A while ago I was attending one of the Developer, Developer, Developer conference in Reading, and I heard Alex Davies give a talk about actors and async. He mentioned that he was in the process of writing a short book for O’Reilly about async in C# 5, and I offered to review it for him. Many months later (sorry Alex!) I’m finally getting round to it.
Disclaimer: The review copy was given to me for free, and equally the book is arguably a competitor of the upcoming 3rd edition of C# in Depth from the view of readers who already own the 2nd edition… so you could say I’m biased in both directions. Hopefully they cancel out.
This is a book purely on async. It’s not a general C# book, and it doesn’t even cover the tiny non-async features in C# 5. It’s all about asynchrony. As you’d expect, it’s therefore pretty short (92 pages) and can comfortably be consumed in a single session. Alex’s writing style is informal and easy to read. Of course the topic of the book is anything but simple, so even though you may read the whole book in one go first time, that doesn’t mean you’re likely to fully internalize it straight away. The book is divided into 15 short chapters, so you can revisit specific areas as and when you need to.
I’ve been writing and speaking about async for about two and a half years now. I’ve tried various ways of explaining it, and I’m pretty sure it’s one of those awkward concepts which really just needs to click eventually. I’ve had some mails from people for whom my explanation was the one to do the trick… and other mails from folks who only "got it" after seeing another perspective. I’d encourage anyone learning about async to read a variety of books, articles, blog posts and so on. I don’t even think it’s a matter of finding the single "right" explanation for you – it’s a matter of letting them all percolate.
The book covers all the topics you’d expect it to:
- Why asynchrony is important
- Drawbacks of library-only approaches
- How async/await behaves in general
- Threading and synchronization contexts
- Different code contexts (ASP.NET, WinRT, regular UI apps)
- How async code is compiled
Additionally there are brief sections on unit testing, parallelism and actors. Personally I’d have preferred the actors part to be omitted, with more discussion on the testing side – particularly in terms of how to write deterministic asynchronous tests. However, I know that Alex is a big fan of actors, so I can forgive a little self-indulgence on that front.
There’s one area where I’m not sure I agree with the advice in the book: exceptions. Alex repeatedly gives the advice that you shouldn’t let exceptions go unobserved. I used to go along with that almost without thinking – but now I’m not so sure. There are definitely cases where that definitely is the case, but I’m not as comfortable with the global advice as I used to be. I’ll try to put my thoughts in order on this front and blog about this separately at a later date.
That aside, this is a good, pragmatic book. To be honest, I suspect no book on async is going to go into quite as many details as the PFX team blog, and that’s probably a good thing. But "Async in C# 5.0" is a very good starting point for anyone wanting to get to grips with async, and I in no way begrudge any potential C# in Depth 3rd edition sales I may lose by saying so 😉