Best practices to turn a .NET class library into a multithreaded .NET class library

Question

I have some C# class libraries, that were designed without taking into account things like concurrency, multiple threads, locks, etc...

The code is very well structured, it is easily expandable, but it can benefit a lot from multithreading: it's set of scientific/engineering libraries that need to perform billions of calculations in very-very short time (and now they don't take benefit from the available cores).

I want to transform all this code into a set of multithreaded libraries, but I don't know where to start and I don't have any previous experience.

I could use any available help, and any recommendations/suggestions.

Answer 1

My recommendation would be to not do it. You didn't write that code to be used in parallel, so it's not going to work, and it's going to fail in ways that will be difficult to debug.

Instead, I recommend you decide ahead of time which part of that code can benefit the most from parallelism, and then rewrite that code, from scratch, to be parallel. You can take advantage of having the unmodified code in front of you, and can also take advantage of existing automated tests.

It's possible that using the .NET 4.0 Task Parallel Library will make the job easier, but it's not going to completely bridge the gap between code that was not designed to be parallel and code that is.

Answer 2

I'd highly recommend looking into .NET 4 and the Task Parallel Library (also available in .NET 3.5sp1 via the Rx Framework).

It makes many concurrency issues much simple, in particular, data parallelism becomes dramatically simpler. Since you're dealing with large datasets in most scientific/engineering libraries, data parallelism is often the way to go...

For some reference material, especially on data parallelism and background about decomposing and approaching the problem, you might want to read my blog series on Parallelism in .NET 4 .

Answer 3

If you don't have any previous experience in multithreading then I would recommend that you get the basics first by looking at the various resources: https://stackoverflow.com/questions/540242/book-or-resource-on-c-concurrency

Making your entire library multithreaded requires a brand new architectural approach. If you simply go around and start putting locks everywhere in your code you'll end up making your code very cumbersome and you might not even achieve any performance increases.

The best concurrent software is lock-free and wait-free... this is difficult to achieve in C# (.NET) since most of your Collections are not lock-free, wait-free or even thread-safe. There are various discussions on lock-free data structures . A lot of people have referenced Boyet's articles (which are REALLY good) and some people have been throwing around The Task Parallel Library as the next thing in .NET concurrency, but TPL really doesn't give you much in terms of thread-safe collections.

.NET 4.0 is coming out with Collections.Concurrent which should help a lot.

Making your entire library concurrent would not be recommended since it wasn't designed with concurrency in mind from the start. Your next option is to go through your library and identify which portions of it are actually good candidates for multithreading, then you can pick the best concurrency solution for them and implement it. The main thing to remember is that when you write multithreaded code, the concurrency should result in increased throughput of your program. If increased throughput is not achieved (ie you either match or the throughput is less than in the sequential version), then you should simply not use concurrency in that code.

Answer 4

The best place to start is probably http://msdn.microsoft.com/en-us/concurrency/default.aspx

Good luck!