Eduasync

A while I ago I blogged about what had changed under the hood of async between the CTP and the VS11 Preview. Well, now that the VS11 Beta is out, it’s time to do it all again… Note that the code in this post is in the Eduasync codebase, under a different solution (Eduasync VS11.sln). Many of the old existing projects won’t compile with VS11 beta, but I’d rather leave them as they are for posterity, showing the evolution of the feature. Stephen Toub has an excellent blog post covering some of this, so while I’ll mention things he’s covered, … Continue reading Eduasync 20: Changes between the VS11 Preview and the Visual Studio 11 Beta

Today’s post involves the MagicOrdering project in source control (project 28). When I wrote part 16 of Eduasync, showing composition in the form of majority voting, one reader mailed me a really interesting suggestion. We don’t really need to wait for any of the tasks to complete on each iteration of the loop – we only need to wait for the next task to complete. Now that sounds impossible – sure, it’s great if we know the completion order of the tasks, but half the point of asynchrony is that many things can be happening at once, and we don’t … Continue reading Eduasync part 19: ordering by completion, ahead of time…

In preparation for CodeMash, I’ve been writing some more async code and decompiling it with Reflector. This time I’m using the Visual Studio 11 Developer Preview – the version which installs alongside Visual Studio 2010 under Windows 7. (Don’t ask me about any other features of Visual Studio 11 – I haven’t explored it thoroughly; I’ve really only used it for the C# 5 bits.) There have been quite a few changes since the CTP – they’re not visible changes in terms of code that you’d normally write, but the state machine generated by the C# compiler is reasonably different. … Continue reading Eduasync part 18: Changes between the Async CTP and the Visual Studio 11 Preview

In the last post I showed a method to implement "majority voting" for tasks, allowing a result to become available as soon as possible. At the end, I mentioned that I was reasonably confident that it worked because of the unit tests… but I didn’t show the tests themselves. I felt they deserved their own post, as there’s a bigger point here: it’s possible to unit test async code. At least sometimes. Testing code involving asynchrony is generally a pain. Introducing the exact order of events that you want is awkward, as is managing the threading within tests. With a … Continue reading Eduasync part 17: unit testing

(This post covers project 19 in the source code.) Last time we looked at independent coroutines running in a round-robin fashion. This time we’ll keep the round-robin scheduling, but add in the idea of passing data from one coroutine to another. Each coroutine will act on data of the same type, which is necessary for the scheme to work when one coroutine could "drop out" of the chain by returning. Designing the data flow It took me a while to get to the stage where I was happy with the design of how data flowed around these coroutines. I knew … Continue reading Eduasync part 14: Data passing in coroutines

(This post covers projects 16 and 17 in the source code.) Last time we looked at unwrapping an AggregateException when we await a result. While there are potentially other interesting things we could look at with respect to exceptions (particularly around cancellation) I’m just going to touch on one extra twist that the async CTP implements before I move on to some weird ways of using async. TPL and unobserved exceptions The Task Parallel Library (TPL) on which the async support is based has some interesting behaviour around exceptions. Just as it’s entirely possible for more than one thing to … Continue reading Eduasync part 12: Observing all exceptions

(This post covers projects 13-15 in the source code.) Long-time readers of this blog may not learn much from this post – it’s mostly going over what I’ve covered before. Still, it’s new to Eduasync. Why isn’t my exception being caught properly? Exceptions are inherently problematic in C# 5. There are two conflicting aspects: The point of the async feature in C# 5 is that you can write code which mostly looks like its synchronous code. We expect to be able to catch specific exception types as normal. Asynchronous code may potentially have multiple exceptions "at the same time". The … Continue reading Eduasync part 11: More sophisticated (but lossy) exception handling