What is the best way to catch exception in Task?

by

There are two ways you can do this, dependent on the version of the language you are using.

C# 5.0 and above

You can use the async and await keywords to simplify a great deal of this for you.

async and await were introduced into the language to simplify using the Task Parallel Library, preventing you from having to use ContinueWith and allowing you to continue to program in a top-down manner.

Because of this, you can simply use a try/catch block to catch the exception, like so:

try
{
    // Start the task.
    var task = Task.Factory.StartNew<StateObject>(() => { /* action */ });

    // Await the task.
    await task;
}
catch (Exception e)
{
    // Perform cleanup here.
}

Note that the method encapsulating the above must use have the async keyword applied so you can use await.

C# 4.0 and below

You can handle exceptions using the ContinueWith overload that takes a value from the TaskContinuationOptions enumeration, like so:

// Get the task.
var task = Task.Factory.StartNew<StateObject>(() => { /* action */ });

// For error handling.
task.ContinueWith(t => { /* error handling */ }, context,
    TaskContinuationOptions.OnlyOnFaulted);

The OnlyOnFaulted member of the TaskContinuationOptions enumeration indicates that the continuation should only be executed if the antecedent task threw an exception.

Of course, you can have more than one call to ContinueWith off the same antecedent, handling the non-exceptional case:

// Get the task.
var task = new Task<StateObject>(() => { /* action */ });

// For error handling.
task.ContinueWith(t => { /* error handling */ }, context, 
    TaskContinuationOptions.OnlyOnFaulted);

// If it succeeded.
task.ContinueWith(t => { /* on success */ }, context,
    TaskContinuationOptions.OnlyOnRanToCompletion);

// Run task.
task.Start();

More Related Contents:

  1. Asynchronously wait for Task to complete with timeout
  2. How to cancel Task await after a timeout period
  3. Running multiple async tasks and waiting for them all to complete
  4. StaTaskScheduler and STA thread message pumping
  5. Why should I prefer single ‘await Task.WhenAll’ over multiple awaits?
  6. Is it considered acceptable to not call Dispose() on a TPL Task object?
  7. Best way in .NET to manage queue of tasks on a separate (single) thread
  8. Synchronously waiting for an async operation, and why does Wait() freeze the program here
  9. How to use non-thread-safe async/await APIs and patterns with ASP.NET Web API?
  10. Multiple Parallel.ForEach loops in .Net
  11. How to put a task to sleep (or delay) in C# 4.0?
  12. Simplest way to do a fire and forget method in c# 4.0
  13. What is the use for Task.FromResult in C#
  14. Create a completed Task
  15. Waiting for async/await inside a task
  16. Revisiting Task.ConfigureAwait(continueOnCapturedContext: false)
  17. If my interface must return Task what is the best way to have a no-operation implementation?
  18. multiple awaits vs Task.WaitAll – equivalent?
  19. Can .NET Task instances go out of scope during run?
  20. Executing tasks in parallel
  21. Difference between returning and awaiting a Task in an async method [duplicate]
  22. Use Task.Run() in synchronous method to avoid deadlock waiting on async method?
  23. A pattern for self-cancelling and restarting task
  24. How to correctly write Parallel.For with async methods
  25. Using CancellationToken for timeout in Task.Run does not work [duplicate]
  26. Converting async/await to Task.ContinueWith
  27. Correct way to delay the start of a Task
  28. Best way to limit the number of active Tasks running via the Parallel Task Library
  29. Task chaining (wait for the previous task to completed)
  30. Create a completed Task

Leave a Comment