Psychic Debugging of Async Methods

re: Psychic Debugging of Async Methods

Stephen Toub - MSFT — Wed, 30 Jan 2013 19:19:57 GMT

@Chris Charabaruk: I agree this kind of functionality would be useful, and as mentioned it's something we're looking into. It would be difficult to do well in a VS Update, however, as doing this in a robust manner requires the runtime to track more information than it currently does.

@James Chaldecott: I'm glad you're enjoying the posts; thanks for the kind words. Regarding a custom awaiter, yes, you could certainly implement one, e.g. its OnCompleted method could add the Task to a ConcurrentDictionary<Task,WhateverStateYouWantedTracked>, and then pass along to the underlying OnCompleted method a delegate that removes the task and invokes the actual continuation, e.g. task.GetAwaiter().OnCompleted(() => { m_awaitedTasks.TryRemove(task, ...); continuation(); });

re: Psychic Debugging of Async Methods

James Chaldecott — Wed, 30 Jan 2013 09:25:58 GMT

Thanks for the info, Stephen. At least I know it's not worth looking for how I might write such an extension, now. I hope it's something you'll be able to work on soon.

I suppose if I *really* wanted something it might be possible to write an extension method a bit like ConfigureAwait that added entries into a list & removed them when the continuation runs (perhaps using CallerFilePath, etc). Does that sound possible?

Anyway, I also forgot to say what Jerome said: Another excellent post! I really appreciate all the in-depth information you provide in your posts. Thanks!

re: Psychic Debugging of Async Methods

Chris Charabaruk — Wed, 30 Jan 2013 04:00:59 GMT

@Stephen: It'd certainly be handy to add await tracking to the debugger! Given how much of a move there is to working with asynchronous functions in the .NET 4.5 / WinRT age, being able to know the state of those functions is becoming more and more important. I hope that you guys decide to introduce it in VS2012 Update 3 (I figure it's probably a bit late to get something that big into Update 2 at this point).

re: Psychic Debugging of Async Methods

Stephen Toub - MSFT — Tue, 29 Jan 2013 17:53:30 GMT

@Damien: Thanks. I'm half surprised any of this even compiles, given that I just typed it directly into the blogging tool ;) I've fixed the typo.

@James: That information isn't currently tracked in any way that would be easily mineable. We're thinking about it for the future.

@Jerome: I'm glad you found it helpful.

re: Psychic Debugging of Async Methods

Jerome — Tue, 29 Jan 2013 14:00:29 GMT

An excellent post, as always. I just wished you'd written it months ago. The issue with passing async lambdas around bit me more than once before I realized what I was doing wrong! And it's not always obvious immediately.

re: Psychic Debugging of Async Methods

James Chaldecott — Tue, 29 Jan 2013 09:53:10 GMT

Somewhat related to this

Is there any way to see in a debugger a list of outstanding awaits?

If not, would it even be possible to write an add-in or debugger visualizer or something (at least for the common case of looking for outstanding Task continuations)?

It's a bit weird in a program with lots of async operations pending that you can hit "pause" in the debugger and have no idea what state the program is actually in. It's particularly irksome when the async operations are each themselves made up of multiple async operations.

re: Psychic Debugging of Async Methods

Damien — Tue, 29 Jan 2013 06:49:59 GMT

There's a second bug in 3) b) - Reset is locking on a different object than the other methods. So the locking is all broken anyway. (I know it's not the main theme of this post - but it's a common problem with locking issues)