method is used to wait for any task in a collection to finish before continuing.
– Task.ContinueWith: This method is used to create a new task that will start after the completion of another task.

8. Is it possible to cancel a task if it’s already been started? If yes, then how?

Yes, it is possible to cancel a task if it has already been started. You can do this by calling the task’s cancel method. This will attempt to stop the task from running. However, it is important to note that there is no guarantee that the task will actually be stopped. If the task is already running, it may ignore the cancel request.

9. What do you understand about thread safe collections and why should they be used for parallel programming?

Thread safe collections are data structures that can be safely accessed by multiple threads simultaneously. This is important for parallel programming because it allows multiple threads to share data without running into race conditions or other problems.

10. What is the importance of the CancellationTokenSource class?

The CancellationTokenSource class is important because it allows you to cancel an asynchronous operation that is based on the Task Parallel Library. This can be useful if you need to stop an operation for some reason, or if you want to make sure that only one operation is running at a time.

11. What are the main parts of a cancellation token?

The main parts of a cancellation token are the source and the token. The source is used to generate the token, and the token is used to pass information about a cancellation request to a task. The source can be any object that implements the ICancellationTokenSource interface, and the token is an object that implements the ICancellationToken interface.

12. What’s the difference between calling Abort() and Stop() on a thread? Which one would you recommend?

Calling Abort() on a thread will immediately terminate the thread, which could leave the program in an unstable state. Calling Stop() on a thread will allow the thread to finish its current task before terminating, which is generally a safer option.

13. What are some best practices that should be followed while working with tasks?

Some best practices for working with tasks include:

– Breaking up tasks into smaller, more manageable pieces
– Prioritizing tasks based on importance and urgency
– Assigning tasks to specific individuals or teams
– Tracking progress on tasks and providing regular updates
– Adjusting tasks as needed based on feedback and new information

14. How does TPL help us achieve better performance when compared to other options like threads, async/await keywords, etc.?

TPL is designed to help us write code that can be executed in parallel across multiple threads, processors, or cores. This can lead to better performance by taking advantage of all available resources. TPL also provides some built-in mechanisms for managing and coordinating these parallel tasks, which can help us avoid some of the potential pitfalls associated with other approaches.

15. When do I need to pass a scheduler to the Task object?

If you need more control over how the task is executed, then you can pass a scheduler to the Task object. This can be useful if you want to ensure that the task is executed on a specific thread or at a specific time.

16. Why should we consider using ContinuationOptions.ExecuteSynchronously whenever possible?

There are a few reasons. First, it can help avoid deadlocks. Second, it can improve performance by avoiding context switches. Finally, it can make your code more predictable and easier to debug.

17. What does ConcurrentQueue.TryDequeue do?

ConcurrentQueue.TryDequeue is a method used to attempt to remove an item from the beginning of a ConcurrentQueue. If the queue is empty, then the method will return false. Otherwise, it will return true and the item will be removed from the queue.

18. What are some common mistakes people make when using TPL?

Some common mistakes people make when using TPL include not using parallelism appropriately, not using data parallelism, and not using task parallelism.

19. What is a synchronization context?

A synchronization context is an object that is used to manage the execution of code on a thread. It is used to ensure that code is executed in a thread-safe manner, and that code blocks are executed in the correct order.

20. What’s the difference between ContinueWith and ContinueWhenAll? Which one should I be using and why?

ContinueWith will execute a task after the current task has completed, while ContinueWhenAll will execute a task after all of the tasks in a given collection have completed. In general, you should use ContinueWith unless you have a specific reason to use ContinueWhenAll.