Tag Archives: .NET

.NET DLLs Loaded Twice

If, like me, you’re still squeezing yourself into 32-bit Windows processes, you’re probably, also like me, constantly keeping an eye on the virtual address space usage of your application. If you happen to have used something like vmmap to take a peek at your memory contents, maybe you’ve noticed something strange with some .NET assemblies: they’re loaded twice! What’s going on…?
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C++: The oldest new kid on the block

TastyNobody could have failed to notice the recent resurgence of interest in the C++ programming language. In particular, the recent Build conference was the most we’ve seen Microsoft talking about C++ for several years. Why has a language that’s been languishing in the “prehistoric irrelevance” category for so long suddenly come back into vogue?
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Kinect SDK with F#

Just what do you think you're doing, Dave?
Just what do you think you're doing, Dave?
I finally got around to taking a look at the Kinect SDK the other day, partly because I was interested to see how the API looked from F#. Unfortunately getting it going turned out to be more of a pain than I was expecting.

The first bit was easy: I’m “lucky” enough to have one of the older Xboxes, which meant I’d had to get a Kinect with separate power, which is the one required by the SDK. Now all I needed was a Windows machine to develop on.
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F# Async: Plays well with others?

OK, quick Async pop quiz: How long does the run function below take to execute?

module Test = 
    let work i = 
        async { 
            return i+1 
    let run _ = 
        [1..1000] |> List.map work 
        |> Async.Parallel 
        |> Async.RunSynchronously

(Waits for people to start FSI and paste in the code…)

My guess would’ve been something just over 500ms; each of the 1000 async tasks would surely sleep in parallel, and then the operation itself is trivial. The additional elapsed time would be dominated by the overhead of thread management, and depend on the number of threads that can physically run in parallel (I’m using an 8-core machine). But still, something close to 500ms…

The actual result? 28000ms. Yes, you read that right: 28 seconds. What on earth did we do wrong?
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Mixing it up: when F# meets C#

If it were a perfect world, we’d all exist in a happy little bubble of our favourite programming language and you’d never have to worry about the nasty details of interacting with something written by – gasp – someone else in a – double-gasp – different language. But unfortunately that’s precisely what we have to do all the time. And that means that one day all of your fancy-pants algorithmic, highly parallel, functionally pure F# code is going to meet the world of “enterprise” C# development head-on.

Of course the idiomatic way to avoid problems at the boundary between your F# code and the outside world is to ensure that you only expose a small set of compatible types. This works pretty well if your clients are also .NET languages. For instance you can do things like exposing your collections as seq, rather than say, a native F# list, and this will mean your collections can be consumed as IEnumerable. The only problem is it means you’ve got the added burden of maintaining this mapping layer, because you’ll no doubt want to use the F# “native” types internally.

So, what options do we have if some of our F# types happen to leak into our public API? Luckily, lots. Let’s take a look at how some of the common F# constructs can be called from C#.
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Quick post: Using Mono.Cecil and F# to get assembly dependencies

One of the tools I use a lot when doing C++ development and debugging is “dependency walker”; an app that displays all the static dependencies of an executable. These are dependencies created by referencing functions from an import library (.lib file) at compile time. If any of the imported DLLs are missing at run-time, the executable will fail to load, normally with error 2: file not found. Obviously pretty disastrous in production. The .NET equivalent is the binding failure. You can track down what went wrong at runtime using fuslogvw, but I’ve often wished for a tool like ‘depends’ to work out up-front what dependencies are required. Luckily because assemblies includes a list of dependent libraries in the form of a manifest this information can be accessed using reflection.

Mono-gorilla-aqua.100pxI’m a big fan of the Mono.Cecil library for doing reflection (and more!) with .NET. I’ve had issues in the past where the built-in .NET reflection (using Assembly.ReflectionOnlyLoad) attempts to load dependent libraries as you iterate over exposed types, even though it’s not supposed to (unfortunately I don’t have a repro to hand). This makes it very difficult to work on an assembly without having all of its dependencies available. Cecil doesn’t have this problem because it accesses the assembly in a lower-level way.
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Minilight renderer in F#

Cornell Box in the evening
Cornell Box in the evening
I’m a sucker for eye-candy, and the other day I came across the beautifully lit renders produced by Minilight. It’s a nice, minimal implementation of a global illumination renderer that’s been ported to a wide variety of different languages from C to ActionScript. So of course, I couldn’t resist trying to implement it in F#.
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.NET 4.0 Type Equivalence causes BadImageFormatException

I recently discovered a nasty backward compatibility problem with the new type equivalence feature in .NET 4.0. Luckily it’s relatively difficult to hit it if you’re in a pure-C# environment, but if you happen to generate any assemblies directly using IL, you should watch out. Read on for all the gory details.
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