Question

When I suspect a Task‘s Action had failed I used to just sit waiting for the AggregateExceptionto finally get thrown so I could dig into the InnerException. Recently, however, I noticed that by attempting to resize the form which had initiated the failing Task I could force the error to throw visibly.

Two questions:

1. Is there a better way to do this? (I hate the “Wrap the call in an try/catch/re-throw and put a break point on the re-throw technique).
2. I thought the AggregateException got thrown when the Task object itself is garbage collected. Is that true?
3. In light of the answer to #2: Why does resizing trigger the AggregateException more immediately?

Answer 1

Is there a better way to do this?

You can either use the Result property or the Wait() function. Both block and if the Task fails, they throw the AggregateException. Another option, if you want to do something with the exception, is to use ContinueWith() with TaskContinuationOptions.OnlyOnFaulted.

I thought the AggregateException got thrown when the Task object itself is garbage collected. Is that true?

Yes, if the Exception of the Task is not accessed in any way, it will throw the exception when it’s finalized on .Net 4.0. (.Net 4.5 changes that, unhandled exceptions from Tasks no longer throw when the Task is finalized.)

In light of the answer to #2: Why does resizing trigger the AggregateException more immediately?

Most likely because it creates some objects, which causes the garbage collection to run.