Catch unhandled exceptions from async

c# .net async-await unhandled-exception
Pieter van Ginkel picture Pieter van Ginkel · Sep 7, 2012 · Viewed 15.6k times · Source

When an async method that is awaited upon throws an exception, the exception is stored somewhere and throwing it is delayed. In a WinForms or WPF application, it uses SynchronizationContext.Current to post throwing of the exception. However, in e.g. a console application, it throws the exception on a thread pool and it brings down the application.

How can I prevent exceptions thrown from an async method from bringing down the application?

EDIT:

Appearantly the issue I'm describing is because I have void async methods. See comments.

Answer

Stephen Cleary picture Stephen Cleary · Sep 7, 2012

How can I prevent exceptions thrown from an async method from bringing down the application?

Follow these best practices:

  1. All async methods should return Task or Task<T> unless they have to return void (e.g., event handlers).
  2. At some point, you should await all Tasks returned from async methods. The only reason you wouldn't want to do this is if you no longer care about the result of the operation (e.g., after you cancel it).
  3. If you need to catch an exception from an async void event handler, then catch it in the event handler - exactly like you would do if this was synchronous code.

You may find my async / await intro post helpful; I cover several other best practices there as well.

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