It is something we take for granted every time we run a .NET program, but it turns out that loading a Type or class is a fairly complex process. So how does the .NET Runtime (CLR) actually load a Type? If you want the tl;dr it’s done carefully, cautiously and step-by-step Ensuring Type Safety One of...

Turns out that what I’d always thought of as “Compiler magic” or “Syntactic sugar” is actually known by the technical term ‘Lowering’ and the C# compiler (a.k.a Roslyn) uses it extensively. But what is it? Well this quote from So You Want To Write Your Own Language? gives us some idea: Lowering One ...

Now that the CoreCLR is open-source we can do fun things, for instance find out if it’s possible to add new IL (Intermediate Language) instruction to the runtime. TL;DR it turns out that it’s easier than you might think!! Here are the steps you need to go through: Step 0 - Introduction and Backgroun...

A while ago I wrote about the ‘special relationship’ that exists between Strings and the CLR, well it turns out that Arrays and the CLR have an even deeper one, the type of closeness where you hold hands on your first meeting As an aside, if you like reading about CLR internals you may find these ot...

If you’re near London at the end of April, I’ll be speaking at ProgSCon 2017 on Microsoft and Open-Source – A ‘Brave New World’. ProgSCon is 1-day conference, with talks covering an eclectic range of topics, you’ll learn lots!! As part of a never-ending quest to explore the CoreCLR source code I stu...

Whilst writing a previous blog post I stumbled across the .NET Interpreter, tucked away in the source code. Although, it I’d made even the smallest amount of effort to look for it, I’d have easily found it via the GitHub ‘magic’ file search: Usage Scenarios Before we look at how to use it and what i...

photo by Alan O’Rourke Just over 2 years ago Microsoft open-sourced the entire .NET framework, this posts attempts to provide a ‘Hitchhikers Guide’ to the source-code found in the CoreCLR GitHub repository. To make it easier for you to get to the information you’re interested in, this post is split ...

Because the CLR is a managed environment there are several components within the runtime that need to be initialised before any of your code can be executed. This post will take a look at the EE (Execution Engine) start-up routine and examine the initialisation process in detail. (*) 68 is only a ro...

Delegates are a fundamental part of the .NET runtime and whilst you rarely create them directly, they are there under-the-hood every time you use a lambda in LINQ (=>) or a Func<T>/Action<T> to make your code more functional. But how do they actually work and what’s going in the CLR when you use the...

Over the last few months there have been several blog posts looking at GC pauses in different programming languages or runtimes. It all started with a post looking at the latency of the Haskell GC, next came a follow-up that compared Haskell, OCaml and Racket, followed by Go GC in Theory and Practic...

According to the NASA ‘Near Earth Object Program’ asteroid ‘101955 Bennu (1999 RQ36)’ has a Cumulative Impact Probability of 3.7e-04, i.e. there is a 1 in 2,700 (0.0370%) chance of Earth impact, but more reassuringly there is a 99.9630% chance the asteroid will miss the Earth completely! But how doe...

It’s common knowledge that reflection in .NET is slow, but why is that the case? This post aims to figure that out by looking at what reflection does under-the-hood. CLR Type System Design Goals But first it’s worth pointing out that part of the reason reflection isn’t fast is that it was never desi...

This post is completely inspired by (or ‘copied from’ depending on your point of view) a recent post titled JAVA PAPERS (also see the HackerNews discussion). However, instead of looking at Java and the JVM, I’ll be looking at references to research papers in the .NET language, runtime and compiler s...

A little over 2 years ago Microsoft announced that they were open sourcing large parts of the .NET framework and as Scott Hanselman said in his recent Connect keynote, the community has been contributing in a significant way: You can see some more detail on this number in the talk ‘What’s New in the...

Well it turns out that it’s a really nice example of collaboration between the main parts of the .NET runtime, here’s a list of all the components involved: Compiler JITter CLR Garbage Collector (GC) Now you could argue that all of these are required to execute any C# code, but what’s interesting ab...

The dotnet CLI tooling comes with several built-in cmds such as build, run and test, but it turns out it’s possible to add your own verb to that list. Arbitrary cmds From Intro to .NET Core CLI - Design The way the dotnet driver finds the command it is instructed to run using dotnet {command} is via...

What’s the problem with LINQ? As outlined by Joe Duffy, LINQ introduces inefficiencies in the form of hidden allocations, from The ‘premature optimization is evil’ myth: To take an example of a technology that I am quite supportive of, but that makes writing inefficient code very easy, let’s look at...

In the CLR strings are stored as a sequence of UTF-16 code units, i.e. an array of char items. So if we have the string ‘testing’, in memory it looks like this: But look at all those zero’s, wouldn’t it be more efficient if it could be stored like this instead? Now this is a contrived example, clear...

In which we use System.Runtime.CompilerServices.Unsafe a generic API (“type-safe” but still “unsafe”) and mess with the C# Type System! The post covers the following topics: What it is and why it’s useful How it works Code samples Tricks you can do with it Using it safely What it is and why it’s use...

If you’ve ever spent time debugging .NET memory dumps in WinDBG you will be familiar with the commands shown below, which aren’t always the most straight-forward to work with! However back in May 2013 Microsoft released the CLR MD library, describing it as: … a set of advanced APIs for programmatica...

Recently Roger Johansson wrote a post titled Wire – Writing one of the fastest .NET serializers, describing the optimisation that were implemented to make Wire as fast as possible. He also followed up that post with a set of benchmarks, showing how Wire compared to other .NET serialisers: Using Benc...

Pauses are a known problem in runtimes that have a Garbage Collector (GC), such as Java or .NET. GC Pauses can last several milliseconds, during which your application is blocked or suspended. One way you can alleviate the pauses is to modify your code so that it doesn’t allocate, i.e. so the GC has...

GC pauses are a popular topic, if you do a google search, you’ll see lots of articles explaining how to measure and more importantly how to reduce them. This issue is that in most runtimes that have a GC, allocating objects is a quick operation, but at some point in time the GC will need to clean up...

Just over a week ago the official 1.0 release of .NET Core was announced, the release includes: the .NET Core runtime, libraries and tools and the ASP.NET Core libraries. However alongside a completely new, revamped, xplat version of the .NET runtime, the development experience has been changed, wit...

As part of an ongoing attempt to learn more about how a real-life Garbage Collector (GC) works (see part 1) and after being inspired by Julia Evans’ excellent post gzip + poetry = awesome I spent a some time writing a tool to enable a live visualisation of the .NET GC in action. The output from the ...

Strings and the Common Language Runtime (CLR) have a special relationship, but it’s a bit different (and way less political) than the UK <-> US special relationship that is often talked about. This relationship means that Strings can do things that aren’t possible in the C# code that you and I can w...

Recently Nick Craver one of the developers at Stack Overflow has been tweeting snippets of code from their source, the other week the following code was posted: A daily screenshot from the Stack Overflow codebase (checking strings for tokens without allocations). #StackCode pic.twitter.com/sDPqviHgD...

A while ago I came across an interesting and very readable paper titled “COZ Finding Code that Counts with Causal Profiling” that was presented at SOSP 2015 (and was recipient of a Best Paper Award). This post is my attempt to provide an introduction to Causal Profiling for anyone who doesn’t want t...

In a previous post I looked at how you can use BenchmarkDotNet to help diagnose why one benchmark is running slower than another. The post outlined how ETW Events are used to give you an accurate measurement of the # of Bytes allocated and the # of GC Collections per benchmark. Inlining In addition ...

For a while now I’ve been involved in the Open Source BenchmarkDotNet library along with Andrey Akinshin the project owner. Our goal has been to produce a .NET Benchmarking library that is: Accurate Easy-to-use Helpful First and foremost we do everything we can to ensure that BenchmarkDotNet gives y...